CL – Climate: Past, Present & Future

CL0 – Open Session on Climate: Past, Present and Future

EGU22-1953 | Presentations | CL0

Probabilistic Estimation of mid-Holocene global mean sea level 

Roger Creel, Jacqueline Austermann, Robert Kopp, Nicole Khan, Erica Ashe, Jonathan Kingslake, and Torsten Albrecht

Rising sea levels in the 21st century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.

Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.

 

How to cite: Creel, R., Austermann, J., Kopp, R., Khan, N., Ashe, E., Kingslake, J., and Albrecht, T.: Probabilistic Estimation of mid-Holocene global mean sea level , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1953, https://doi.org/10.5194/egusphere-egu22-1953, 2022.

EGU22-12297 | Presentations | CL0

Late Holocene sea-level change and storms in southwestern Norway based on new data from intertidal basins and salt marshes

Max Holthuis, Francis Chantel Nixon, Malin Kylander, Willem van der Bilt, Jake Martin, and Thomas Lakeman

Most relative sea level (RSL) curves in Norway have been solidly constructed using sea-level index points (SLIPs) from isolation basins. Many of these curves show RSL falling at a slow and steady rate to modern sea level during the late Holocene, despite a lack of SLIPs younger than ca. 2000 years. Tide gauge records from southern and western Norway indicate that RSL may have been rising since they were installed (ca. 100 years ago), while the few RSL curves with one or two SLIPs younger than 2000 years BP hint that rates of sea-level fall accelerated during this period. This study aims to close the gap between palaeo and instrumental data by generating late Holocene SLIPs from low-elevation and intertidal basins in southwestern Norway. Geochemical analyses of the sediment cores from all the studied areas thus far suggests that marine influence has been increasing in recent centuries, possibly due to rates of eustatic sea level rise overtaking residual glacioisostatic adjustment (ca. 1-2 mm/yr) from the Last Glacial Maximum. Anecdotal evidence from local residents of Egersund, with family histories and records of past storm levels going back to the 1800s, confirm this. Discrete storm layers consisting of shell fragments in one salt marsh at the back of a sheltered intertidal basin, however, may be overprinting any subtle trends in recent RSL rise. Full results of multi-proxy analyses of 8 cores from four salt marshes and protected, intertidal basins with bedrock sills will be presented from the southwestern corner of Norway.

How to cite: Holthuis, M., Nixon, F. C., Kylander, M., van der Bilt, W., Martin, J., and Lakeman, T.: Late Holocene sea-level change and storms in southwestern Norway based on new data from intertidal basins and salt marshes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12297, https://doi.org/10.5194/egusphere-egu22-12297, 2022.

EGU22-5004 | Presentations | CL0

Submerged beachrock: A tool for reconstructing relative sea level change example from Tekirdag coastline, Sea of Marmara, Turkey

Ufuk Tarı, Gürsel Sunal, Orkan Özcan, and Cenk Yaltırak

The beachrock formations represent a significant paleo-environmental proxy because they can record both the vertical and the horizontal evolution of the coastline. They have been used to assess Holocene coastline evolution and crustally induced relative sea level (RSL) change, notably in the Sea of Marmara. In this study, we report existence of the less known submerged beachrocks in the nearshore coastal area of Tekirdag city (Altinova), the northern Sea of Marmara. The beachrocks found in the Tekirdag coastline are locally spread, parallel to the coastline with an extend of about 5 km and at depths ranging from -2 to 0m below present sea level. The beachrock is defined by a calcite-cemented shoreline sandstone. The cement mineralogy and morphology of the beachrocks are indicative of the diagenetic environment, and therefore the examination of the cement characteristics and microstratigraphy can allow identify the type of cement and spatial relationship between the past shoreline and beachrock formation zone.

The Tekirdag coastal area is located in the western Marmara Region. The western coasts of the Marmara Region include a number of natural features inherited from their coastal evolution. Besides, relative sea level change during late Quaternary in this region and its vicinity are generally not homogeneous as a result of the tectonic activity controlled by the North Anatolian Fault Zone (NAFZ) which played a crucial role in the coastline evolution at different periods of the region.

The aim of our study to reconstruct the shoreline modification using beachrocks in the study area. For this purpose, we coupled a series of methodologies for the paleo-environmental and geomorphological study of the coastal zone and the shallow submarine area, which included: a) coring from submerged beachrocks, b) petrographic and microstratigraphic analyses of cementation, c) monitoring of underwater beachrocks and coastal zone by drone and e) dating the formation of beachrocks. Through our analyses we aim to better contribute the use of beachrocks as accurate proxies for the RSL variation in the study area.

 

How to cite: Tarı, U., Sunal, G., Özcan, O., and Yaltırak, C.: Submerged beachrock: A tool for reconstructing relative sea level change example from Tekirdag coastline, Sea of Marmara, Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5004, https://doi.org/10.5194/egusphere-egu22-5004, 2022.

EGU22-12629 | Presentations | CL0 | Highlight

Extending paleo-tsunami records south of the 2004 Indian Ocean Tsunami patch, Sumatra, Indonesia: 2022 update

Jedrzej Majewski, Geoffrey Richards, Patrick Daly, Adam Switzer, Nazli Ismail, Tomi Afrizal, Margaret Christie, and Benjamin Horton

Our team has previously built a ~7500 year tsunami history for the northern patch of the Sunda Megathrust. However, the paleo-tsunami history south of Aceh province and the 2004 rupture patch remains poorly understood. We conducted geological investigation to better define the boundaries of rupture patches along the Megathrust.

 

We utilized satellite imagery to pinpoint potential sites likely to archive evidence of paleo tsunami inundations and co-seismic land-level change. Due to the continuing Covid-19 pandemic and restrictions, our researchers from Singapore, and USA could not travel to Indonesia. However, because of the longstanding close collaboration between the Earth Observatory of Singapore and Syiah Kuala University, Banda Aceh, Indonesia, the project continued to progress. The Syiah Kuala University team investigated nearly 20 sites between Banda Aceh in the northern patch of the of Sumatra Megathrust and Padang in the south. Several sites preserved probable paleo-tsunami sediments. The paleo-tsunami sediments were identified from anomalous layers of sand in low energy environments where they would not normally occur, such as mangroves, coastal lowlands, and/or swales.

 
Here we present results of litho-, bio- and chronostratigraphical analysis from Susoh as well as preliminary information from sites along the coastline between Meulaboh and Padang. From Susoh we described stratigraphy from a series of cores to a depth of 4.75 m. The top 2.5 meters was dominated by muds typical of estuarine or tidal flat settings, but it is interrupted by three pulses of sandy muds. At 2.55 m we encountered a 0.2 m thick layer of course sand, underlain by a 0.5 m thick mangrove peat with a gradual transition into organic sandy muds and sands. Pollen analysis from the fine-grained organic layers indicate they were formed in a mangrove environment. Radiocarbon dating of the organic macrofossils from the mangrove peat indicate the tsunami event occurred post 1850 cal. yrs BP. Our research continues to improve our understanding of the Sumatran Megathrust.

How to cite: Majewski, J., Richards, G., Daly, P., Switzer, A., Ismail, N., Afrizal, T., Christie, M., and Horton, B.: Extending paleo-tsunami records south of the 2004 Indian Ocean Tsunami patch, Sumatra, Indonesia: 2022 update, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12629, https://doi.org/10.5194/egusphere-egu22-12629, 2022.

EGU22-5675 | Presentations | CL0

Late Holocene sea-level change in southern New Zealand 

Ed Garrett, Roland Gehrels, Bruce Hayward, Rewi Newnham, Maria Gehrels, Craig Morey, and Sonke Dangendorf

We present new proxy-based sea-level reconstructions for southern New Zealand spanning the last millennium. These palaeo sea-level records usefully complement sparse Southern Hemisphere proxy and tide-gauge sea-level datasets and, in combination with instrumental observations, can test hypotheses about the drivers of 20th century global sea-level change, including land-based ice melt and regional sterodynamics. We develop sea-level transfer functions from regional datasets of salt-marsh foraminifera to establish a new proxy-based sea-level record at Mokomoko Inlet, at the southern tip of the South Island, and to improve the previously published sea-level reconstruction at Pounawea, located about 110 km to the east. Chronologies are based on radiocarbon, radiocaesium, stable lead isotope and pollen analyses. Both records are in good agreement and show sea level several decimetres below present over the last millennium, before a rapid sea-level rise in the first half of the 20th century that reached maximum rates in the 1940s. Previously reported discrepancies between proxy-based sea-level records and tide-gauge records are partially reconciled by accounting for barystatic and sterodynamic components of regional sea-level rise. We conclude that the rapid sea-level rise during the middle 20th century along the coast of southern New Zealand was primarily driven by regional thermal expansion and ocean dynamics.

How to cite: Garrett, E., Gehrels, R., Hayward, B., Newnham, R., Gehrels, M., Morey, C., and Dangendorf, S.: Late Holocene sea-level change in southern New Zealand , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5675, https://doi.org/10.5194/egusphere-egu22-5675, 2022.

EGU22-4085 | Presentations | CL0

Influence of climate change on water balance of the lowlands of southeastern Peru

Santos J. González-Rojí, Martina Messmer, Christoph C. Raible, and Thomas F. Stocker

EGU22-7988 | Presentations | CL0

Ancient Tillandsia landbeckii dune ecosystems and their potential to reveal past variations in coastal fog moisture during the Holocene in the Atacama Desert

Claudio Latorre, Sergio Contreras, Andrea Jaeschke, Juan Luis Garcia, and Camilo del Río

Tillandsia landbeckii is a bromeliad that inhabits the hyperarid coast of the Atacama Desert where it survives solely on moisture and nutrients from fog. It does so by constituting a unique dune ecosystem that maximizes its fog capture potential as well as preserving layers of buried tillandsia plants. These buried layers can survive over multiple millennia and here we present data based on stratigraphic, radiocarbon, stable isotopes, and leaf wax analyses that we are applying to these ancient leaves and stems to reconstruct past variations in fog moisture and nutrient cycling. Some of the oldest buried layers date back to >10,000 14C yrs BP and our results show that both d15N and leaf waxes are capable of tracking variations in moisture changes although we observed significant variation in d15N values across living plants which may be due to the plants' age. Past variations in fog likely track variations in large-scale synoptic climate features such as the height of the Marine Boundary Layer and the strength of the Southern Pacific Anticyclone.

How to cite: Latorre, C., Contreras, S., Jaeschke, A., Garcia, J. L., and del Río, C.: Ancient Tillandsia landbeckii dune ecosystems and their potential to reveal past variations in coastal fog moisture during the Holocene in the Atacama Desert, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7988, https://doi.org/10.5194/egusphere-egu22-7988, 2022.

EGU22-10055 | Presentations | CL0

Fjord sedimentary signature of the last surging phase of Pio XI Glacier (Chilean Patagonia)

Loic Piret, Sebastien Bertrand, and Carlos Moffat

Proglacial sediments hold continuous and high-resolution records of past glacier dynamics. In this study, we examine the sediments of Eyre Fjord (Chilean Patagonia, 49°S), which is fed by Pio XI Glacier, to gain a better understanding of how the surging phase of a growing glacier is recorded in marine sediments. Pio XI Glacier has experienced a net advance of >10 km since 1945 and has had several surging phases that each last 2 – 3 years and occur every ~14 years. The last reported surging phases happened between 1976 – 1979, 1997 – 1998, and 2014 – 2018. Thirty CTD profiles taken in the fjord along one longitudinal and three transverse transects in February 2019 show that sediment transfer through the fjord during a quiescent (i.e., non-surging) phase in summer primarily happens by means of widespread (unchannelised) hyperpycnal flows that are 20 – 100 m thick. To assess spatiotemporal variability in sedimentation throughout the fjord, nine sediment cores were collected in 2019. Concentrations of short-lived radionuclides suggest a sedimentation rate of 3 – 20 cm/year. Sediment grain size and magnetic susceptibility, (CT) density, and inorganic geochemistry (Fe, Ti, K, Mn, Zr, Zn, Rb, Sr), which were obtained at higher resolution, were used as proxies for hydrodynamic conditions in the fjord. The longest sediment record holds fine glacial mud and low density sediments between 135 – 70 cm and in the upper 10 cm, which indicate relatively low hydrodynamic activity, likely corresponding to the quiescent phases before 2014 after 2018. Between 70 cm and 10 cm, the overall denser and coarser sediments intercalated with cm-thick sandy layers indicate higher hydrodynamic activity and flood events, most likely representing the most recent (2014 – 2018) surging phase of the glacier. Interestingly, the thickest and coarsest flood deposits seem to be concentrated at the top of the sediment unit that represents the surging phase suggesting that the floods are the most intense towards the end of the surging phase. Overall, these results show that quiescent and surging phases of surge-type glaciers leave distinct sedimentary signatures in fjord sediments, offering the possibility to use longer sediment records to identify former surging phases.

How to cite: Piret, L., Bertrand, S., and Moffat, C.: Fjord sedimentary signature of the last surging phase of Pio XI Glacier (Chilean Patagonia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10055, https://doi.org/10.5194/egusphere-egu22-10055, 2022.

EGU22-133 | Presentations | CL0

Process-based GCMs evaluation over South Tropical South America during the dry-to-wet transition season following a weather typing approach

Matias Olmo, Jhan Carlo Espinoza, Maria Laura Bettolli, Juan Pablo Sierra, Clementine Junquas, and Paola Arias

The representation of the South American Monsoon System (SAMS) by global climate models (GCMs) is of key relevance for a better comprehension of the physical mechanisms behind the recent and future climate changes over South Tropical South America (STSA) in a global warming scenario. During the last four decades STSA experimented a lengthening of the dry season related to diverse forcings, leading to an increase in fire activity and severe socio-environmental impacts. In the present study, a set of 16 GCMs simulations from the CMIP6 experiment were evaluated during the historical period 1979-2014 in terms of how well they reproduced the atmospheric circulation over STSA through a weather-typing (WTs) approach. 9 WTs were first identified based on low-level wind anomalies from the ERA5 reanalysis, which summarized the atmospheric variations over STSA throughout the year. Focus was put on the representation of WTs during the SAMS initiation and the dry-to-wet transition season (from July to October). Model performance depended on the seasonal cycle and spatial structure of the WTs. Some of the GCMs adequately reproduced the different WTs and their spatio-temporal configurations, with lower skills in the transition seasons. Furthermore, GCMs tended to go from dry to wet conditions too quickly, evidencing deficiencies in the representation of the SAMS onset. This was particularly associated with a poor representation of the southerly wind intrusions to STSA and the intra-seasonal variability of the South American low-level jet. In terms of the relationship between WTs and rainfall on interannual time-scales, a selection of GCMs was able to associate the occurrence of anomalous wet and dry years with specific WTs, indicating well-represented physical processes modulating precipitation variability. Overall, this study could identify few GCMs that managed to simulate the main atmospheric circulation features in STSA (among them, the CESM2, CMCC-CM2-HR4 and MPI-ESM1-2-HR models), which is particularly important for driving high-resolution modelling experiments as well as for the analysis of future projections.

How to cite: Olmo, M., Espinoza, J. C., Bettolli, M. L., Sierra, J. P., Junquas, C., and Arias, P.: Process-based GCMs evaluation over South Tropical South America during the dry-to-wet transition season following a weather typing approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-133, https://doi.org/10.5194/egusphere-egu22-133, 2022.

EGU22-10721 | Presentations | CL0 | Highlight

Long term characterization of heat waves in Brazil and their impacts on mortality rates

Djacinto Monteiro dos Santos, Beatriz N. Garcia, João L. Geirinhas, Ana Russo, Leonardo F. Peres, and Renata Libonati

Climate Change has increased the intensity, duration, and frequency of extreme weather events such as heatwaves (HW), which have impacts on ecosystems, economics, and human populations, including adverse health effects and the increase in the number of deaths due to the heat stress. However, there are still few studies evaluating the occurrence of adverse health due to HW in South America. Particularly in Brazil, regional differences in the effects of heatwaves are expected due to their continental dimensions, which makes it necessary to carry out local studies. This work presents a long term analysis of the occurrence of HW in the 14 major metropolitan regions (MRs) in Brazil, namely: Manaus, Belém, Salvador, Recife, Fortaleza, Goiânia, Brasília, Cuiabá, São Paulo, Rio de Janeiro, Belo Horizonte, Porto Alegre, Curitiba and Florianópolis. Observational temperature data (1970-2020) provided by the National Institute of Meteorology (INMET) were used to compute the Extreme Heat Factor (EHF) index, which was used to identify and classify HW in terms of severity.  Significant and positive trends in the frequency of HW were observed over decades in all MRs, particularly in the north (Manaus and Belém) and central west region (Goiania and Brasilia). Particularly, from 2014 to 2019, all the MRs presented HW regime every year, including severe and/or extreme events. In general, the longest and the most intense HW in Brazilian MRs occurred in the last decade (2010-2020), with the exception of the 1997–1998 El Niño-related events. Daily mortality and hospital admission data from the Brazilian Public Health System (SUS) were used to assess the relationships between HW and health. Results indicate excess mortality (observed to expected ratio) during HW events in the MRs studied, with the elderly being the most vulnerable age group, in agreement with previous studies. The cause of death and the gender susceptibility to HW were also analyzed, and the results vary among the different MRs. This work provides an extensive characterization of the occurrence of HW in Brazil and valuable insights for the implementation of public mitigation and adaptation strategies in some of the most populated regions of South America.

This work was supported by FIOCRUZ [grant VPPCB-003-FIO-19] and FAPERJ [grant E26/202.714/2019]. D.M.S. was supported by FIOCRUZ [grant VPPCB-003-FIO-19].

How to cite: Monteiro dos Santos, D., N. Garcia, B., L. Geirinhas, J., Russo, A., F. Peres, L., and Libonati, R.: Long term characterization of heat waves in Brazil and their impacts on mortality rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10721, https://doi.org/10.5194/egusphere-egu22-10721, 2022.

EGU22-1340 | Presentations | CL0

Evaluation of lipid biomarkers as proxies for sea ice and ocean temperatures along the Antarctic continental margin

Juliane Müller, Nele Lamping, Jens Hefter, Gesine Mollenhauer, Haas Christian, Xiaoxu Shi, Maria-Elena Vorrath, Gerrit Lohmann, and Claus-Dieter Hillenbrand

EGU22-10609 | Presentations | CL0

Pre-satellite retreat of Thwaites and Pine Island glaciers: Recent results from sediment cores

Julia Wellner, Rachel Clark, Asmara Lehrmann, Allison Lepp, Claus-Dieter Hillenbrand, Rebecca Totten, Lauren Simkins, Michael Comas, Elaine Mawbey, Rebecca Hopkins, James Smith, John Anderson, Kelly Hogan, Frank Nitsche, Alastair Graham, and Robert Larter

Thwaites Glacier (TG) is thinning and accelerating while sitting on a landward-dipping bed, with an ice shelf that is rapidly disintegrating and losing its ability to buttress ice flow from upstream, and is in deep water that allows warm Circumpolar Deep Water (CDW) to reach its grounding zone.  Significant retreat of TG would trigger loss of ice across the region.  In recent decades, the mass balance of TG has become increasingly negative, suggesting that unstable retreat may have already begun.  The Thwaites Offshore Research (THOR) group has just completed four field deployments aimed at understanding the recent history of TG and neighboring ice, including Pine Island Glacier (PIG).  Three cruises on the RVIB N.B. Palmer, combined with sub-ice-shelf sediment coring, provide a suite of new data along the TG and PIG margins.  Data include multibeam surveys, 3.5 kHz subbottom profiler, over 100 new sediment cores, and high-resolution seismic profiles.  Break-up of floating ice cover in front of TG in 2019 allowed surveying of previously unmapped seafloor.  Major calving of PIG in 2020 allowed marine surveying over the locations where sub-ice-shelf cores were collected in the past, allowing direct ties between ice-based and marine work.  As of this writing in January 2022, we are entering into the Amundsen Sea for our third marine field season. 

 

Sediment cores record the history of grounding-zone retreat and ice interaction with the ocean over timescales from decades to several thousand years.  Proxies used to reconstruct ice and ocean histories include sedimentary facies analysis, diatom and foraminiferal assemblage data, and geochemical analyses.  Sedimentological analyses show a diverse array of lithofacies attributed to different environmental conditions.  Many cores across the region contain laminated mud with sparse gravel and sand, suggesting deposition of meltwater deposits. Downcore 210Pb measurements are used to create age models of the past ~100 years.  Combination of ages with facies models, including CT scans, reveals that the progressive detachment of Thwaites from pinning points began in the mid twentieth century, coincident with retreat of PIG (Smith et al., 2017) and with increasing advection of warm water onto the Amundsen shelf (Hillenbrand et al., 2017).  Conversely, Cranton Bay, to the northeast of PIG and separated from Pine Island Bay by a shallow sill, appears to be characterized by cold deep water and high productivity, allowing it to serve as an endmember different from the records obtained proximal to the large glacial outlets where CDW is impinging.

 

The satellite record of glacial retreat is inherently short.  Observations are accumulating about forcing mechanisms that can impact the stability of ice, such as increased CDW on the Amundsen Sea shelf.  However, without the time to observe the response of the ice, discovery of the forcing mechanisms is just half the story.  The other half of the story is completed by using the paleo record to see how ice has responded to drivers in the past.

How to cite: Wellner, J., Clark, R., Lehrmann, A., Lepp, A., Hillenbrand, C.-D., Totten, R., Simkins, L., Comas, M., Mawbey, E., Hopkins, R., Smith, J., Anderson, J., Hogan, K., Nitsche, F., Graham, A., and Larter, R.: Pre-satellite retreat of Thwaites and Pine Island glaciers: Recent results from sediment cores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10609, https://doi.org/10.5194/egusphere-egu22-10609, 2022.

EGU22-6484 | Presentations | CL0

Tracking ice-sheet dynamics by detrital feldspar Pb-isotope and 87Rb/87Sr dating during the Middle Miocene Climatic Transition, Weddell Sea, Antarctica

Roland Neofitu, Chris Mark, Suzanne O'Connell, Samuel Kelley, Delia Rösel, Thomas Zack, Michael Flowerdew, and J. Stephen Daly

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ18O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT is also an important tool for forecasting effects of anthropogenic climate change.

Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (K-feldspar only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), the combination with in-situ Sr-isotope fingerprinting and 87Rb/87Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, recovered from the Weddell Sea, ca. 750 km from the continental rise in 4671 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14.09 to 14.26 Ma.

Our findings are consistent with predictions made by recent palaeo-ice sheet models (eg., Gasson et al. 2016), which predict the development of sizeable and discrete embayments around the continent, including the Weddell Sea. We argue that the IRD derived from the unstable sector associated with this embayment formation at the time.

Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).

Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.

Gasson, E, et al., 2016, Proceedings of the National Academy of Sciences, v. 113, (13), p. 3459-3464, doi: www.pnas.org/cgi/doi/10.1073/pnas.1516130113.

Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

How to cite: Neofitu, R., Mark, C., O'Connell, S., Kelley, S., Rösel, D., Zack, T., Flowerdew, M., and Daly, J. S.: Tracking ice-sheet dynamics by detrital feldspar Pb-isotope and 87Rb/87Sr dating during the Middle Miocene Climatic Transition, Weddell Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6484, https://doi.org/10.5194/egusphere-egu22-6484, 2022.

EGU22-10174 | Presentations | CL0

Sedimentological facies characterization of Pliocene key interglacial-glacial intervals, IODP site 1361A, East Antarctic Wilkes Land margin

Julia Gutiérrez-Pastor, Carlota Escutia, Francisco José Jiménez-Espejo, Andrés Salvador Rigual-Hernández, María Ángeles Bárcena, Robert McKay, and Cecilia Morales

Marine sediment cores containing a unique Pliocene paleoenvironmental record were collected from the East Antarctic Wilkes Land continental rise by the IODP Expedition 318 at Site U1361 (Escutia et al., 2011). Site U1361 is located in front of the Wilkes Subglacial Basin (WSB) were, today, the East Antarctic Ice Sheet (EAIS) is grounded below sea level (marine-based) and therefore more vulnerable to climate changes.

We have conducted a facies analysis using shipboard measurements taken during Expedition 318 (i.e., physical properties data such as density (GRA) and magnetic susceptibility (MST) and high-resolution digital images), complemented with continuous elemental geochemical analyses. In addition, we have conducted high-resolution siliceous microfossil analyses to characterize past “warmer-than-present” intervals during the Pliocene warm period (~ 3-5 Ma) and their terminations recorded in site U1361 between ~ 73 to 123 mbsf. Our study is complemented by a pilot high-resolution detailed work on siliceous microfossils conducted from 3.69 to y 3.56 Ma that captures changes in sea ice cover and oceanic conditions (Armbrecht et al., 2018).

Preliminary analyses show that sediments consist of alternating intervals of interglacial diatom-rich/bearing silty clay with dispersed clasts that are ~ 0.5 to 8 m thick, and glacial sparsely laminated bioturbated clays with occasionally dispersed clasts.  In general, interglacial sediments is characterized by lower density, higher MST values, lower Mn/Ti and Fe/Ti ratios, and high Ca/Al, Si/Al, and Ba/Al ratios. Bioturbated clay with any dispersed clasts has a marked opposite trend (i.e., higher density, lower MST values, lower Ca/Al, Si/Al, and Ba/Al ratios and higher Mn/Ti and Fe/Ti ratios). This changes in lithology, physical properties and geochemical composition record significant changes in paleoenvironmental conditions. However, each glacial/interglacial (and vice versa) period exhibit specific characteristics and diatom associations pointing to different sea ice conditions during the selected Pliocene intervalsthat can be indirectly linked to ice-sheet dynamics in the Wilkes Subglacial Basin. The results of this study are relevant in order to understand the response of the EAIS dynamics and marine biota to an increase of the ocean surface temperatures during the transition from atmospheric CO2 concentrations similar to pre-industrial to concentrations close to present values (410 ppm).

This work has been conducted in the frame of projects H2020-MSCA-IF-2018-ANTICE-841980/CTM2017-89711-C2-1-P and is a contribution to the SCAR INSTANT Program.

Escutia, C. et al., 2011 doi:10.2204/​iodp.proc.318.105.2011

Armbrecht et al., 2018. doi:10.1016/j.marmicro.2017.10.008

How to cite: Gutiérrez-Pastor, J., Escutia, C., Jiménez-Espejo, F. J., Rigual-Hernández, A. S., Bárcena, M. Á., McKay, R., and Morales, C.: Sedimentological facies characterization of Pliocene key interglacial-glacial intervals, IODP site 1361A, East Antarctic Wilkes Land margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10174, https://doi.org/10.5194/egusphere-egu22-10174, 2022.

EGU22-10278 | Presentations | CL0

Ice shelf stability and glacial history in coastal Dronning Maud Land, East Antarctica

Hannes Eisermann, Graeme Eagles, Antonia Ruppel, and Wilfried Jokat

CL1.1.1 – Deep-time climate change: insights from models and proxies

EGU22-8237 | Presentations | CL1.1.1

The hydrological cycle in the past 540 million years

Yongyun Hu, Xiang Li, and Zhibo Li

Earth has undergone dramatic temperature fluctuations and the tectonic process of continental breaking up and reassembling in the past 540 million years. How these caused changes in the global hydrological cycle is an interesting question. To study the evolution of the global hydrological cycle since the Cambrian, we carried out 55 equilibrium simulations to simulate climate evolution in the past 540 million years, using CESM1.2.2. It is found that the global mean precipitation is closely correlated with the global mean surface temperature (GMST), especially oceanic precipitation has high correlation with GMST, with a coefficient of 0.92. Land precipitation also has statistically significant correlation with GMST. However, the correlation coefficient is much lower. Further analysis shows that land precipitation is also determined by continental fragmentation, mean latitudes, and total area, and that the semi-arid area is most sensitive to GMST changes.

How to cite: Hu, Y., Li, X., and Li, Z.: The hydrological cycle in the past 540 million years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8237, https://doi.org/10.5194/egusphere-egu22-8237, 2022.

EGU22-4335 | Presentations | CL1.1.1

Climate conditions of coals and evaporates in the Earth history

Xiujuan Bao and Yongyun Hu

Coals and evaporates are the most commonly used paleoclimate indicators, regarded as representatives of humid and arid climate conditions in the geological record, respectively. However, the quantitative and systematic climate significance of coals and evaporates in the Earth history still unknown. Here, we perform a series of simulations to simulate global climate conditions of Phanerozoic, using an Earth system model CESM 1.2.2 and reconstructed paleotopographies (Scotese, 2018). Combining with a global-scale complication of coals and evaporate from the present back to Devonian (Boucot et al., 2013), climate variables of annual average surface temperature (AAST), annual average precipitation (AAP) and annual average net precipitation (AANP) of the area where coals and evaporates formed are extracted for analysing quantitative climate conditions of coals and evaporates. The preliminary results show that (1) AAST of evaporate areas vary with global mean temperature, while the variation of coals areas’ AAST reflect a stage change,which are consistent with the stage evolution of land plant and lignin-degrading fungi; (2) AAP and AANP of coals and evaporates areas are relatively stable through the Earth history. Coals areas have general more AAP and AANP than evaporates in 25%-75% quantiles but have similar range with evaporites areas in 5%-95% quantiles.

 

Key words: coals, evaporates, plant evolution, deep-time climate, numerical simulation

References

Scotese C R, 2018. PALEOMAP PaleoAtlas Rasters[J].

Boucot A J, Chen X, Scotese C R, 2013. Lithology Data Tables[J].

How to cite: Bao, X. and Hu, Y.: Climate conditions of coals and evaporates in the Earth history, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4335, https://doi.org/10.5194/egusphere-egu22-4335, 2022.

EGU22-5167 | Presentations | CL1.1.1

Snowball Earth initiation and the thermodynamics of sea ice

Johannes Hörner, Aiko Voigt, and Christoph Braun

Snowball Earth is a hypothesized state in the deep past of Earth in which the ocean was completely or nearly completely covered by sea ice, resulting from a runaway ice-albedo feedback. Here, we address how the treatment of sea-ice thermodynamics affects the initiation of a Snowball Earth in the global climate model ICON-A run in an idealized slab-ocean aquaplanet setup. Specifically, we study the impact of vertical resolution and brine pockets of ice by comparing the 3-layer Winton and a 0-layer Semtner scheme, and we investigate the impact of limiting ice thickness to 5m.

The internal heat storage of ice is increased by higher vertical resolution and brine pockets, which weakens surface melting and increases global albedo by allowing snow and ice to persist longer into the summer season. The internal heat storage weakens the melt-ratchet effect, as is confirmed with offline simulations with the two ice schemes. The result is a substantially easier Snowball Earth initiation and an increase in the critical CO2 for Snowball initiation by 50%. Limiting ice thickness impedes Snowball initiation as the removal of excess ice leads to an artificial heat source. Yet, the impact is minor and critical is decreased by 5% only.

The results show that while the sea-ice thickness limit plays only a minor role, the internal heat storage of ice represents an important factor for Snowball initiation and needs to be taken into account when modeling Snowball Earth initiation.

How to cite: Hörner, J., Voigt, A., and Braun, C.: Snowball Earth initiation and the thermodynamics of sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5167, https://doi.org/10.5194/egusphere-egu22-5167, 2022.

EGU22-4906 | Presentations | CL1.1.1 | Highlight

Evolution of Dust and Its Climatic Impact during Earth’s History

Yonggang Liu, Qifan Lin, Ming Zhang, Peng Liu, Jian Zhang, and Zhengyu Liu

Dust, as one of the most common types of atmospheric aerosol, affects climate in many different ways. Atmospheric dust scatters and absorbs sunlight and reduces solar radiation received at the surface; it absorbs and emits longwave radiation, having a greenhouse effect; it has a complex indirect effect on climate by serving as cloud nuclei; when deposited on snow or ice, it reduces the surface albedo and warms the surface. Despite its importance in the climate system, how the dust emission and atmospheric dust loading varied during the Earth history is unclear. Here I will give a summary of the atmospheric dust loading as well as its climatic impact for a few typical periods of the Earth. All the results are from numerical simulations and are still premature due to uncertainties in vegetation cover and soil erodibility, and biases and inability of the climate model used.

In present day, the atmospheric dust loading is slightly more than 20 Tg, and has a small impact on the global climate. Such dust loading was diminished during the mid-Holocene (~6 thousand years ago; 6 ka) and the reduced dust induced a very slight global warming (~0.1 °C) but a cooling of the Northern Hemisphere by weakening the Atlantic meridional ocean circulation (AMOC). During the cold last glacial maximum (~21 ka), the atmospheric dust loading was ~2-3 times that of present day. Had not been this dust, the LGM climate would have been colder by ~2 °C and AMOC weaker by ~30%. Clearly, the snow-darkening effect of dust was dominative during this cold time period. For earlier periods with different continental configurations, the atmospheric dust loading also varied significantly. For 80 million years ago (Ma), the continents were dispersive and the total area of the continents was small, the atmospheric dust loading was only ~1.4 Tg. For 240 Ma, the continents clustered into a supercontinent and centered around the equator, the atmospheric dust loading ~21 Tg. For a continental configuration (130 Ma) that had an area in between 80 Ma and 240 Ma, the atmospheric dust loading was ~6.1 Tg. The dust had a cooling effect of <1 °C in all these three periods. For time periods earlier than 400 Ma when land vegetation had not evolved yet, the atmospheric dust loading could have been ~10 times of present day and cooled the climate by ~10 °C. However, such cooling effect disappeared and became a warming effect when the climate was entering a snowball Earth state, due to stronger and stronger snow-darkening effect.

Overall, there was more dust during a cold time period due to stronger winds, weaker hydrological cycle and more dust sources, and the dust had a warming effect to the climate. During the warm time periods, dust tended to have a cooling effect because there was too little snow and ice for the snow darkening by dust to be effective. There was also more dust during periods when the area of continents was larger and more clustered, due to drier land surface.

How to cite: Liu, Y., Lin, Q., Zhang, M., Liu, P., Zhang, J., and Liu, Z.: Evolution of Dust and Its Climatic Impact during Earth’s History, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4906, https://doi.org/10.5194/egusphere-egu22-4906, 2022.

EGU22-5081 | Presentations | CL1.1.1

Plate tectonic degassing estimated from full-plate models and age distributions of arc-related zircons

Trond H. Torsvik, Chloe M. Marcilly, Mathew Domeier, and Dana L. Royer

EGU22-6918 | Presentations | CL1.1.1

Influence of Dust on Climate during the late Palaeozoic ice age

Qifan Lin and Yonggang Liu

Dust in the atmosphere affects climate by directly absorbing and scattering solar radiation. In present days, most of dust is emitted from dry regions over North Africa and Arabian Peninsula. It has been shown that it impact on global mean surface temperature, African monsoon, the number of tropical cyclones over the Atlantic Ocean, ENSO variability and the strength of Atlantic meridional ocean circulation (AMOC). The climate of late Paleozoic ice age bears some similarity to late Cenozoic climate. However, late Paleozoic ice age was a period of continental convergence and supercontinents formation. On different continental configurations, the area of dry regions may vary considerably, so that dust emissions and atmospheric dust loading changed accordingly. As  expected, the impact of dust on climate during this period was also very different from that of present days. In this work, we use the fully coupled global climate model CESM1.2.2 to examine the influence of dust on climate during late Palaeozoic ice age. Dust aerosols simulated by bulk aerosol model alter atmospheric radiation through scattering and absorbing both shortwave and longwave radiation. Results show that during late Palaeozoic ice age, sources of dust were mainly distributed on the western continent in the subtropics. The total amount of the atmospheric dust loading was less than that of present days due to the smaller subtropical continental area. Such dust induced a significant cooling of surface temperature at low latitudes by altering radiation. Dust falling on southern hemisphere continents covered by ice and snow caused a rising of surface temperature.

How to cite: Lin, Q. and Liu, Y.: Influence of Dust on Climate during the late Palaeozoic ice age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6918, https://doi.org/10.5194/egusphere-egu22-6918, 2022.

EGU22-6804 | Presentations | CL1.1.1

Dynamics and variability of the Late Permian climate-carbon state in an Earth System Model

Daniel Burt, Tatiana Ilyina, and Thomas Kleinen

The Late Permian climate is the background state for the climate perturbations which lead to the
Permian-Triassic Boundary (~252 Ma). The Permian-Triassic Boundary mass extinction is well established as
the largest of Earth’s mass extinctions with an estimated 90% loss of species. Climate perturbations linked to
carbon emissions from Siberian Trap volcanism are attributed as the drivers of the mass extinction through
extreme temperature increases and changes in ocean circulation and biogeochemistry. Fully-coupled Earth
System Models are required to investigate the sensitivities and feedbacks of the system to these widespread
climate perturbations. The Late Permian climate is simulated with a modified version of the Max Planck
Earth System Model v1.2 similar to that used in the 6th -phase of the Coupled Model Intercomparison Project.
Geochemical and palaeobiological proxy data are used to constrain the boundary conditions of the modelled
climate state.
The simulated Late Permian climate state is characterised by a 100 year global mean 2 m surface air
temperature of 19.7°C, rising up to 37.7°C in the low-latitude continental interior. Prevailing 100 year global
mean total precipitation patterns indicate that the continental interior was largely arid from ~50°N to ~50°S and
a rainfall maximum of up to 6.5 mm day-1 is present at the equatorial boundary of the Tethys and Panthalassic
Oceans. Dynamic terrestrial vegetation in the model is dominated by woody single-stemmed evergreens and
soft-stemmed plant functional groups. The 100 year global mean surface ocean of the Late Permian illustrates
a warm-pool across the equatorial boundary between the Tethys and Panthalassic Oceans with a maximum
temperature of 31.7°C decreasing to temperatures as low as -1.9°C near the poles. Surface salinities vary
broadly across the global oceans with 100 year global mean values ranging from 21.9, in well flushed regions
of strong freshwater flux, to 49.2, in low-latitude regions of restricted exchange. Large-scale seasonal mixing
below 60°S in the Panthalassic Ocean dominates the global meridional overturning circulation. These model
data fit within the bounds represented by the available proxy data for the Late Permian. Additionally, I will
present first results of the ocean biogeochemical state in the Hamburg Ocean Carbon Cycle model with an
extended Nitrogen-cycle. I will also illustrate the results of our investigation into the influence of the Late
Permian monsoon variability on the terrestrial vegetation and ocean carbon cycles.

How to cite: Burt, D., Ilyina, T., and Kleinen, T.: Dynamics and variability of the Late Permian climate-carbon state in an Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6804, https://doi.org/10.5194/egusphere-egu22-6804, 2022.

EGU22-7520 | Presentations | CL1.1.1

Meridional temperature gradients during the past 250 million years: Proxies versus Models

Mengyu Wei, Jun Yang, Yongyun Hu, Yonggang Liu, Xiang Li, Xiujuan Bao, Jiaqi Guo, Jiawenjing Lan, Zhibo Li, Qifan Lin, Kai Man, Zihan yin, and Shuai Yuan

In this study, we investigate the meridional temperature gradients during the past 250 million years. We compare the differences between proxy data of oxygen isotopes and lithologic indicators and globally coupled atmosphere-ocean climate system model simulation results. Two climate models are employed, CESM1.2.2 and HadleyCM3. There are several significant differences between the model results and Scotese’s reconstruction and proxy data: 1) the tropical surface temperatures are usually higher in the model simulations than both Scotese’s reconstruction (Scotese 2016; Scotese et al. 2021) and proxy data (e.g., Huber and Caballero 2012, Song et al. 2019; Zhu et al. 2019), whereas the surface temperatures in high latitudes are usually lower; 2) the meridional temperature gradients in the model simulations are smaller in low latitudes but larger in the middle latitudes than Scotese’s reconstruction. These comparisons are helpful for paleoclimatology understanding and for future paleo-temperature reconstructions.

How to cite: Wei, M., Yang, J., Hu, Y., Liu, Y., Li, X., Bao, X., Guo, J., Lan, J., Li, Z., Lin, Q., Man, K., yin, Z., and Yuan, S.: Meridional temperature gradients during the past 250 million years: Proxies versus Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7520, https://doi.org/10.5194/egusphere-egu22-7520, 2022.

EGU22-10701 | Presentations | CL1.1.1

Climate evolution during the past 250 million years simulated by the Community Earth System Model

Xiang Li, Jiaqi Guo, Jiawenjing Lan, Qifan Lin, Shuai Yuan, Jun Yang, Yonggang Liu, and Yongyun Hu

Global climates have undergone tremendous fluctuations during the past 250 million years, primarily driven by variations in tectonic dynamics, atmospheric greenhouse gases, and solar irradiance. Paleoclimate modeling has offered a feasible approach to investigating secular climate change for such a long span of time deep in the past. Nevertheless, global mean surface temperatures (GMSTs) simulated by previous studies scarcely depict the trend of past climate change. In this study, using the Community Earth System Model version 1.2.2 (CESM1.2.2), we present an ensemble of snapshot simulations during the past 250 million years based on the reconstructed GMSTs. An energy balance analysis is carried out to explore and quantitatively describe the causes of temperature change for the past 250 million years. We find that different levels of global mean warming for the past 250 million years compared with the pre-industrial period predominantly results from relative increase in greenhouse gas emissivity (12.2 °C), with the changing paleogeography (5.6 °C) and solar constant (3.0 °C) playing secondary roles. It is highlighted that the individual effect of heat transport convergence varies inconspicuously in spite of considerable changes of paleogeography and mean climate states during this time. The simulations are potentially valuable resources for extensive studies including climate dynamics analysis in geological timescales and paleoclimate-proxy intercomparison.

How to cite: Li, X., Guo, J., Lan, J., Lin, Q., Yuan, S., Yang, J., Liu, Y., and Hu, Y.: Climate evolution during the past 250 million years simulated by the Community Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10701, https://doi.org/10.5194/egusphere-egu22-10701, 2022.

EGU22-7744 | Presentations | CL1.1.1

Hafnium-neodymium isotope evidence for enhanced weathering and tectonic-climate interactions during the Late Cretaceous

Pauline Corentin, Emmanuelle Pucéat, Pierre Pellenard, Michel Guiraud, Justine Blondet, Nicolas Freslon, Germain Bayon, and Thierry Adatte

Over million-year timescale the carbon cycle evolution is driven by mantle CO2 degassing (source) and by continental weathering that drawdowns atmospheric CO2 through silicate weathering reactions (sink). Based on a novel geochemical proxy of chemical weathering intensity (i.e. using measurements of Hf and Nd isotope ratios in clay-size fractions of sediments) and clay mineralogy, we discuss the links between tectonic, continental weathering and climate evolution during the late Cretaceous. That period records the very first step of the last greenhouse to icehouse transition and is concomitant to major uplift phases affecting the African and South-American margins.

Two sites along the South American Atlantic margin (ODP 356 and 1259) were targeted based on their relatively complete record of upper Cretaceous sediments. At Site 356, our results indicate the occurrence of enhanced chemical weathering during the Campanian and Maastrichtian following the uplift of the Southeastern Brazilian margin that promoted the establishment of more hydrolysing conditions.

At Demerara Rise (Site 1259), our data suggest a coupling between physical erosion and chemical weathering, which may be explained in this area by the presence of persistent hydrolysing conditions typical of equatorial climate and reduced tectonic activity. From the Turonian to the early Campanian, i.e. a period of relative tectonic quiescence, our data suggest that climate was likely the main driver controlling the evolution of chemical weathering intensity. By contrast, from the middle Campanian to Maastrichtian, we propose that mountain uplift, although moderate, induced a marked increase in chemical weathering intensity.

Together, this new data acquired at two 2 sites that encountered different regional climatic, geologic and tectonic conditions suggest that chemical weathering markedly intensified during the late Cretaceous and likely acted as a major sink for atmospheric CO2. While the onset of weathering increase at both sites appear to postdate the initiation of global temperature decrease, we suggest here that this process could have participated to accelerating or maintaining colder climate conditions at that time.

 

Key Words: late Cretaceous – paleoclimate – weathering – uplift - clay mineralogy – Hf-Nd isotope

How to cite: Corentin, P., Pucéat, E., Pellenard, P., Guiraud, M., Blondet, J., Freslon, N., Bayon, G., and Adatte, T.: Hafnium-neodymium isotope evidence for enhanced weathering and tectonic-climate interactions during the Late Cretaceous, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7744, https://doi.org/10.5194/egusphere-egu22-7744, 2022.

EGU22-6721 | Presentations | CL1.1.1

The Impact of Angiosperms Physiological Evolution on Earth Systems

Jiaqi Guo, Yongyun Hu, and Yonggang Liu

The physiological evolution of vegetation affects the interaction between vegetation and climate. Angiosperms have higher leaf vein density than all other plants throughout evolutionary history, contributing to higher transpiration capacities. However, the climatic response to changes in physiological functions of angiosperms has remained to be determined. Here, Community Earth System Model (CESM) version 1.2.2 and BIOME4 vegetation model are applied to simulate the world without angiosperms by reducing the maximum carboxylation rate (Vmax) to 1/4 (Boyce et al, 2009), in conditions of both fixed and non-fixed vegetation distribution. First, we maintain the pre-industrial vegetation distribution, the results illustrate that the world without angiosperms would have less productivity, higher global mean temperature, consisting with the results of Boyce and Lee (Boyce and Lee, 2010). In addition, the warmer southern hemisphere and colder northern hemisphere are identified, which are caused by the decrease of the strength of Atlantic Meridional Overturning Circulation (AMOC). Second, we consider changes of vegetation structure, the results show that temperature and precipitation would vary significantly locally, and the area of tropical forest would decline sharply in the world without angiosperms, which may affect biodiversity. The evolution of physiological functions of angiosperms influences climate and provides potential competitive advantages for angiosperms to dominate modern vegetation.

How to cite: Guo, J., Hu, Y., and Liu, Y.: The Impact of Angiosperms Physiological Evolution on Earth Systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6721, https://doi.org/10.5194/egusphere-egu22-6721, 2022.

EGU22-1078 | Presentations | CL1.1.1

Evolution of vegetation during the Cenozoic simulated by different land surface models

Delphine Tardif, Pierre Sepulchre, Fabien Condamine, and Thomas Couvreur

EGU22-10720 | Presentations | CL1.1.1

Eccentricity modulation of weathering and accumulation rates: non-intuitive, empirical relationship suggests links between orbital pacing and pCO2     

Paul Olsen, Sean Kinney, Clara Chang, Morgan Schaller, Jessica Whiteside, and Dennis Kent

The high frequency oscillations between wet and dry conditions plus the warmer temperatures when the Earth comes closest to the sun, might suggest weathering and hence accumulation rates should be highest during times of maximum eccentricity and maximum precessional variability in the tropics. But time series analysis of 20 Myr of continuous cores of tropical, lacustrine Late Triassic-age strata of the Newark Rift Basin (202–222 Ma) surprisingly show that that is not the case because accumulation rates are highest during the times of lowest precessional variance at the modes of the Mars–Earth (g4-g3) orbital cycle, when eccentricity is at a minimum.

            Three different methods of analysis reveal an accumulation pattern at variance with this intuitive model. 1) Tuning the depth-domain depth rank, color, and natural gamma data series to the 405 kyr, Venus–Jupiter (g2-g5) eccentricity metronome reveals oscillations in accumulation rates of ~20m to ~100m/Myr/cycle (within a total range of 70m – 250m/Myr). Spectral analysis reveals these oscillations occur with the same period (~1.8Myr) as the Mars–Earth modulation of precession for that time, with highs in accumulation rate occurring during lows in eccentricity. A weaker signal of the Mars–Earth (s4-s3) inclination cycle is also present at about 1/2 the period of the eccentricity cycle. 2) Application of the eTimeOpt method of sedimentation rate analysis reveals the same pattern and magnitudes of sedimentation rate variations in depth rank and color. 3) Spectral analyses of gamma and XRF elemental data from intervals of low- vs high-precessional variance show that significantly lower accumulation rated occurred during extended times of high- vs low-precessional variation.

            Accumulation rate oscillations in the Newark Rift Basin should be tracking weathering rates to supply the immense volumes of sediment involved in the accumulation rate variations. Such volumes could not be somehow stored in the highlands for hundreds of thousands of years, otherwise potentially shifting weathering and accumulation rates out of phase.

            The implication of these empirical data is that because pCO2 should be drawn down under higher weathering rates, and the phase of eccentricity modulation of precession is global, pCO2 should be oscillating in phase with the Mars–Earth eccentricity cycle. On the short-term, low-pCO2 should characterize times of low-precessional variability, evidently associated with high-accumulation rates, based on these empirical data, and not vice-versa as might be intuitively modeled. In turn, the oscillations in pCO2 would be expected to cause global temperature oscillations at the g4-g3 frequency. These non-intuitive results, suggesting a hitherto unanticipated relationship between orbital pacing of climate and pCO2, can be tested and further explored by continuous XRF elemental scanning of these cores, currently underway, and by collection of more densely sampled soil carbonate and leaf stomatal pCO2 proxy data, from proposed new cores. The mechanisms driving the relationships between these reproducible empirical data are, however, not obvious, but would seem to be related to the precession-scale variability of climate, not just the magnitude of greenhouse gas concentrations or temperatures.

 

 

 

 

 

 

 

How to cite: Olsen, P., Kinney, S., Chang, C., Schaller, M., Whiteside, J., and Kent, D.: Eccentricity modulation of weathering and accumulation rates: non-intuitive, empirical relationship suggests links between orbital pacing and pCO2     , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10720, https://doi.org/10.5194/egusphere-egu22-10720, 2022.

EGU22-11663 | Presentations | CL1.1.1

Modeling the Impact of Paleogeography on Cretaceous Ocean Deoxygenation

Yannick Donnadieu, Nina Papadomanolaki, Marie Laugie, Anta Sarr, and Jean-Baptiste Ladant

Oceanic Anoxic Events (OAEs) were geologically short-lived events of widespread ocean deoxygenation and marine organic carbon burial and occurred mostly during the Cretaceous period. The development of OAEs is largely attributed to the impact of massive volcanism on climate and marine biogeochemistry; however, the lack of similar events during other carbon-cycle perturbations suggests additional mechanisms. We use the IPSL-CM5A2 Earth System Model to assess the role of changing paleogeography in priming the Cretaceous Ocean for large-scale decrease in intermediate and deep oxygen concentrations. We focus on three time-slices that present differences in potential gateway (e.g. the Central American Seaway) depth and basin configuration (e.g. the North Atlantic): the Aptian age (~120 Ma), the Cenomanian-Turonian boundary (~94 Ma) and the Maastrichtian age (~70 Ma). This set of simulations illustrates the impact of paleogeography on global circulation and its consequences for intermediate and deep water oxygenation. We also show results for two different atmospheric CO2 concentrations (2x and 4x pre-industrial) to study the additional influence of differing climatic states on oxygenation and primary productivity, and their importance relative to ocean dynamics.

How to cite: Donnadieu, Y., Papadomanolaki, N., Laugie, M., Sarr, A., and Ladant, J.-B.: Modeling the Impact of Paleogeography on Cretaceous Ocean Deoxygenation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11663, https://doi.org/10.5194/egusphere-egu22-11663, 2022.

EGU22-3321 | Presentations | CL1.1.1

Modeling the evolution of central Asian drylands during the Cenozoic

Ran Zhang, Zhongshi Zhang, Dabang Jiang, Gilles Ramstein, Guillaume Dupont-Nivet, and Xiangyu Li

The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land–sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.

How to cite: Zhang, R., Zhang, Z., Jiang, D., Ramstein, G., Dupont-Nivet, G., and Li, X.: Modeling the evolution of central Asian drylands during the Cenozoic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3321, https://doi.org/10.5194/egusphere-egu22-3321, 2022.

EGU22-10287 | Presentations | CL1.1.1

Long-term increase in precipitation intermittency and intensity at Paleogene mid latitudes 

Jacob Slawson and Piret Plink-Bjorklund

Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Early Eocene by 2150 CE, suggesting that we are effectively reversing a more than 50-million-year cooling trend in less than two centuries. Terrestrial records of rivers and floodplains from Paleogene sedimentary basins in the US Western interior and Europe indicate an increase in flash floods and droughts at paleo-mid latitudes, indicating increased precipitation intensity and intermittency. In the Uinta Basin, Utah magnetostratigraphic analyses, absolute age dates, and biostratigraphy allow the reconstruction of changes in hydroclimate from the Early Paleocene, to the Paleocene-Eocene Thermal Maximum (PETM), and through the Early Eocene Climatic Optimum (EECO). Here we observe that the largest shifts in hydroclimate are not linked to the PETM but rather occur during the warm Late Paleocene and then at the end of the EECO. This is indicated by the river sedimentary record that shows a shift from normal rivers, such as are characteristic at mid-latitudes today, to flood-prone rivers in late Paleocene. The rivers shifted back to normal at the end of the EECO. Coeval changes are observed in floodplain paleosols where the late Paleocene and early Eocene paleosols indicate sustained droughts and intermittent seasonal rains. At the PETM there is no change in the state of hydroclimate, but rather a further intensification of floods and droughts. Comparison to other terrestrial basins at mid-latitudes shows similar patterns. These results show that the most dramatic shifts in hydroclimate were not linked to the largest amplitude of atmospheric drivers at the PETM, but rather suggest a threshold-driven relationship between the atmospheric drivers and hydroclimate. This may suggest that significant changes in hydroclimate are to be expected already before 2150 CE. 

How to cite: Slawson, J. and Plink-Bjorklund, P.: Long-term increase in precipitation intermittency and intensity at Paleogene mid latitudes , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10287, https://doi.org/10.5194/egusphere-egu22-10287, 2022.

EGU22-919 | Presentations | CL1.1.1

Polar amplification of early Eocene orbital climate variability

Chris Fokkema, Tobias Agterhuis, Danielle Gerritsma, Claudia Agnini, Peter Bijl, Joost Frieling, Matthew Huber, Francien Peterse, and Appy Sluijs

EGU22-1701 | Presentations | CL1.1.1

Variable Early Eocene continental hydroclimate in Central Europe? 

Clemens Schmitt, Iuliana Vasiliev, Alfredo Martínez-García, and Andreas Mulch

Predicted future climate scenarios share similar characteristics with the Eocene ‘greenhouse’ period. However, short-term Early Eocene terrestrial climate variability is still poorly constrained mainly due to the rarity of adequately resolved climate archives. This lack of information restricts not only the evaluation of past continental climate conditions but additionally limits regional climate modelling efforts but also the validation of model outputs. Here, we present highly-resolved biomarker-based (bacterial membrane lipid and leaf wax) paleoclimate data from the UNESCO World Heritage Site Messel Fossil Pit (Germany) that cover an interval of ca. 640 ka. The drilled Messel paleolake succession, characterized by finely laminated and frequently varved black pelites (referred to as ‘oil shale’) represent a regional climate and environmental archive from the latest Early to Middle Eocene (~48.0-47.4 Ma) of western Central Europe. Downcore mean annual air temperature (MAAT) reconstructions inferred from bacterial-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs) show a long-term cooling trend and range from 14 to 22°C. High-resolution sampling within the basal and middle core interval reveal several short-term negative temperature excursions of 4-5°C, respectively. Moreover, we measured compound-specific δ2H and δ13C of excellently preserved odd carbon numbered mid- and long-chain leaf wax n-alkanes in order to estimate past regional hydroclimatic conditions. δ2H values of terrestrial long- and aquatic mid-chain n-alkanes show exceptional variations of up to 45‰ and 60‰, respectively. In contrast, δ13C values of long-chain n-alkanes are within 5‰ (-28‰ to -33‰) while mid-chain δ13C values vary by 11‰, ranging between -26‰ and -37‰. Our results indicate that the Early to Middle Eocene temperature history of central western Europe, particularly on short geological timescales was much more variable than previously assumed. We recognize two abrupt shifts in MAAT that coincide with lower δ2H values and therefore may point to either wetter climate conditions or changed atmospheric moisture trajectories. We emphasize that the long-term decline in estimated MAAT towards the top of the Messel section has to our best knowledge not been quantified from any time-equivalent terrestrial archive in Central Europe, but resembles Early Eocene cooling patterns well-documented from the global oceans.

How to cite: Schmitt, C., Vasiliev, I., Martínez-García, A., and Mulch, A.: Variable Early Eocene continental hydroclimate in Central Europe? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1701, https://doi.org/10.5194/egusphere-egu22-1701, 2022.

EGU22-2399 | Presentations | CL1.1.1 | Highlight

Reconciling South Asian Monsoon Rainfall and Wind Histories

Anta-Clarisse Sarr, Yannick Donnadieu, Clara Bolton, Jean-Baptiste Ladant, Alexis Licht, Frédéric Fluteau, Marie Laugié, Delphine Tardif, and Guillaume Dupont-Nivet

Cenozoic evolution of South Asian Monsoon and mechanisms driving changes recorded in the geological record remain highly debated. An intensification of monsoonal rainfall recorded in sediment archives from the earliest Miocene (23-20 million years ago, Ma) is generally attributed to Himalayan uplift. However, Indian Ocean paleorecords place the onset of strong monsoons around 13 Ma, linked to strengthening of the Somali Jet that forces Arabian Sea upwelling.  In this contribution we reconcile these divergent records using Ocean-Atmosphere and ocean biogeochemistry models. Our results show that factors forcing monsoon circulation versus rainfall are decoupled and diachronous : Asian topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean-atmosphere circulation. Yet the uplift of East African and Middle Eastern topography played a pivotal role in the establishment of modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiate in response to the emergence of the Arabian Peninsula. Our results emphasize a polygenetic history of the South Asian Monsoon with multiple paleogeographic controls: although elevated rainfall seasonality was likely a persistent feature since the India-Asia collision in the Paleogene, the modern-like monsoonal atmospheric circulation was only reached recently, in the late Neogene.

How to cite: Sarr, A.-C., Donnadieu, Y., Bolton, C., Ladant, J.-B., Licht, A., Fluteau, F., Laugié, M., Tardif, D., and Dupont-Nivet, G.: Reconciling South Asian Monsoon Rainfall and Wind Histories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2399, https://doi.org/10.5194/egusphere-egu22-2399, 2022.

EGU22-10815 | Presentations | CL1.1.1

South Atlantic deep-sea temperatures across the onset of the Early Eocene Climatic Optimum based on clumped isotope thermometry

Tobias Agterhuis, Martin Ziegler, Bas L. P. Koene, Lea de Vries, Anne Roozendaal, and Lucas J. Lourens

Reconstructing deep ocean temperature is important to infer deep water mass structure and hence ocean circulation patterns in the past. The late Paleocene-early Eocene experienced the warmest climates of the Cenozoic, with highly elevated CO2 levels and no ice sheets on the continents [1,2]. Benthic foraminiferal δ18O records suggest relatively stable deep ocean conditions on long time scales (>100 kyr) in this hothouse [2–4]. However, interpretations from benthic δ18O records are complicated by influences of factors other than temperature, such as the isotope composition of the seawater (δ18Osw), pH, and species-specific physiological effects [5,6]. Carbonate clumped isotope thermometry (Δ47) has the major advantage that it is independent of the isotope composition of the fluid source, and is not measurably affected by other non-thermal influences [7–10]. Early Cenozoic clumped isotope reconstructions from the North Atlantic have revealed surprisingly large deep-sea temperature swings under hothouse conditions [11]. Extreme warming is recorded at the onset of the Early Eocene Climatic Optimum (EECO) [11]. To explore the spatial extent of these deep-sea temperature changes, we reconstructed early Eocene Δ47-based deep-sea temperatures from the South Atlantic Ocean, a location that is considered to capture a global signal [2–4]. We find similar deep-sea temperatures as those from the North Atlantic. Cooler temperatures of ~12 °C stand out in the interval (54–52 Ma) before the peak warmth of the EECO (52–50 Ma) of ~20 °C. This result overthrows the classic view of a gradual early Eocene warming trend based on benthic δ18O records, at least for the deep Atlantic Ocean. Our findings raise new questions on the regions of deep water formation, changes in deep ocean circulation, and the driving mechanisms in the early Cenozoic hothouse.

References
[1] Anagnostou, E. et al. (2016). Nature533(7603), 380-384.
[2] Zachos, J. et al. (2001). Science292(5517), 686-693.
[3] Lauretano, V. et al. (2018). Paleoceanography and Paleoclimatology33(10), 1050-1065.
[4] Westerhold, T. et al. (2020). Science369(6509), 1383-1387.
[5] Ravelo, A. C., & Hillaire-Marcel, C. (2007). Developments in marine geology1, 735-764.
[6] Pearson, P. N. (2012). The Paleontological Society Papers18, 1-38.
[7] Ghosh, P. et al. (2006). Geochimica et Cosmochimica Acta70(6), 1439-1456.
[8] Tripati, A. K. et al. (2015). Geochimica et Cosmochimica Acta166, 344-371.
[9] Guo, W. (2020). Geochimica et Cosmochimica Acta268, 230-257.
[10] Meinicke, N. et al. (2020). Geochimica et Cosmochimica Acta270, 160-183.
[11] Meckler, A. N. et al. (in revision).

How to cite: Agterhuis, T., Ziegler, M., Koene, B. L. P., de Vries, L., Roozendaal, A., and Lourens, L. J.: South Atlantic deep-sea temperatures across the onset of the Early Eocene Climatic Optimum based on clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10815, https://doi.org/10.5194/egusphere-egu22-10815, 2022.

EGU22-10380 | Presentations | CL1.1.1

Partitioning meridional heat transport in Early Eocene Climatic Optimum model simulations

Fanni Dora Kelemen and Bodo Ahrens

The meridional heat transport is primarily governed by the geometry between the Earth and the Sun and it has been shown in previous studies that it is nearly invariant in different climates. Nevertheless, the processes, which contribute to the whole transport, do not stay invariable, but their changes compensate each other. Thus, the changes in the various transport processes give an insight into the climate system and its changes in different conditions, such as the high CO2 concentrations of the Early Eocene Climatic Optimum (EECO).

In our work we investigate the meridional heat transport and its elements in climate model simulations from DeepMIP focusing on the EECO. The meridional heat transport is divided into atmospheric and ocean heat transport. The atmospheric heat transport is further divided into moist and dry energy transport and also into transport by the meridional overturning circulation, transient eddies and stationary eddies. Annual and seasonal changes are compared in the preindustrial control simulation, in the 1xCO2 simulation and in simulations with high CO2 concentration values (3xCO2, 4xCO2, 6xCO2). We found that in a warmer climate, where the hydrological cycle is expected to be stronger, the transport of the meridional overturning circulation at the tropics, so the circulation of the Hadley cell, is more intense. Also, at the subtropics the energy transport of monsoon systems and at the mid-latitudes the energy transport of cyclones and anticyclones is different than in the control climate.

 

How to cite: Kelemen, F. D. and Ahrens, B.: Partitioning meridional heat transport in Early Eocene Climatic Optimum model simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10380, https://doi.org/10.5194/egusphere-egu22-10380, 2022.

EGU22-5621 | Presentations | CL1.1.1

Spatial heterogeneity of the Late Miocene Biogenic Bloom

Quentin Pillot, Baptiste Suchéras-Marx, Anta-Clarisse Sarr, Clara Bolton, Jean-Baptiste Ladant, and Yannick Donnadieu

The late Miocene and early Pliocene is marked by a major
oceanographic and geological event called the Late Miocene Biogenic
Bloom (LMBB). This event is characterized by high accumulation rates of
opals from diatoms and high calcite accumulation rates from calcareous
nannofossils and planktic foraminifera. The LMBB extends over several
million years and is present in the Pacific, Atlantic and Indian Oceans. Two
hypotheses have emerged from the literature to explain this event: a
global increase in the supply of nutrients to ocean basins through chemical
alteration of the continents and/or a major redistribution of nutrients in the
oceans. The objective of this study is to provide a more comprehensive
look at the temporal and geographical aspects of the LMBB. We have
compiled ocean drilling data (ODP-IODP) covering the late Miocene and
early Pliocene. This compilation contains sedimentation rates as well as
CaCO3, opal and terrigenous accumulation rates. After a careful screening
of the database, checking that all data are on the same time scale, we first
work on global trends of sedimentation and biogenic production before
going into more details. For instance, we show that the magnitude of the
Biogenic Bloom strongly varied between the three oceanic basins.
Normalization to a post-LMBB state allows comparison of rates of increase
in CaCO3 accumulation in different geographical areas (grouping several
sites). A very strong LMBB signature is present in oceanic area bordering
the western side of Australia. In the Atlantic Ocean, it is mainly present
near the equator and over South Africa. The LMBB signature is less
pronounced in the Indian Ocean but remains trackable near the northern
coasts of the basin. Moreover, it is also heterogeneous in terms of the
mineralogy produced and deposited in the deep ocean between regions.
For example, in the equatorial eastern Pacific, the LMBB signature is
present in the silica accumulation term but not in carbonates accumulation
one. Outputs from coupled ocean/atmosphere models (IPSL-CM5A2) using
late Miocene paleogeography and integrating a marine biogeochemistry
module (PISCES) have been gathered and will be discussed in regard to
our database.

How to cite: Pillot, Q., Suchéras-Marx, B., Sarr, A.-C., Bolton, C., Ladant, J.-B., and Donnadieu, Y.: Spatial heterogeneity of the Late Miocene Biogenic Bloom, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5621, https://doi.org/10.5194/egusphere-egu22-5621, 2022.

EGU22-2042 | Presentations | CL1.1.1

Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations

André Bahr, Stefanie Kaboth-Bahr, Christian Stepanek, Maria Carolina Amorim Catunda, Cyrus Karas, Martin Ziegler, Ángela García-Gallardo, and Patrick Grunert

The intensification of the Northern Hemisphere glaciations at the end of the Pliocene epoch represents one of the most substantial climatic shifts during Cenozoic. Paradoxically, sea surface temperatures in the high latitude North Atlantic Ocean increased between 2.9–2.7 Ma, against a background of global cooling and declining atmospheric pCO2. To investigate the origin of this high latitude warming, we obtained sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. In fact, we find evidence for enhanced production of Mediterranean Outflow Water during the mid-Pliocene to late Pliocene. We argue that the injection of this warm water on intermediate levels drove a sub-surface heat channel into the high-latitude North Atlantic where it warmed the sea surface. We further used Earth System Models to numerically constrain the impact of enhanced Mediterranean Outflow Water production on the northward heat transport within the North Atlantic. In accord with the proxy evidence, the numerical model results show the formation of a sub-surface channel that funneled heat from the subtropics into the high latitude North Atlantic. We further suggest that warming of the North Atlantic realm by this mechanism might have substantially delayed ice sheet growth at the end of the Pliocene.

How to cite: Bahr, A., Kaboth-Bahr, S., Stepanek, C., Amorim Catunda, M. C., Karas, C., Ziegler, M., García-Gallardo, Á., and Grunert, P.: Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2042, https://doi.org/10.5194/egusphere-egu22-2042, 2022.

EGU22-2957 | Presentations | CL1.1.1

Atmospheric variability in the Northern Hemisphere winter in a warm past and a future climate

Arthur Oldeman, Michiel Baatsen, Anna von der Heydt, Aarnout van Delden, and Henk Dijkstra

The Northern Annular Mode (NAM) is the leading mode of atmospheric climate variability in the middle and high Northern latitudes in the present-day climate. Its most prominent regional expression is the North Atlantic Oscillation (NAO), a mode of variability that is well-known and has a strong influence on North Atlantic weather patterns. According to the IPCC AR6 WGI report, the current generation of climate models are ‘skillful’ in simulating the spatial features and variance of the historical and present-day NAM/NAO. However, what kind of NAM or NAO patterns can we expect in a warm future climate?

To answer this question, we have performed equilibrium climate simulations of a warm ‘future’ as well as a warm past climate. Specifically, we have simulated the mid-Pliocene climate, a warm (~400 ppm CO2) geological period approximately 3Ma ago, using a global coupled climate model (CESM1.0.5). Our simulations compare well to higher latitude sea-surface temperature reconstructions. We have performed sensitivity studies using a pre-industrial and a mid-Pliocene geography, as well as two levels of radiative forcing, as a part of intercomparison project PlioMIP2. But the question remains, to what extent can we treat the mid-Pliocene as an ‘analog’ for a future warm climate?

Looking at Northern hemisphere winter (DJF) sea-level pressure data, we find that the annular ‘belts of action’ move poleward partially due to increase in CO2, but mainly due to the mid-Pliocene boundary conditions. Over the North Pacific Ocean, sea-level pressure variability slightly increases with CO2, but greatly reduces due to the mid-Pliocene geography. The NAM seems to behave more ‘annular’ and less ‘sectoral’ or regional due to the mid-Pliocene climate boundary conditions. We will focus on the mechanisms that explain the differences between the past and future simulations.

How to cite: Oldeman, A., Baatsen, M., von der Heydt, A., van Delden, A., and Dijkstra, H.: Atmospheric variability in the Northern Hemisphere winter in a warm past and a future climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2957, https://doi.org/10.5194/egusphere-egu22-2957, 2022.

EGU22-5586 | Presentations | CL1.1.1

Mid-Pliocene North American Monsoon in Weather Resolving Coupled Simulations

Mary Grace Albright, Ran Feng, Jiang Zhu, Bette Otto-Bliesner, Hui Li, and Tripti Bhattacharya

The North American Southwest (SW NA) has recently experienced periods of extreme drought, largely due to an increased intensity in evaporation. Yet, there remains large uncertainty in the predicted future changes of precipitation over this region. As a result, the future of SW NA hydroclimate remains uncertain.  The North American Monsoon (NAM) is an atmospheric circulation feature of SW NA hydroclimate that is generated by interactions between topography and moisture surge from the Gulf of California and the Gulf of Mexico.  Previous research has shown a weakened NAM in response to elevated levels of atmospheric CO2.  However, when analyzing proxy paleoclimate reconstructions during the Pliocene, various records suggest wetter conditions during that time.  We use the mid-Pliocene (3.3 – 3.0 Millions of years ago) as an analog for ongoing climate change because this interval featured topography, geography, and biome assemblages similar to today, but a warmer global mean temperature by 2 - 4 °C compared to pre-industrial, and a sustained 400 ppm CO2.  Here we are testing whether a high resolution simulation (25 km) can better capture the NAM and provide different sensitivity to boundary conditions compared to low resolution (100 km) simulations, using the same Community Earth System Model.  Increased resolution has been shown to improve the representation of features within the NAM for simulations of the present.   Our pre-industrial simulations display a more extensive monsoon region with high spatial resolution, which indicates a dependency of simulated NAM on resolving topographic features such as the Rockies, Basin and Range, and Gulf of California, all of which can only be captured at high spatial resolutions.  Simulations of the mid-Pliocene displayed weakened NAM precipitation along the west coast of the southwestern North America at a low resolution when compared to the pre-industrial run.  Yet, this weakening signal is limited to the Pacific side of the orographic slopes in the high resolution simulation, with the rest of the monsoon region featuring increased precipitation.  Ongoing work will explore the sources for this resolution dependency, and will quantify contributions of mesoscale systems, such as tropical and extratropical cyclones, to precipitation in the monsoon region.

How to cite: Albright, M. G., Feng, R., Zhu, J., Otto-Bliesner, B., Li, H., and Bhattacharya, T.: Mid-Pliocene North American Monsoon in Weather Resolving Coupled Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5586, https://doi.org/10.5194/egusphere-egu22-5586, 2022.

EGU22-6006 | Presentations | CL1.1.1

Drivers and consequences of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation

Julia Weiffenbach, Michiel Baatsen, and Anna von der Heydt

The mid-Pliocene warm period (mPWP, ~3.3 – 3 Ma) is the most recent geological period with a CO2 concentration similar to the present day (~400 ppm). The Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) focuses on the KM5c time slice (3.205 Ma), giving insight into the climate dynamics of this period. Sea surface temperature (SST) proxies indicate amplified warming over the North Atlantic in the mPWP with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC). Zhang et al. (2021) reported a stronger mPWP AMOC in all the PlioMIP2 simulations but found no consistent relation to either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs. We therefore look further into the drivers and consequences of a stronger AMOC in the mPWP compared to pre-industrial simulations.

Within the PlioMIP2 ensemble, we find that all model simulations with a closed Bering Strait and Canadian Archipelago show strongly reduced freshwater transport from the Arctic Ocean into the North Atlantic. The resulting increase in sea surface salinity in the subpolar North Atlantic and Labrador Sea stimulates deepwater formation in these areas. The stronger AMOC is therefore primarily a response to the closure of the Arctic gateways. We also look at the different components of the Atlantic OHT, associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mPWP, it is partly compensated by a reduced gyre component. Our results point towards a complex interplay between atmospheric and oceanic processes and indicate that considering these components separately allows for a better understanding of the climatic response to the AMOC strength.

How to cite: Weiffenbach, J., Baatsen, M., and von der Heydt, A.: Drivers and consequences of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6006, https://doi.org/10.5194/egusphere-egu22-6006, 2022.

EGU22-11222 | Presentations | CL1.1.1

South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene transition from clumped isotope thermometry

Elena Domínguez Valdés, Ilja Kocken, Tobias Agterhuis, Inigo Müller, Noa Bode, Dirk Kroon, Lucas Lourens, and Martin Ziegler

The reconstruction of deep-ocean temperatures is key in the study of the different climate states in the geological past. Reconstructions covering the Pliocene-Pleistocene transition shed light on the global climatic change that followed the mid-Pliocene warm period and culminated in full glaciation of the Northern Hemisphere.

Global δ18O records measured on seafloor dwelling foraminifera constitute the backbone of our understanding of the climatic trends and transitions of the last 65 million years [1,2]. These records suggest that the glacial intensification over the last 2.8 Ma experienced the onset of Quaternary-style ice age cycles and the progression towards a more deterministic climate system increasingly sensitive to orbital forcings. Deep-sea temperature variability across this time is thought to have stayed in a 4ºC range with near-freezing temperatures occurring at every glacial maximum, especially after the Mid-Pleistocene transition [2,3]. However, temperature signals based on carbonate δ18O data are built upon uncertain assumptions of non-thermal factors such as those regarding the isotopic composition of the ancient seawater.

Carbonate clumped thermometry (𝛥47) is based on thermodynamic principles that determine the ordering of isotopes within the carbonate crystal lattice [4]. It is independent of the fluid composition. 𝛥47 thermometry has recently been used to anchor Mg/Ca records of the Miocene while revealing a comparatively warm deep ocean [5].

Here we present 𝛥47-based deep-sea temperature constraints across the Pliocene-Pleistocene transition obtained from benthic foraminifera of ODP Site 1264 in the South Atlantic Ocean. In combination with benthic δ18O analyses, we furthermore interpret our measurements into global ice volume and ocean circulation changes in the Atlantic Basin across the major onset of the Northern Hemisphere Glaciation.

[1] Zachos, J., et al. (2001), Science 292, 686-693.

[2] Westerhold, T., et al. (2020), Science, 369, 1383–1387,

[3] Elderfield, H., et al. (2012) Science, 337(6095), 704-709.

[4] Eiler, J.M. (2007), Earth Planet. Sci. Lett. 262, 309-327.

[5] Modestou, S. E., et al. (2020) Paleoceanography and Paleoclimatology 35, e2020PA003927.

How to cite: Domínguez Valdés, E., Kocken, I., Agterhuis, T., Müller, I., Bode, N., Kroon, D., Lourens, L., and Ziegler, M.: South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene transition from clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11222, https://doi.org/10.5194/egusphere-egu22-11222, 2022.

CL1.1.3 – Interglacial diversity

EGU22-2443 | Presentations | CL1.1.3 | Highlight

All interglacials are different, but some are more different than others

Chronis Tzedakis, David Hodell, Christoph Nehrbass-Ahles, and Eric Wolff

Examination of the palaeoclimate record of the last 800 kyr has revealed a large diversity among interglacials in terms of their duration, structure and intensity.  Interglacials may be classified as either short (mean duration 13 kyr) or long (mean duration 28 kyr).  The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks: the longest interglacials are characterized by the obliquity peak lagging the first precession minimum by 10±2 kyr and leading the second precession minimum by a similar amount; thus the first boreal summer insolation minimum occurs at the time of maximum obliquity, which overrides the increase in precession and prevents glacial inception associated with a decline in summer insolation.  The phasing of precession and obliquity also determines the structure of an interglacial, leading to two main categories: (1) shorter interglacials characterized by rapid deglaciation and an early temperature optimum, usually followed by a decline; and (2) longer interglacials characterized by protracted deglaciation and the persistence of interglacial values over two insolation peaks, with the interglacial peak occurring in the second insolation maximum.  With respect to intensity, a broad feature is that interglacials before the Mid-Brunhes Event (MBE; 430 ka) appear weaker (cooler, higher δ18Obenthic, atmospheric CO2 lower than pre-industrial concentrations).  The strongest interglacials occurred after the MBE, although MIS7e and MIS7c-a are closer in intensity to pre-MBE interglacials.  Of particular interest is MIS 11c, one of the most unusual Quaternary interglacials.  Its features include: (i) a high sea-level highstand attained under modest insolation forcing; (ii) a long duration extending over two insolation peaks; (iii) persistence of relatively stable atmospheric CO2 concentrations, remaining in the range 270-282 ppm for a 24 kyr period; and (iv) a decoupling between high CO2 and high sea level in the early part of the interglacial that is unique in the last 800 kyr.  Although some of these features are also encountered in other interglacials, their combination with strong interglacial intensity is unique to MIS 11c and appears to be a function of the high CO2concentrations from the beginning of the interglacial.

How to cite: Tzedakis, C., Hodell, D., Nehrbass-Ahles, C., and Wolff, E.: All interglacials are different, but some are more different than others, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2443, https://doi.org/10.5194/egusphere-egu22-2443, 2022.

EGU22-6616 | Presentations | CL1.1.3

A southern Portuguese margin perspective of Marine Isotope Stage 47 – an interglacial in the 41 kyr world

Antje H. L. Voelker, Teresa Rodrigues, Samanta Trotta, Maria Marino, and Henning Kuhnert

In order to understand interglacial climate variability we also need to study interglacial periods prior to the Mid-Pleistocene Transition, i.e. within the 41 kyr world. Early Pleistocene interglacial periods, in particular from the interval directly preceding the onset of the Mid-Pleistocene Transition, provide ideal study cases since interglacial atmospheric carbon dioxide levels during that period appear to have been similar to or only slightly higher than during the warmest interglacials of the last 800 ka. Here we present the first results from a high-resolution, multi-proxy study of interglacial Marine Isotope Stage (MIS) 47 (1424-1452 ka) at IODP Site U1387 (36°48´N 7°43´W), drilled into the Faro Drift on the southern Portuguese margin at 559 m water depth. Nowadays, surface waters near Site U1387 originate from the subtropical gyre, whereas the intermediate-depth Mediterranean Outflow Water (MOW) is encountered at the seafloor. For our study, we use the stable isotope data of planktonic foraminifera species G. bulloides and G. ruber white and benthic foraminifera species P. ariminensis and C. pachyderma, biomarker-derived sea-surface temperatures (SST), the weight percentage of the sand fraction, and microfossil evidence.

Following a rapid transition, interglacial conditions were quickly established in the surface waters with SST at levels near or above 24°C, sometimes even exceeding 25°C, throughout much of MIS 47. Those are the warmest SST so far observed for the Pleistocene at that location, being more than three degrees warmer than modern SST. The common occurrence of tropical species in the planktonic foraminifera fauna hints to a persistent contribution of tropical waters to the surface waters and thus probably the northward expansion and/or intensification of the North Atlantic's subtropical gyre. The MOW, on the other hand, experienced an extended period of poor ventilation, most likely associated with low oxygen levels, as indicated by the extremely low benthic carbon isotope values and the occurrence of gypsum crystals in the sediments that formed when the pyrite in the sediments was oxidized after the cores were opened. Following evidence from younger interglacials, this MOW signal should be linked to reduced ventilation and overturning in the Mediterranean Sea as consequence of increased freshwater input caused by an intensified North African monsoon. The benthic δ18O record of MIS 47 indicates a three phased interglacial period with a minimum separating two maxima. On a subtle level, this phasing might also exist in the surface water records. This and potential causes need to be explored further in the future, when all high-resolution data is available. Overall, the Site U1387 records confirm MIS 47 as a "super"-interglacial, much more so than MIS 31, on the southern Portuguese margin. Insights from this warm interglacial and associated oceanographic conditions and changes in the planktonic and benthic microfossil floras and faunas might provide hints on how future warming in those waters could impact the regional ecosystems.

How to cite: Voelker, A. H. L., Rodrigues, T., Trotta, S., Marino, M., and Kuhnert, H.: A southern Portuguese margin perspective of Marine Isotope Stage 47 – an interglacial in the 41 kyr world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6616, https://doi.org/10.5194/egusphere-egu22-6616, 2022.

EGU22-3148 | Presentations | CL1.1.3

The Early-Middle Pleistocene interglacials in the Iberian margin

Maria Fernanda Sanchez Goñi, Dulce Oliveira, César Morales-Molino, Stéphanie Desprat, Josue M. Polanco-Martinez, David Hodell, Filipa Naughton, and Teresa Rodrigues

Interglacials older than 450,000 years ago (ka) are still poorly documented at regional and global scale limiting our knowledge of the wide range of their potential variability and the understanding of the causes of such diversity. Here we present δ18O benthic foraminifera measurements along with sea surface temperature reconstructions and pollen data from IODP site U1385, collected during Expedition 339 « Mediterranean Outflow » on the southwestern Iberian margin, for the Early-Middle Pleistocene interglacials MIS 19, 17, 15 and 13 (~800 to 400 ka). The recorded vegetation and climate changes on land have been directly compared with changes in the eastern North Atlantic subtropical gyre and the global ice volume. This comparison reveals a different structure in the evolution of the Mediterranean forest during these interglacials. The highest forest development occurred during MIS 19e and 15e but in the middle part of MIS 13 (MIS 13c). In contrast with MIS 19, 15 and 13 marked by three more or less similar Mediterranean forest expansions, MIS 17 was characterised by one strong expansion in its middle part (MIS 17c), the strongest of the last 800,000 years, occurring just before the end of the Middle Pleistocene Transition, i.e. the establishment of the strong 100-kyr glacial cycles at ~700 ka.  The duration of the first forested phase was also variable depending on the interglacial with a length of ~12,000 years during MIS 19e and 15e, ~9,000 years for MIS 13c and as long as 16,000 years for MIS 17c. Interestingly, two Mediterranean forest expansions are recorded during two phases of ice growth, MIS 19b and 15b, indicating once more the decoupling between the evolution of global ice volume and the southern European environments. The comparison of the U1385 pollen record, located below 40°N, with sequences above 40°N, for example the Lake Orhid pollen record, shows that the structure and magnitude of the interglacials are different below and above this latitude. At Montalbano Jonico, southern Italy at 40°N, the forest expansion is also very strong (80%) during MIS 17 contrasting with the limited development in Lake Orhid. At this site, MIS 19 is further marked by a strong forest development contrasting with the limited expansion of the Mediterranean forest in SW Iberia.

How to cite: Sanchez Goñi, M. F., Oliveira, D., Morales-Molino, C., Desprat, S., Polanco-Martinez, J. M., Hodell, D., Naughton, F., and Rodrigues, T.: The Early-Middle Pleistocene interglacials in the Iberian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3148, https://doi.org/10.5194/egusphere-egu22-3148, 2022.

Numerous studies have been made on paleoclimate and paleovegetation reconstructions and simulations of the past interglacials. However, systematical analysis of the global patterns of the correlation between vegetation pattern and astronomical forcing as well as CO2 between different interglacials is rare. Given the distinct differences in orbital configurations and climate/vegetation variations between MIS-11 and MIS-13, we performed two sets of transient simulations using LOVECLIM 1.3, one driven by insolation change only, and another one by changes in both insolation and CO2. These simulations allow us to investigate the relative effect of astronomical forcing and CO2 on global and regional vegetation changes during these two interglacials. Our results show that the effects of precession and obliquity on vegetation depend strongly on regions, and the simulated results are in good agreement with vegetation reconstructions at key regions. The vegetation response differs widely between MIS-11and MIS-13, which is mainly caused by the difference in their astronomical configurations, and the difference in CO2 concentration between these two interglacials plays a minor role. In addition to the effect of precession and obliquity, our simulations are also able to capture the half precession signal (~ 10 ka) in the climate and vegetation changes in the tropical regions in response to the tropical insolation.

How to cite: Su, Q., Lyu, A., Wu, Z., and Yin, Q.: Diverse manifestations of the impact of astronomical forcing and CO2 on climate and vegetation changes during MIS-11 and MIS-13, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4354, https://doi.org/10.5194/egusphere-egu22-4354, 2022.

EGU22-8018 | Presentations | CL1.1.3

Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition

João Ballalai, Thiago Santos, Rodrigo Nascimento, Igor Venancio, Patrícia Piacsek, Bruna Dias, André Belem, Karen Costa, Natalia Vázquez Riveiros, and Ana Luiza Albuquerque

The climate system experienced several periodic oscillations over the last ca. 800 ka known as glacial-interglacial (G-IG) cycles. Disruptions of the global carbon cycle were evident on this time scale, promoting fluctuations in the atmospheric CO2 concentration leading to global climate variability. In the more recent interglacials, both Antarctic temperatures and atmospheric CO2 concentrations are significantly higher than in the previous “lukewarm interglacials” (ca. 800 – 430 ka) before the Mid-Brunhes Transition (MBT). Changes in the Atlantic Meridional Overturning Circulation (AMOC) and deepwater formation rate around Antarctica have been invoked to explain a 30 ppm increase in the atmospheric CO2 ­during post-MBT interglacial periods. Deepwater variability is tightly coupled to the ventilation of CO2 in the Southern Ocean by atmospheric and oceanic connections, contributing to carbon storage in the deep ocean and the atmospheric CO2. Here, we present a new 770 ka benthic foraminifera δ13C record from sediment core GL-854 retrieved from the western South Atlantic (WSA) at 2200 m water depth. We compare our record with published δ13C data from the eastern margin to investigate the zonal gradient variability of the North Atlantic Deep Water (NADW) in the deep South Atlantic basin. WSA δ13C variability and absolute values strongly mimic the North Atlantic mid-depth record at the NADW formation region. This similarity is interpreted as NADW preferentially carrying a modified signal through the deep western boundary current towards the WSA (rather than towards the eastern margin) after the MBT. The δ13C gradient based on the difference between benthic foraminifera C. wuellerstorfi from both margins (Δδ13Cw-e) gradually increases after a transitional period between ca. 400 ka to 300 ka towards the Holocene. We suggest that the mechanism behind this long-term increasing trend on the Δδ13Cw-e record post-MBT is the result of enhanced production of North Component Water due to Agulhas Leakage intensification driven by reduced sea-ice extent after the MBT. Furthermore, reduced sea-ice extent decreases the Antarctic Bottom Water density and formation in the Southern Ocean, contributing to the deepening of the AMOC during post-MBT interglacial periods. Our interpretation proposes a framework connecting sea-ice and ocean-atmosphere dynamics to deepwater geometry within the South Atlantic basin, which ultimately contributed to the climate change observed across the MBT.

How to cite: Ballalai, J., Santos, T., Nascimento, R., Venancio, I., Piacsek, P., Dias, B., Belem, A., Costa, K., Vázquez Riveiros, N., and Albuquerque, A. L.: Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8018, https://doi.org/10.5194/egusphere-egu22-8018, 2022.

EGU22-13443 | Presentations | CL1.1.3

Mid-Brunhes Transition caused by Antarctic ice sheet melting during MIS11c

Xu Zhang, Stephen Barker, Martin Werner, Yuchen Sun, and Chronis Tzedakis

Interglacial intensity in past 800 kyr is characterized by a transition, about 430 kyr ago, between the older ones, which were relatively cool and low sea level, and the more recent ones, which were relatively warm and high sea level. This transition, as identified in Antarctic ice core and benthic calcite d18Oc records, corresponds to the so-called mid-Brunhes Transition (MBT). However, its origin and underlying dynamics remain elusive. Here we show, based on a start-of-art, stable water isotope enabled climate model, that additional ice volume to the present-day levels should be considered in order to reproduce the systematic enrichment in interglacial d18Oc before the MBT. This extra ice of ~18 e.s.l.m. likely exists in the Antarctic, which in turn weakens vertical mixing in Southern Ocean, potentially accounting for the low interglacial atmospheric CO2 levels prior to the MBT. Our results further indicate that during MIS11c the unique climate background leads to extra Antarctic ice sheet melting, eventually giving rise to a systematic change in interglacial climate and hence accounting for the MBT.

How to cite: Zhang, X., Barker, S., Werner, M., Sun, Y., and Tzedakis, C.: Mid-Brunhes Transition caused by Antarctic ice sheet melting during MIS11c, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13443, https://doi.org/10.5194/egusphere-egu22-13443, 2022.

EGU22-13117 | Presentations | CL1.1.3

Impacts of insolation and CO2 on the spatial differences of the MIS-9 and MIS-11 climate between monsoonal China and central Asia 

Hao Lu, Qiuzhen Yin, Zhipeng Wu, Feng Shi, Qinzhen Hao, Dunsheng Xia, and Zhengtang Guo

Marine oxygen isotope records and ice cores in Antarctica suggest that Marine Isotope Stage (MIS) 9, an interglacial occurring about 300 ka ago, is a strong interglacial and has the highest greenhouse gases (GHG) concentrations during the past 800 ka. Model results also show that MIS-9 is the warmest interglacial among the last nine ones as a result of both its high CO2 concentration and its high summer insolation in the northern Hemisphere (NH). However, the China loess records show that the paleosol S3 that corresponds to MIS-9 is not necessarily strong as compared to some other paleosol units such as the S4 soil that was formed during MIS-11, suggesting relatively drier climate condition during MIS-9. By contrast, in Tajikistan of southern central Asia, the paleosol S3 is the most developed soil over the past 800 ka, indicating a relatively warm and humid climate conditions. The difference in the paleosol formation and the MIS-9 climate between monsoonal China and central Asia is intriguing. In this study, we combine loess records from monsoonal China and central Asia as well as climate simulation results to understand the spatial difference of the MIS-9 climate in particular in comparison with the climate of MIS-11. The individual and combined contributions of insolation and greenhouse gases are quantified through simulations with the LOVECLIM model and using the factor separation technique. Our results show that the simulated effective moisture conditions between northern China and southern central Asia are consistent with the loess records and field observation. Insolation leads to much more annual mean precipitation than GHG during MIS-9 in southern central Asia, explaining a much wetter MIS-9 there. By contrast, both insolation and GHG lead to more annual mean precipitation and evaporation during MIS-9 in northern China, leading to only a slight difference in the effective moisture between MIS-9 and MIS-11. In addition, compared to MIS-11, the larger obliquity and higher GHG concentration during MIS-9 lead to an anomalous atmospheric circulation pattern similar to negative phase of North Atlantic Oscillation (NAO), favoring precipitation increase in southern central Asia and therefore explain strong soil development in Tajikistan.

How to cite: Lu, H., Yin, Q., Wu, Z., Shi, F., Hao, Q., Xia, D., and Guo, Z.: Impacts of insolation and CO2 on the spatial differences of the MIS-9 and MIS-11 climate between monsoonal China and central Asia , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13117, https://doi.org/10.5194/egusphere-egu22-13117, 2022.

EGU22-12943 | Presentations | CL1.1.3

Arctic Amplification through Inter-seasonal Feedback Effect in Past Interglacials 

Lynn Hirose, Ayako Abe-Ouchi, Masakazu Yoshimori, Wing-Le Chan, Ryouta O'ishi, and Takashi Obase

Past interglacials allow investigating the climatic processes and associated feedbacks during warm periods, which are characterized by different combinations of climatic forcing such as solar radiation, GHGs, and ice sheets. Arctic warming amplification, a common phenomenon between past interglacials and present warming, has seasonality in its feedback mechanism, and detailed study of these internal feedbacks is still lacking despite its global impact. In this study, the simulation experiments under conditions close to the past interglacial periods (MIS1; Holocene, MIS5e; Last Interglacial, and MIS11) are conducted using a coupled atmosphere-ocean-vegetation model MIROC (4m) AOVGCM, particularly focusing on the role of ice sheets and Arctic sea ice. Climate responses to inputs and conditions are compared to examine the seasonal effects of atmosphere-ocean-ice feedbacks on Northern hemisphere high-latitudes temperature. Ice sheet distribution is set as a boundary condition in addition to the orbital elements, land cover, and GHGs to account the effect of remaining ice sheets at the timing of peak insolation. Feedback Analysis is also conducted to quantify the contribution of each feedback element to the surface temperature change. It is demonstrated that an inter-seasonal effect of air-sea-ice-vegetation feedbacks contributes to Arctic warming amplification, where heat gained in summer is used for sea ice melting and ocean absorption, and is released in autumn and winter, resulting in annual warming. This process is amplified when considering vegetation feedbacks and seen commonly in MIS1, 5e, and 11. In periods when ice sheets remain, Arctic sea ice keeps a high degree of concentration in summer, and annual mean temperatures at Northern high latitudes are lower than would be expected from insolation intensity. These results imply that the presence of Northern hemisphere ice sheet has a significant effect on Arctic climate response to insolation intensity by suppressing feedbacks that contribute to Arctic amplification through the reduced melt of summer sea ice.

How to cite: Hirose, L., Abe-Ouchi, A., Yoshimori, M., Chan, W.-L., O'ishi, R., and Obase, T.: Arctic Amplification through Inter-seasonal Feedback Effect in Past Interglacials , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12943, https://doi.org/10.5194/egusphere-egu22-12943, 2022.

EGU22-3033 | Presentations | CL1.1.3

Diverse models, diverse interglacial results? Sea ice physics versus model forcing

Louise Sime, Rachel Diamond, David Schroeder, Maria Vittoria Guarino, and Rahul Sivankutty

Different IPCC-CMIP6 climate models give diverse results when run under common interglacial forcing. The mid-Holocene and the Last Interglacial are the two time periods from which we have the most results. The diversity is particularly true for the Arctic, where sea ice physics plays a key role. Whilst scientists have known for more than twenty years that summer temperatures in the Arctic during the Last Interglacial – the warm period around 127,000-128,000 years ago - were around 4°C above those of today (from lake, peat, and marine core data), the cause of this warmth puzzled scientists until 2020. Until 2020, it was thought this Last Interglacial warmth may have been driven by Arctic vegetation changes.  We present an analysis of a variety of CMIP6 model simulations run during the Last Interglacial.  Only one model simulates a fully sea ice-free Arctic during the summer –it includes an advanced representation of melt ponds in the sea ice model. Melt ponds are shallow pools of water which form on the surface of Arctic sea ice. We find that the inclusion of melt ponds within models is likely crucial for understanding Last Interglacial sea ice loss and Arctic warmth, and touch on the relationship between Arctic sea ice changes in warm climate and on high equilibrium sensitivity CMIP6 models. Alongside the impact of different physics in the models, we also consider forcing aspects including the impact of the meltwater from deglaciation and top-of-the-atmosphere radiation (orbital).

How to cite: Sime, L., Diamond, R., Schroeder, D., Guarino, M. V., and Sivankutty, R.: Diverse models, diverse interglacial results? Sea ice physics versus model forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3033, https://doi.org/10.5194/egusphere-egu22-3033, 2022.

EGU22-3087 | Presentations | CL1.1.3

Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future

Zhipeng Wu, Qiuzhen Yin, Zhengtang Guo, and André Berger

Understanding the sea ice variability and the mechanisms involved during warm periods of the Earth is essential for a better understanding of the sea ice changes at the present and in the future. Based on simulations with the model LOVECLIM, this study investigates the sea ice variations during the last nine interglacials and focuses on the inter-comparison between interglacials as well as their differences from the present and future. Our results show that, for the double CO2 experiment and the Shared Socioeconomic Pathway (SSP)1-2.6, SSP2-4.5 and SSP5-8.5 scenario experiments, the global, Arctic and Southern Ocean sea ice areas simulated by LOVECLIM all fall in the range of the multi-model results from CMIP 6. In addition, the results show that the annual mean Arctic sea ice variation is primarily controlled by local summer insolation, while the annual mean Southern Ocean sea ice variation is more influenced by the CO2 concentration but the effect of local summer insolation can’t be ignored. The lowest Arctic sea ice area results from the highest summer insolation at MIS-15, and the lowest Southern Ocean sea ice area at MIS-9 is explained by the highest CO2 concentration and moderate local summer insolation. As compared to the present, the last nine interglacials all have much less sea ice in the Arctic annually and seasonally due to high summer insolation. They also have much less Arctic sea ice in summer than the double CO2 experiment, which makes to some degree the interglacials possible analogues for the future in terms of the changes of sea ice. However, compared to the double CO2 experiment, the interglacials all have much more sea ice in the Southern Ocean due to their much lower CO2 concentration, which suggests the inappropriateness of considering the interglacials as analogues for the future in the Southern Ocean. Our results suggest that in the search for potential analogues of the present and future climate, the seasonal and regional climate variations should be considered.

Reference: Zhipeng Wu, Qiuzhen Yin, Zhengtang Guo, André Berger, 2022. Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future. Climate Dynamics, accepted.

How to cite: Wu, Z., Yin, Q., Guo, Z., and Berger, A.: Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3087, https://doi.org/10.5194/egusphere-egu22-3087, 2022.

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, is a relatively long warm period characterized by climate oscillations consisting of three interstadials and two stadials. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO2 and Northern Hemisphere ice sheets on the internal variations within MIS-5 and spatial variations of the East Asian climate, including the East Asian summer monsoon (EASM) intensity. The first set of experiments are forced by varying insolation and GHGs (OrbGHG) and the second ones are forced by varying insolation, GHGs and ice sheets (OrbGHGIce). Results show that a similar trend with precession can be found in the simulated summer precipitation, temperature and EASM index in both OrbGHG and OrbGHGIce, indicating the dominant role of precession on the EASM. Within the range of CO2 variability during MIS-5, the change of CO2 causes similar degree of warming effect, but much lower degree of humidifying effect compared to insolation. Insolation and CO2 change the precipitation through different dynamic and thermodynamic processes. Our results also show that the influence of ice sheets on temperature and precipitation is less important than the effect of insolation and it varies from regions and in time. The effect of ice sheets depends on background insolation and also the location, height and area of ice sheets. The simulated spatial-temporal variations of the EASM climate are compared with proxy records and the mechanisms involved are investigated. 

How to cite: Lyu, A. and Yin, Q.: The spatial-temporal patterns of East Asian climate in response to insolation, CO2 and ice sheets during MIS-5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2635, https://doi.org/10.5194/egusphere-egu22-2635, 2022.

EGU22-7456 | Presentations | CL1.1.3

Differences in the rates and character of the last two glacial terminations and impacts on the following interglacials

Edward Gasson and Heather Stoll

EGU22-10148 | Presentations | CL1.1.3

Higher state of the North Atlantic Oscillation during the Last Interglacial (130-115 ka BP): evidence from temperature and hydrology in the Dead Sea 

Emmanuel Guillerm, Véronique Gardien, Niels Brall, Daniel Ariztegui, Markus Schwab, Ina Neugebauer, Nicolas Waldmann, Adeline Lach, and Frédéric Caupin

The North Atlantic Oscillation (NAO) is currently the main mode of winter atmospheric variability in the extratropical Northern Hemisphere. It represents the fluctuation of the meridional sea-level pressure gradient in the North Atlantic, with high and low phases defined by high and low pressure gradients, respectively. High (or low) NAO phases are associated with wet and warm (or dry and cold) weather conditions in Northern Europe. In mid latitude regions such as the Mediterranean, this relationship is inverse, producing dry and cold (or wet and warm) conditions. Whether or not the average state of the NAO may have shifted in the past is much debated, with major implications for the understanding of past regional climate. Using a climate model, Felis et al. (2004) showed that the average state of the NAO during the Last Interglacial (130-115 ka BP) was significantly higher than during the pre-industrial period, with a high plateau from ~126 to 118 ka BP. However, proxy-based reconstructions of temperature and rainfall are needed to support this. Here, we use a new method, Brillouin spectroscopy on halite fluid inclusions, to reconstruct the evolution of temperature and hydrology in the Dead Sea, southern Levant, throughout the Last Interglacial. We find lower than modern Dead Sea temperatures and a lowering freshwater influx throughout the last interglacial. Using climate data from the recent decades, we demonstrate that the temperature of the Dead Sea hypolimnion mainly depends on winter air temperature, which is itself anti-correlated with the NAO. We also demonstrate that, during years of very high NAO, rainfall is drastically reduced in the lake catchment. In light of our analysis of modern climate data, the reconstructed cold and dry conditions in the Dead Sea area is consistent with the modelled higher NAO conditions.

How to cite: Guillerm, E., Gardien, V., Brall, N., Ariztegui, D., Schwab, M., Neugebauer, I., Waldmann, N., Lach, A., and Caupin, F.: Higher state of the North Atlantic Oscillation during the Last Interglacial (130-115 ka BP): evidence from temperature and hydrology in the Dead Sea , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10148, https://doi.org/10.5194/egusphere-egu22-10148, 2022.

EGU22-12679 | Presentations | CL1.1.3

Summer Arctic temperatures in PMIP4 Last Interglacial simulations and their link to Arctic sea ice

Rahul Sivankutty, Louise Sime, Irene Malmierca Vallet, and Agatha de Boer

Investigating climate models responses and feedbacks under warmer climates is useful in building confidence in future climate projections. Here we focus on the summer sea ice in the Arctic during the Last Interglacial period (LIG), when the Arctic was warmer than the Pre-Industrial period (PI) by around 4.5 ± 1.7 K. Given that it is difficult to ascertain the state of Arctic sea ice from marine core proxies of sea ice state, we focus instead on summer surface air temperature (SSAT) in CMIP6-PMIP4 simulations and compare these with equivalent proxy data. All 12 models we have analysed show both warmer SSAT and a reduction in summer sea ice in the LIG compared to the PI, with an average warming of +3.6K and an average 52% decrease in minimum sea ice area.

 

We find that model-observation differences in LIG SSAT are linearly related to the percentage loss of summer Arctic sea ice. However this general finding does not fit the CNRM model result, which is an outlier. This simulation captures the observed pattern of SSAT, without being close to ice-free. However peculiarities in the CNRM set-up (forcing and sea ice model tuning) means it is unclear what can be drawn from this one result. CNRM aside, models tend to yield more accurate LIG SSAT changes when they are closer to an ice-free state in summer. The models which feature sea ice losses larger than the multi-model-mean sea ice loss, tend to have the smallest model-observation SSAT errors. The results of this study provides caveated support to the argument that Arctic could have been ice-free during LIG summers. That said, a careful examination of the SSAT dataset would also be value to the LIG community, given that these results are dependent on the LIG SSAT observational dataset.

 

How to cite: Sivankutty, R., Sime, L., Malmierca Vallet, I., and de Boer, A.: Summer Arctic temperatures in PMIP4 Last Interglacial simulations and their link to Arctic sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12679, https://doi.org/10.5194/egusphere-egu22-12679, 2022.

EGU22-1312 | Presentations | CL1.1.3

The significance of Atlantic Water routing in the Nordic Seas during the present interglacial

Maciej M. Telesiński, Magdalena Łącka, Agnieszka Kujawa, and Marek Zajączkowski

The Nordic Seas are a key region for global ocean circulation, crucial in water mass exchange between the North Atlantic and the Arctic oceans, and deepwater formation. The advection of Atlantic Water (AW) to the Nordic Seas is decisive for the oceanography and climate of the region and beyond. Here, we present a set of sedimentary records, including two new cores from the western Nordic Seas to reconstruct the history of AW routing in the Nordic Seas over the Holocene. Our results show that the early Holocene (11.7 - 8 ka BP) thermal maximum, caused by an “overshoot” of overturning circulation and high insolation, was limited to the eastern Nordic Seas, while the western part remained cold due to the meltwater blocking the spreading of AW. After 8 ka BP, the retreat of the freshwater lid allowed AW to reach the central Greenland Sea, where deep convection developed. The weakening of the overturning circulation during the 8.2 ka BP event could have played an important role in this circulation shift. After 5 ka BP, the increase in sea-ice export from the Arctic strengthened deep convection, which intensified the westward AW flow. A disruption of convectional activity around 2.7 ka BP, triggered by a minimum in solar activity, caused cooling and expansion of sea ice in the Nordic Seas and might have contributed to a global climatic deterioration. The overturning circulation in the Nordic Seas did not recover to its previous state until the present. We demonstrate that the rate of AW advection into the Nordic Seas alone is not enough to understand the oceanographic evolution of this area and its influence on regional or even global ocean and climate changes. The shifts in AW routing within the Nordic Seas and the rate of deep convection are also important.

How to cite: Telesiński, M. M., Łącka, M., Kujawa, A., and Zajączkowski, M.: The significance of Atlantic Water routing in the Nordic Seas during the present interglacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1312, https://doi.org/10.5194/egusphere-egu22-1312, 2022.

CL1.1.4 – Climate response to orbital forcing

EGU22-1422 | Presentations | CL1.1.4 | Highlight | Milutin Milankovic Medal Lecture

Milankovitch Theory and Global Monsoon

Hai Cheng

  The Milankovitch Theory of orbital climate change postulates that changes in the caloric summer half-year insolation (or Northern Hemisphere summer insolation (NHSI) at ~65°N latitude) drive changes in the ice-sheets extent (i.e., global ice-volume) at Earth’s orbital periods (i.e., the sensu-stricto theory). These insolation-driven changes in turn, incite ancillary changes in other parts of the global climate systems via various forcing and feedback mechanisms (the sensu-lato hypothesis). In this theoretical framework the high-latitude glaciation processes took the center stage while the low-latitude global monsoon was essentially excluded. In the last two decades, large numbers of cave d18O records with precise radiometric chronologies have propelled speleothems to the forefront of paleoclimatology. Of particular interest are the speleothem records from North America that reveal a persistent orbital pacing of the North American climate at the precession band, which is nearly in phase with changes in the global ice-volume and atmospheric CO2 but lags June insolation at 65°N by ~5000 years, in accordance with the sensu-stricto Milankovitch theory. Contrastingly, the low-latitude tropical speleothem records manifest an orbital-scale pattern of global monsoon, which is dominated by precession cycles with a nearly anti-phased relation between the two hemispheres. Importantly, the monsoon variations track summer (July/January) insolation without significant lags at the precession band. We thus suggest that precession-induced changes in summer insolation produce distinct climate variability in the ice-sheet proximal and tropical regions predominantly via the (delayed) ice-volume/CO2 forcing/feedbacks and nearly-in-phase monsoon/CH4 responses/feedbacks.

  As for global-scale millennial events that were superimposed on orbital-scale climate variations, the essence of these events—i.e., conventional ice age terminations and other smaller events (the so-called ‘low-amplitude versions of terminations’), is virtually similar. The time-series of millennial-scale variations after removing orbital insolation signals from the speleothem monsoon record and long-term trend in the Antarctic ice core temperature (δD) record characterize the millennial climate variances of both ice age termination and low-amplitude versions of termination events. Remarkably, the millennial-scale variations show significant obliquity and precession cycles that are in-phase with North Hemisphere June insolation, implying a critical role of changes in orbital insolation in triggering the ice age terminations. These observations, in turn, provide new insights into the classic ‘100 ka problem’.

  Indeed, a more comprehensive picture of orbital theory of climate is steadily emerging with the growth of new geological proxy data, particularly the low-latitude speleothem data from the vast global monsoon regime, providing critical complements to marine and ice-core data.

How to cite: Cheng, H.: Milankovitch Theory and Global Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1422, https://doi.org/10.5194/egusphere-egu22-1422, 2022.

The mechanism of stochastic resonance (SR) in a bistable system was introduced [1] to explain the glacial-interglacial cycles in the Quaternary and is still regarded as a dynamical systems paradigm for those climate cycles. In the SR the stochastic forcing must satisfy a rather stringent condition; besides, glacial inceptions occur abruptly, as well as the glacial terminations. However, these conditions do not seem to be verified in the real climate system. Here it is shown that the alternative dynamical paradigm -that may be termed deterministic excitation (DE)- in which relaxation oscillations (ROs) are excited by the astronomical forcing in a purely deterministic framework, overcomes those limitations and may therefore provide a more plausible theoretical basis for the explanation of the glacial-interglacial variability.

In an excitable dynamical system a RO connects a basic state to an unstable excited state, which is then followed by a spontaneous, slow return to the original state. Such transition is self-sustained in a given parameter range of the autonomous system, otherwise it can be excited by an external deterministic time-dependent forcing (DE) or by noise (coherence resonance). Examples of DE in ocean dynamics are presented for the Kuroshio Extension in the North Pacific and for the Antarctic Circumpolar Current in the Southern Ocean.

A 4-dimensional nonlinear excitable spectral model of the wind-driven ocean circulation [2] is then used to briefly illustrate the main aspects of excitable climate dynamics, focusing on the occurrence of coherence resonance [3], on the DE of ROs under the action of an aperiodic forcing [4] and on the tipping points due to parameter drift [5]. Finally, a classical energy balance model is extended to obtain a minimal excitable model of the late Pleistocene ice ages [Pierini, in preparation]. The timing of the interglacials, determined by the DE caused by the variations of the Earth’s orbital eccentricity and axial tilt and precession, is found to be in significant agreement with proxy data. (Support from the IPSODES-P.N.R.A. project is acknowledged)

[1] Benzi R., Parisi G., Sutera A., Vulpiani A., 1982. Tellus 34, 10-16.

[2] Pierini S., 2011. J. Phys. Oceanogr. 41, 1585-1604.

[3] Pierini S., 2012. Phys. Rev. E 85, 027101.

[4] Pierini S., Ghil M., Chekroun M.D., 2016. J. Climate 29, 4185-4202.

[5] Pierini S., Ghil M., 2021. Sci. Rep. 11, 11126.

How to cite: Pierini, S.: On the functioning of the glacial-interglacial variability: deterministic excitation vs. stochastic resonance , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1039, https://doi.org/10.5194/egusphere-egu22-1039, 2022.

EGU22-1435 | Presentations | CL1.1.4

Towards an astrochronological tuned age model for the upper Pliocene–lower Pleistocene Western Foreland Basin of Taiwan

Romain Vaucher, Christian Zeeden, Amy Hsieh, Stefanie Kaboth-Bahr, Andrew T. Lin, Chorng-Shern Horng, and Shahin E. Dashtgard

The stratigraphic records of shallow-marine environments are not commonly regarded as excellent climate archives because of their presumed temporal incompleteness. However, a recent study of lower Pleistocene strata in the Western Foreland Basin, Taiwan, reveals high-resolution records of past climate oscillations preserved within shallow-marine strata. Deriving such narratives is made possible because of the high accommodation and sedimentation rates in the basin, which enhanced the completeness of the stratigraphic record.

Here, we astrochronologically tune the Chinshui Shale and the lower part of the Cholan Formation of the Western Foreland Basin from approximately 3.5 to 2 Ma. These strata are calibrated to global deep-sea stable oxygen isotope (δ18O) records with established time scales detailing global climate change during the studied time period. The Chinshui Shale is mudstone-dominated and was deposited mostly in offshore settings, while the Cholan Formation comprises mainly heterolithic strata deposited in shallower settings (i.e., offshore transition, nearshore) of the paleo-Taiwan Strait. The data used herein are two borehole gamma-ray profiles through the Chinshui Shale and the Cholan Formation that have a proximal-distal relation to Taiwan. High gamma-ray values reflect clay-rich intervals and correlate to lower values of δ18O in the global reference records. Low gamma-ray values point to sand-rich packages and correlate with higher values of δ18O.

Preliminary results show that the alternating clay-rich to sand-rich deposits during the late Pliocene to early Pleistocene are orbitally paced. The results allow us to i) tune the upper Pliocene–lower Pleistocene Chinshui Shale and lower part of the Cholan Formation, ii) refine the magneto-biostratigraphic framework established for this time interval in the Western Foreland Basin of Taiwan, and iii) lay the groundwork for connecting climatic changes in Taiwan during this time period to the wider frame of global climate change. 

How to cite: Vaucher, R., Zeeden, C., Hsieh, A., Kaboth-Bahr, S., Lin, A. T., Horng, C.-S., and Dashtgard, S. E.: Towards an astrochronological tuned age model for the upper Pliocene–lower Pleistocene Western Foreland Basin of Taiwan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1435, https://doi.org/10.5194/egusphere-egu22-1435, 2022.

EGU22-1451 | Presentations | CL1.1.4

Multiproxy paleoceanography from Broken Ridge pinpoints the onset of Tasman Leakage at 6.6 Ma

Jing Lyu, Beth Christensen, Gerald Auer, and David De Vleeschouwer

Inter-basinal heat and water exchange play a prominent role in driving global climate change on astronomical timescales, as part of the global thermohaline circulation. Tasman Leakage connects the Pacific and Indian Oceans at an intermediate water depth, south of Australia. Therewith, Tasman Leakage advects heat toward the Indian Ocean, and ultimately toward the Agulhas system. Hence, Tasman Leakage constitutes a non-negligible part of the present-day thermohaline circulation. The onset of Tasman Leakage likely occurred sometime in the Late Miocene (Christensen et al., 2021), but precise geochronology for the establishment of this inter-basinal connection is still lacking. Moreover, Tasman Leakage sensitivity to astronomical forcing remains to be constrained in detail. To understand Tasman Leakage on astronomical timescales, we present a new Miocene-to-recent multi-proxy dataset from Ocean Drilling Program (ODP) Sites 752 and 754, cored on Broken Ridge (30°53.475’S), southeastern Indian Ocean.

The dataset consists of new X-ray Fluorescence (XRF) core scans that provide element contents for 18 different elements, along with benthic carbon and oxygen stable isotopic records at 4 cm resolution. The XRF-derived Ca/Fe record is paced by 405-kyr eccentricity between 22 Ma and 13 Ma (early-middle Miocene), but then becomes more sensitive to obliquity and precession forcing. The new high-resolution benthic δ13C record confirms the onset of Tasman Leakage in the Late Miocene, more specifically at 6.6 Ma. This is when the Broken Ridge benthic δ13C signature no longer reflects an Antarctic Intermediate Water signal. The benthic δ18O record shows a strong ~110-kyr eccentricity imprint, indicating that Tasman Leakage might be most sensitive to this astronomical parameter. We conclude that the Neogene nannofossil oozes, preserved on Broken Ridge, constitute an excellent paleoceanographic archive that allows us to fingerprint Tasman Leakage sensitivity to astronomical forcing.

How to cite: Lyu, J., Christensen, B., Auer, G., and De Vleeschouwer, D.: Multiproxy paleoceanography from Broken Ridge pinpoints the onset of Tasman Leakage at 6.6 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1451, https://doi.org/10.5194/egusphere-egu22-1451, 2022.

EGU22-1982 | Presentations | CL1.1.4

Plio-Pleistocene Perth Basin water temperatures and Leeuwin Current dynamics (Indian Ocean) derived from oxygen and clumped isotope paleothermometry

David De Vleeschouwer, Marion Peral, Marta Marchegiano, Angelina Füllberg, Niklas Meinicke, Heiko Pälike, Gerald Auer, Benjamin Petrick, Christoph Snoeck, Steven Goderis, and Philippe Claeys

The Pliocene sedimentary record provides a window into Earth’s climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-road future climate projections. Indeed, the increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in West-Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project constructed a new orbitally-resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ18O and clumped isotopes Δ47) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. It complements an existing TEX86 record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (ODP Site 763 and IODP Site U1463). The comparison of TEX86 and Δ47 paleothermometers reveals that TEX86 likely reflects sea surface temperatures (SST, 23.8–28.9 °C), whereas T. sacculifer Δ47 calcification temperatures probably echo the state of the lower mixed layer and upper thermocline at the studied Site U1459 (18.2–20.8 °C). The isotopic δ18O gradient along a 19° S–29° S latitudinal transect, between 3.9–2.2 Ma, displays large variability, ranging between 0.5 and 2.0 ‰, whereby a low latitudinal gradient is indicative of a strong Leeuwin Current and vice versa. These results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (~0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. A period of relatively weak Leeuwin Current between 3.7 and 3.1 Ma is advocated; a time interval also marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are rooted in the same forcing: Heat transport through the Indonesian Throughflow (ITF) valve propagated to the temperate zone through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

How to cite: De Vleeschouwer, D., Peral, M., Marchegiano, M., Füllberg, A., Meinicke, N., Pälike, H., Auer, G., Petrick, B., Snoeck, C., Goderis, S., and Claeys, P.: Plio-Pleistocene Perth Basin water temperatures and Leeuwin Current dynamics (Indian Ocean) derived from oxygen and clumped isotope paleothermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1982, https://doi.org/10.5194/egusphere-egu22-1982, 2022.

EGU22-2038 | Presentations | CL1.1.4 | Highlight

Paleo-ENSO influence on African environmentsand early modern humans

Stefanie Kaboth-Bahr, William D. Gosling, Ralf Vogelsang, André Bahr, Eleanor M. L. Scerri, Asfawossen Asrat, Andrew S. Cohen, Walter Düsing, Verena Foerster, Henry F. Lamb, Mark A. Maslin, Helen M. Roberts, Frank Schäbitz, and Martin H. Trauth

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620,000 years, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of the Walker Circulation, that was most likely driven by changes in Earth’s eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle to Late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans.

How to cite: Kaboth-Bahr, S., Gosling, W. D., Vogelsang, R., Bahr, A., Scerri, E. M. L., Asrat, A., Cohen, A. S., Düsing, W., Foerster, V., Lamb, H. F., Maslin, M. A., Roberts, H. M., Schäbitz, F., and Trauth, M. H.: Paleo-ENSO influence on African environmentsand early modern humans, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2038, https://doi.org/10.5194/egusphere-egu22-2038, 2022.

EGU22-2362 | Presentations | CL1.1.4

Orbital-scale deoxygenation trends driven by ventilation in Cretaceous ocean

Anta-Clarisse Sarr, Marie Laugié, Yannick Donnadieu, Jean-Baptiste Ladant, and François Raisson

Mechanisms driving cyclicity in the marine realm during hothouse climate periods in response to Earth’s orbit variations remains debated. Orbital cycles fingerprint in the oceanographic records results from the effect of terrestrial (eg. weathering-derived nutrient supply, freshwater discharge) and oceanic (eg. productivity, oxygenation) processes, whose respective contribution remains to be defined. Here we investigate the effect of extreme orbital configurations on oxygenation state of the ocean using ocean biogeochemistry simulations with the IPSL-CM5A2 Earth System Model under (CT) Cenomanian-Turonian boundary conditions. We also use an additional inert artificial tracer allowing to compute the age of water masses, corresponding to the time spent since the last contact with the surface. Our simulations show that small ocean ventilation changes triggered by orbitally-induced variations in high latitude deep water formation have strong impact on the oceanic oxygen spatial distribution. It is particularly true for the proto-Atlantic basin which is the less oxygenated basin during the CT (Laugie et al., 2021). The eight sets of orbital parameters tested here imply changes in the Atlantic anoxic seafloor area going from 20 to 80%. All three parameters describing the Earth’s orbit (eccentricity, precession and obliquity) show a substantial control on these fluctuations. We also note that orbital fluctuations result in important changes in continental runoff but the impact remains highly localized to coastal environments – the open ocean mainly responding to the ocean ventilation. Last but not least, changes in productivity induced by the orbital parameters remain spatially heterogeneous and could be responsible for more local signal within a single basin.

 

Laugié, M., Donnadieu, Y., Ladant, J. B., Bopp, L., Ethé, C., & Raisson, F. (2021). Exploring the impact of Cenomanian paleogeography and marine gateways on oceanic oxygen. Paleoceanography and Paleoclimatology, 36(7):e2020PA004202.

How to cite: Sarr, A.-C., Laugié, M., Donnadieu, Y., Ladant, J.-B., and Raisson, F.: Orbital-scale deoxygenation trends driven by ventilation in Cretaceous ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2362, https://doi.org/10.5194/egusphere-egu22-2362, 2022.

EGU22-3744 | Presentations | CL1.1.4

Astronomical Climate Pacing in a Model Framework for Late Triassic Lake Level Cycles

Jan Landwehrs, Michael Wagreich, Georg Feulner, Matteo Willeit, Jessica H. Whiteside, and Paul E. Olsen

Combining both detailed geological records and climate modeling provides exciting opportunities to understand orbital effects on the early Mesozoic greenhouse climate across the supercontinent Pangaea. Lake sediments from the Newark-Hartford Basins (NHB) of the eastern US record cyclic climate changes in the tropics of Pangaea during the Late Triassic and earliest Jurassic (~233–199 Ma). We explore how the combined climatic effect of orbital forcing, paleogeographic changes and atmospheric pCO2 variations could have contributed to major features of this record.

For this, we assess results from an ensemble of transient, orbitally driven climate simulations for nine geologic timeslices, three atmospheric pCO2 values and two paleogeographic reconstructions. Each simulation is run with an idealized orbital forcing, with precession, modulated by eccentricity, and obliquity oscillating over a 250 kyr interval. The long duration and large number of simulations is achieved by utilizing the fast CLIMBER-X Earth System Model.

A transition from tropical humid to more seasonal and ultimately semi-arid climates is associated with the tectonic drift of the NHB region from the equator to ~20°N. The orbital modulation of the precipitation-evaporation balance that could be recorded in the lake sediments is most pronounced during 220 to 200 Ma, while it is limited by weak seasonality and increasing aridity before and afterwards, respectively. Lower pCO2 values around 205 Ma contribute to drier climates and could have led to the damping of sediment cyclicity observed at this time. Eccentricity-modulated precession dominates the orbital climate response in the NHB area, with maximum humidity associated to high spring-summer insolation and enhanced moisture import from the Tethys sea. High obliquity further amplifies summer precipitation through the seasonally shifting tropical rainfall belt.

We furthermore show how contemporaneous proxy localities, e.g. in the Germanic Basin, Junggar Basin or Colorado Plateau, can also be evaluated in this model framework. Studying the varying climate response in these different areas provides directions towards an integrated picture of global astronomical climate pacing in the Late Triassic. Furthermore, the presented approach is readily applicable to other periods in Earth history.

How to cite: Landwehrs, J., Wagreich, M., Feulner, G., Willeit, M., Whiteside, J. H., and Olsen, P. E.: Astronomical Climate Pacing in a Model Framework for Late Triassic Lake Level Cycles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3744, https://doi.org/10.5194/egusphere-egu22-3744, 2022.

EGU22-4667 | Presentations | CL1.1.4

Orbital forcing of early Eocene hyperthermal events: A new benthic foraminiferal record from the Indian Ocean, 50-51 Ma

Nicola Kirby, Sietske Batenburg, Melanie Leng, Tom Dunkley Jones, and Kirsty Edgar

The early Eocene greenhouse climate is characterised by a series of ‘hyperthermal’ events, defined by transient negative excursions in marine carbonate carbon and oxygen isotopes. Proxy records of the larger magnitude hyperthermal events are consistent with massive carbon release to the ocean-atmosphere system and associated with global warming and ocean acidification. Such events therefore represent the best analogues for current anthropogenic climate change. However, the causes and nature of smaller early Eocene hyperthermals, particularly through the early Eocene Climatic Optimum (EECO), are less well understood. We know that hyperthermal events are paced by the 100 kyr (short) and 405 kyr (long) eccentricity cycles, indicating that Earth’s orbital parameters play a key role in driving carbon cycle perturbations, but the precise forcing mechanisms remain unclear. Additionally, few continuous records of the smaller, orbitally-paced hyperthermals exist and there have been no published high-resolution climate records from the Indian Ocean so far from this interval. High-resolution records across the full spectrum of hyperthermal events and from multiple ocean basins are needed to fully identify their cause(s). Here, we constrain the nature and magnitude of environmental change during hyperthermal events O-T in the Indian Ocean using a new, high-resolution benthic stable isotope record from IODP Expedition 369 Site U1514, Indian Ocean, from 50-51 Ma. Using spectral analysis techniques, we identify the dominant periodicities in the benthic stable isotope record and investigate the phasing between stable isotopes and other environmental records from Site U1514, including sedimentary Ca/Fe. We compare the Site U1514 stable isotope record with environmental records across this time interval from other sites to determine the synchronicity of climate and carbon cycle changes between different ocean basins, aiming to further examine the forcing mechanisms of these early Eocene hyperthermal events. 

How to cite: Kirby, N., Batenburg, S., Leng, M., Dunkley Jones, T., and Edgar, K.: Orbital forcing of early Eocene hyperthermal events: A new benthic foraminiferal record from the Indian Ocean, 50-51 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4667, https://doi.org/10.5194/egusphere-egu22-4667, 2022.

EGU22-6073 | Presentations | CL1.1.4

Astronomical forcing as a trigger of abrupt climate changes at the end of interglacials 

Qiuzhen Yin, Zhipeng Wu, Andre Berger, Hugues Goosse, and David Hodell

Many paleoclimate records show that the end of interglacials of the late Pleistocene was marked by abrupt cooling events and increased millennial variability. Strong abrupt cooling occurring when climate was still in a warm interglacial condition is puzzling and its cause remains uncertain. In this study, we performed transient climate simulations for all the eleven interglacial (sub)stages of the past 800,000 years with the model LOVECLIM1.3 (Yin et al., 2021). Our results show that there exists a threshold in the astronomically induced insolation below which abrupt changes at the end of interglacials occur. When the summer insolation in the Northern Hemisphere (NH) high latitudes decreases to a critical value, it triggers a strong, abrupt weakening of the Atlantic meridional overturning circulation (AMOC) and a strong cooling in the NH followed by high-amplitude variability. The mechanism involves sea ice feedbacks in the Northern Nordic Sea and the Labrador Sea. Similar abrupt oscillations happen in the simulated temperature, precipitation and vegetation from low to high latitudes. Our simulated results are supported by observations from many marine and terrestrial records, including for example the planktic d18O record from the Iberian Margin, the Greenland ice core record and the Chinese speleothem records. Our study shows that the astronomically-induced slow variation of insolation could trigger abrupt climate changes. The insolation threshold occurred at the end of each interglacial of the past 800,000 years, suggesting its fundamental role in terminating the warm climate conditions of the interglacials. Our results show that the next insolation threshold will occur in 50,000 years, suggesting an exceptionally long interglacial ahead, which is in line with what has been suggested by previous modelling studies. 

Reference:  Yin Q.Z., Wu Z.P., Berger A., Goosse H., Hodell D., 2021. Insolation triggered abrupt weakening of Atlantic circulation at the end of interglacials. Science, 373, 1035-1040, DOI: 10.1126/science.abg1737

How to cite: Yin, Q., Wu, Z., Berger, A., Goosse, H., and Hodell, D.: Astronomical forcing as a trigger of abrupt climate changes at the end of interglacials , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6073, https://doi.org/10.5194/egusphere-egu22-6073, 2022.

EGU22-5323 | Presentations | CL1.1.4 | Highlight

The Resonant Tidal Evolution of the Earth-Moon Distance

Mohammad Farhat, Pierre Auclair-Desrotour, Gwenaël Boué, and Jacques Laskar

Due to tidal interactions in the Earth-Moon system, the spin of the Earth slows down with time and the Moon drifts away. This present recession of the Moon is now measured with great precision using Lunar Laser Ranging, but it has been realised, more than fifty years ago, that simple solid-Earth tidal models extrapolated backwards in time lead to an age of the Moon that is by far incompatible with the geochronological and geochemical evidence. Since then, in order to evade this paradox, more elaborated models have been proposed, taking into account the tidal frequency-dependent oceanic dissipation; but none so far has been able to fit both the estimated lunar age and the present rate of lunar recession. In this talk, we present a physical model that reconciles these two constraints and yields a unique solution of the tidal history. This solution fits remarkably well the available geological proxies and consolidates the cyclostratigraphic method, although such a fit was not imposed. The resulting evolution involves multiple crossings of resonances in the oceanic dissipation that are associated with significant and rapid variations in the lunar orbital distance, the Earth’s length of the day, obliquity, and precession frequency. 

How to cite: Farhat, M., Auclair-Desrotour, P., Boué, G., and Laskar, J.: The Resonant Tidal Evolution of the Earth-Moon Distance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5323, https://doi.org/10.5194/egusphere-egu22-5323, 2022.

EGU22-6423 | Presentations | CL1.1.4

Integrating astronomical solutions and geological observations

Matthias Sinnesael and Jacques Laskar

Some of the large climatic changes of the past originate in the variations of the Earth’s orbit and of its spin axis resulting from the gravitational pull of the planets and the Moon. These variations can be traced over several millions of years back in time (Ma) in the geological sedimentary records (e.g. Milankovitch cycles). Over the last decades, the Earth’s orbital and spin solutions have been used to establish a geological timescale based on the astronomical solutions. Nevertheless, extending this procedure through the Mesozoic Era (66-252 Ma) and beyond is difficult, as the solar system motion is chaotic. It will thus not be possible to retrieve the precise orbital motion of the planets beyond 60 Ma from their present state.

Astrogeo, a project funded by the European Research Council (ERC), will use the geological record as an input to break the horizon of predictability of 60 Ma resulting from the chaotic motion of the planets. This will be achieved by considering statistical methods and by using ancient geological data as an additional constraint in obtaining astronomical solutions. Astrogeo aims to provide a template orbital solution for the Earth that could be used for paleoclimate studies over any geological time. This will open a new era where the geological records will be used to retrieve the orbital evolution of the solar system. It will thus open a new observational window for retrieving not only the history of the Earth, but of the entire solar system. Here, we want to reach out to the broader cyclostratigraphic community to discuss suitable procedures and data sets to couple both theoretical solutions and geological observations. In particular, we are interested in examining high-quality data sets with clear and well-constrained (single or combined) expressions of the astronomical parameters of eccentricity, precession and obliquity.

How to cite: Sinnesael, M. and Laskar, J.: Integrating astronomical solutions and geological observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6423, https://doi.org/10.5194/egusphere-egu22-6423, 2022.

EGU22-6429 | Presentations | CL1.1.4

Perturbations of volcanic CO2 emission to orbital paced climate-carbon cycle

Fenghao Liu, Enqing Huang, Jinlong Du, Wentao Ma, Xiaolin Ma, Lucas Lourens, and Jun Tian

How the global carbon cycle and climate changes interact on orbital timescales under different boundary conditions remains elusive. Previous studies have found that changes in global ice-sheet volume and marine carbon cycle are synchronized at the eccentricity time scales with a slight lead of climate-cryosphere relative to carbon cycle throughout Oligo-Miocene (~34-6 Ma). Here, we analyze the evolutive phase relationship between benthic foraminiferal oxygen (δ18O) and carbon isotope (δ13C) to reveal an unnoticed phenomenon that variations of oceanic carbon cycle could lead those of global ice-sheet volume on 405-kyr cycle during Miocene Climate Optimum (MCO, ~17-14 Ma), which was a profound warming interval partly ascribed to the carbon emission from the eruption of the Columbia River Basalts Group (CRBG). Eccentricity sensitivity analysis indicate a relatively constant response of ice sheet to orbital forcing during MCO. Combined the results of box model, we propose that volcanic CO2 input accelerates the response of marine carbon cycle to orbital forcing. The enhanced greenhouses effect probably had strengthened the low-latitude hydrological cycle and chemical weathering and ultimately generated the δ13C-lead-δ18O scenario.

How to cite: Liu, F., Huang, E., Du, J., Ma, W., Ma, X., Lourens, L., and Tian, J.: Perturbations of volcanic CO2 emission to orbital paced climate-carbon cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6429, https://doi.org/10.5194/egusphere-egu22-6429, 2022.

EGU22-6783 | Presentations | CL1.1.4

Cyclostratigraphy of the Aptian-Albian transition in southern Tunisia (Southern Tethys): sequence stratigraphy and geochronologic implications

Hamdi Omar, Anne-Christine Da Silva, and Chokri Yaich

EGU22-11342 | Presentations | CL1.1.4

Astronomical modulation of oxygenation conditions during the Telychian (Silurian) recorded in the Sommerodde-1 core from Bornholm Denmark.

Michiel Arts, David De Vleeschouwer, Niels H. Schovsbo, Nicolas Thibault, Arnie T. Nielsen, and Anne-Christine Da Silva

The Silurian (443.8-419.2 million years ago) is a period of important biodiversity changes, dynamic climate change, including strong sea level fluctuations and the development of low-oxygen conditions in the ocean1-2-3. To date the Silurian lacks in (cyclostratigraphic) age constraints and in understanding in the way astronomical cycles modulate the Silurian climate, which hinders our understanding of Silurian climate dynamics. To assess the role of astronomical cycles in the pacing of the Silurian climate, we study the imprint of astronomical cycles on the record of the Sommerode-1 core from Bornholm, Denmark (53.65-118.66m).The core contains a near continuous Telychian record including the SOCIE and Valgu carbon isotope excursions/events4-5-6.  The core was scanned at University of Bremen/ MARUM (November 2021) using the Bruker M4 Tornado µXRF scanner, enabling for a high-resolution cyclostratigraphic and chemostratigraphic study of the Telychian.

XRF core measurements provided semi-quantitative element data, spaced at 0.5 mm, were converted into element concentrations (ppm) using a set of reference standards. A Principal Component Analysis simplified the variability in our dataset into 3 components. PC1 has high loadings for Al, Si, K, Ti, Fe and Co, and is interpreted as a detrital component. PC2 has high loadings for Ca and Mn, and is interpreted as an indicator of oxygenation conditions. PC3 has high loadings for S, indicative for the sulphides/dysoxic/anoxic conditions-8-9.

Peaks for Mn at 69-85m and S at 85-104m, indicate that part of the core (69-85 m) was deposited under oxic conditions while another part of the core (85-104 m) was deposited under anoxic/dysoxic conditions. We note that the transition to oxic conditions at 90 m coincides with the Valgu isotopic event4 while the SOCIE4 (80-70 m) event occurs during oxic conditions. Spectral analysis (wavelet, MTM and Evolutive Harmonic Analysis (EHA)) on the 3 components reveals the imprints of long and short eccentricity, obliquity and precession. An EHA spectra of the detrital component was used to trace the long eccentricity in the depth domain which was used to infer changes in sedimentation rates. The sedimentation rates are used to convert the record from the depth to time domain. Astronomical cycles filtered from the record in the time domain show that astronomical cycles exert a great control on the depositional record.  Indicating the astronomical cycles modulated the Telychian climate which in term paced oxygenation conditions at the sea-floor.

1.Melchin et al. (2005) The Silurian Period 525–558 –

2. Bond & Grasby (2017) Palaeogeogr., Palaeoclim., Palaeoecol. 478, 3–29. –

3. Saltzman (2005) Geology, 33, 7, 573-576. –

4. Hammarlund et al. (2019) Palaeogeogr., Palaeoclim., Palaeoecol. 526, 126–135. –

5. Schovsbo, et al. (2015). Geological Survey of Denmark and Greenland Bulletin, 33, 9–12.

6. Loydell, D. K., et al. (2017). Bulletin of the Geological Society of Denmark, 65, 135–160.

7. Algeo, T. J., & Maynard, J. B. (2004). Chemical Geology, 206(3–4), 289–318.

8. Ferriday, T., & Montenari, M. (2016). Stratigraphy & Timescales (Vol. 1).

9. Rothwell, R. G., & Croudace, I. W. (2015). Tracking Environmental Change Using Lake Sediments. (Vol. 2)

How to cite: Arts, M., De Vleeschouwer, D., Schovsbo, N. H., Thibault, N., Nielsen, A. T., and Da Silva, A.-C.: Astronomical modulation of oxygenation conditions during the Telychian (Silurian) recorded in the Sommerodde-1 core from Bornholm Denmark., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11342, https://doi.org/10.5194/egusphere-egu22-11342, 2022.

EGU22-12044 | Presentations | CL1.1.4

A new conceptual model to explain the mid-Pleistocene transition

Etienne Legrain, Frédéric Parrenin, and Emilie Capron

Pleistocene climate is primarily driven by changes of the Earth’s orbital parameters. However, the Mid-Pleistocene Transition (MPT) (~0.8-1.2Myr) which corresponds to a gradual change of interglacial-glacial cyclicity from weak 40kyr climatic cycles to the current strong 100kyr cycles, remains largely unexplained. So far, models only based on orbital forcing were not capable to reproduce this transition, discarding the hypothesis of an orbitally-driven transition. Internal Earth system climate causes were thus explored as primary drivers of the MPT, as a gradual decrease in atmospheric CO2 concentrations or the removal of the regolith beneath the northern hemisphere ice sheets. 
Here we present an improved version of the conceptual model of Parrenin and Paillard (2012) modelling ice volume variations over the past 2Myr. Our model switches between two states, a glaciation state and a deglaciation one, following a threshold mechanism related to the input parameters and the modelled ice volume itself. The modelled ice volume is compared to the ice volume reconstructions inferred from paleodata. 
 We reproduced the MPT using three different models. The “orbital” model which only use orbital forcing parameters as input. The “gradual” model, which is similar to the orbital model plus a continuous drop of a physical parameter in addition to orbital forcing parameters. The “abrupt” model, also similar to the orbital model plus a time-determined abrupt variation of a physical parameter in addition to orbital forcing parameters. 
For the first time, our conceptual model is able to simulate qualitatively the Mid-Pleistocene Transition with only changes in the orbital forcing parameters, reproducing the change in frequency and amplitude of the transition. Moreover, the hypothesis of a coupled influence of orbital forcing and a decreasing deglaciation threshold parameter is by far a better hypothesis than considering an abrupt change regarding our model results. In fact, the “gradual” model contains less parameters and a smaller data-model standard deviation of residuals than the “abrupt” model. Orbital forcing could thus have enabled the Mid-Pleistocene Transition. A combined influence with a decreasing parameter, such atmospheric  CO2 concentration, would have triggered this transition.

References 
Parrenin, F., & Paillard, D. (2012). Terminations VI and VIII (∼ 530 and∼ 720 kyr BP) tell us the importance of obliquity and precession in the triggering of deglaciations. Climate of the Past, 8(6), 2031-2037.

How to cite: Legrain, E., Parrenin, F., and Capron, E.: A new conceptual model to explain the mid-Pleistocene transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12044, https://doi.org/10.5194/egusphere-egu22-12044, 2022.

CL1.2.1 – Integrating stratigraphy, sedimentology, paleoclimate and human evolution in- and out of Africa

EGU22-2707 | Presentations | CL1.2.1

Simulating climate effects on archaic human habitats and species successions

Axel Timmermann, Kyungsook Yun, Pasquale Raia, Christoph Zollikofer, Marcia Ponce de Leon, Matteo Willeit, Andrey Ganopolski, Elke Zeller, Jiaoyang Ruan, and Elke Zeller

It has previously been suggested that climate shifts during the last 2 million years played an important role in the evolution of our genus Homo. However, quantifying this linkage has remained challenging. Here we use an unprecedented transient Pleistocene Coupled General Circulation model simulation in combination with an extensive compilation of fossil and archaeological records, to study the spatio-temporal habitat suitability of five hominin species over the past 2 million years. We show that astronomically-forced changes in temperature, rainfall and terrestrial net primary production had a major impact on their observed distributions. During the early Pleistocene hominins primarily settled in environments with weak orbital-scale climate variability. This behaviour changed drastically after the mid-Pleistocene-transition when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients, which increased  the likelihood for habitat overlap and cladogenic transitions. Our robust numerical simulations of climate-induced habitat changes provide a novel framework to test hypotheses on our human origin.

How to cite: Timmermann, A., Yun, K., Raia, P., Zollikofer, C., Ponce de Leon, M., Willeit, M., Ganopolski, A., Zeller, E., Ruan, J., and Zeller, E.: Simulating climate effects on archaic human habitats and species successions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2707, https://doi.org/10.5194/egusphere-egu22-2707, 2022.

EGU22-6682 | Presentations | CL1.2.1

Simulating Pleistocene climate effect on archaic human interbreeding

Jiaoyang Ruan, Axel Timmermann, Kyung-Sook Yun, Elke Zeller, and Danielle Lemmon

Genomic data document multiple episodes of interbreeding among Neanderthals, Denisovans and Homo sapiens. When, where and how often the interbreeding between these hominin populations took place remains unclear. Here, we study the Neanderthal-Denisovan admixture during the past 400 thousand years using a novel habitat model that integrates extensive fossil, archeological, and genetic data with unprecedented transient Coupled General Circulation Model simulations of global climate and vegetation. Our Pleistocene hindcast of habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric CO2 and northern hemisphere ice-sheet volume. Therefore glacial/interglacial climate swings likely played an important role in archaic human gene flow and genetic diversification.

How to cite: Ruan, J., Timmermann, A., Yun, K.-S., Zeller, E., and Lemmon, D.: Simulating Pleistocene climate effect on archaic human interbreeding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6682, https://doi.org/10.5194/egusphere-egu22-6682, 2022.

EGU22-6824 | Presentations | CL1.2.1

Early hominins were variability avoiders and diversity seekers

Elke Zeller, Axel Timmermann, Kyung-Soon Yun, and Pasqual Raia

Climate influenced the evolution of hominins, though the mechanisms and scales are still not well understood. We know that long-term climatic variations, such as wet-dry climate cycles and sea-level change, can change landscapes dramatically. Changes in landscapes can drive early hominins to find different locations to settle, but what kind of environments did they prefer and what role did changing climates play in all this? To research this question, we modeled the climate of the past 3 million years using CESM, made a best estimate of the global biome landscape, and compared the results to an extensive archeological database of hominin findings.

This analysis shows us that early hominins living in Africa predominantly lived in open habitats. When hominins expanded northwards, they adapted to more forested landscapes. While they were able to adapt, most hominin locations were found in areas with less variability and higher local biome diversity, suggesting that hominins prefer stable environmental conditions with a variety of resources nearby. This preference for stability and a landscape that offers diverse biomes is seen for all hominins regardless of species.

How to cite: Zeller, E., Timmermann, A., Yun, K.-S., and Raia, P.: Early hominins were variability avoiders and diversity seekers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6824, https://doi.org/10.5194/egusphere-egu22-6824, 2022.

EGU22-11141 | Presentations | CL1.2.1

Stochastic Resonance between Climate Variability and Hominin Migration in an Agent-Based Model

Danielle Lemmon, Axel Timmermann, Elke Zeller, Jiaoyang Ruan, Kyungsook Yun, and Pasquale Raia

There are many interdisciplinary theories as to how climate variability impacted hominin migration, and subsequently human evolution. One such hypothesis concerns so-called “green corridors,” in which climate and biome variability periodically opened vegetated corridors between habitable areas. The periodic opening of these corridors may have acted as a pump through uninhabitable barrier regions, allowing for more wide-spread dispersal. We present results from a climate-forced agent-based model that furthers the green corridor hypothesis to include the effect of stochastic resonance in penetrating barrier regions. In other words, while it intuitively makes sense that hominins would explore and disperse as green corridors opened up, the potential for green corridors to act as a dispersal pump likely depended on having the right amount of stochasticity (randomness) in hominin movement to resonate with orbitally-paced climate signals, effectively penetrating these corridors and dispersing into other regions. We integrate data from a 2-million-year CESM model, from the BIOME4 vegetation model, and from archaeological archives to create a map of habitat suitability based on a species-specific climate envelope. This habitat suitability forces the agent-based hominin migration model, in which agents seek more habitable areas and the added randomness in that agent movement is varied. While our conclusions are largely independent of species, we show results from a Homo erectus migration simulation. In my presentation I will discuss how stochastic hominin movement, the opening up of green corridors, and climate variability affected hominin dispersal throughout the Plio-Pleistocene.

How to cite: Lemmon, D., Timmermann, A., Zeller, E., Ruan, J., Yun, K., and Raia, P.: Stochastic Resonance between Climate Variability and Hominin Migration in an Agent-Based Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11141, https://doi.org/10.5194/egusphere-egu22-11141, 2022.

EGU22-7177 | Presentations | CL1.2.1

Early Pleistocene route to Sangiran opened to Javanese Homo erectus

Laurent Husson, Anne-Elisabeth Lebatard, Swann Zerathe, Régis Braucher, Sofwan Noerwidi, Sonny Aribowo, Julien Carcaillet, Danny Hilman Natawidjaja, Didier L. Bourlès, and Aster Team

The chronology of the arrival of Homo erectus on the island of Java is a cornerstone of paleoanthropology. Understanding the dispersal routes of Homo erectus, but also of other hominin lineages in Asia and across Southeast Asia, depends on this timing. Their dispersal across Sundaland, in particular, is challenged by an extremely transient climatic and geological environment during Early Pleistocene. Furthermore, ages of first appearance of Javanese H. erectus remain controversial. New age constraints based on cosmogenic nuclides 10Be and 26Al produced in situ indicate that H. erectus reached Java and dwelled at Sangiran at least ~1.4 Ma ago and more probably around 1.8 Ma. During this period, Java was just emerging from the sea while the adjacent Sundaland was a vast and continuous expanse of climatically and environmentally hospitable land connecting Java to mainland Asia, which facilitated the prior dispersal of hominins and terrestrial faunas to the edge of Java. This ancient age makes H. erectus the contemporary of the earliest members of the genus Homo in Africa and Asia, and rejuvenates the question of dispersal and evolutionary pathways across Eurasia and Sundaland.

How to cite: Husson, L., Lebatard, A.-E., Zerathe, S., Braucher, R., Noerwidi, S., Aribowo, S., Carcaillet, J., Natawidjaja, D. H., Bourlès, D. L., and Team, A.: Early Pleistocene route to Sangiran opened to Javanese Homo erectus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7177, https://doi.org/10.5194/egusphere-egu22-7177, 2022.

EGU22-7421 | Presentations | CL1.2.1

Developing a chronological and environmental framework of Early Pleistocene hominin expansions in the Caucasus region: Current research in northern Armenia

Jenni E Sherriff, Daniel S Adler, Dmitri Arakelyan, Boris Gasparyan, Tobias Lauer, Katie J Preece, Mark J Sier, and Keith N Wilkinson

Understanding the chronology and environmental context of the earliest hominin expansions into Eurasia is of considerable interest in palaeoanthropology, however, our current knowledge is based on a handful of sites.  Dated to 1.85–1.78 Ma, Dmanisi (southern Georgia) is not only the locus of the earliest Homo fossils in Eurasia but has also yielded stone tools and rich assemblages of vertebrate fossils (1,2).  Whilst Dmanisi fundamentally changed our views on the timing of hominin expansions out of Africa and the technological capabilities of these populations, it has long represented a single site in the region, and little is known about the broader environmental context.

The Debed Valley (located in the Lori Depression, northern Armenia) represents a key area in which to improve our understanding of this early hominin expansion. The area lies at the southeast margins of the Javakheti Plateau, a large volcanic province spanning both southern Georgia and northern Armenia. Current chronological study of the Javakheti-derived lavas places the interval of volcanic activity between 2.1 and 1.6 Ma (3,4). The lavas are exposed along the Debed valley and trap sediment sequences below, within, and atop the flows. 

Here, we present the first results of our ongoing paleoenvironmental and geoarchaeological investigations in the Debed valley. We first present a model of landscape evolution during the Early Pleistocene based on detailed geologic and geomorphic mapping in the valley. We then describe preliminary results from two of the key sequences in the valley: 1) the open-air archaeological site of Haghtanak-3, from which a Mode 1 lithic assemblage has been recovered, and 2) the fluvio-lacustrine sequence of Dzoragyugh-1 paleolake.  We discuss the stratigraphic, sedimentological, and chronological (40Ar/39Ar and palaeomagnetism) results from each site and provide linkages between these sites, the geomorphic evolution of the Debed valley, and Dmanisi sequence. Through this, we highlight the environmental and archaeological significance of sedimentary archives in northern Armenia for understanding the nature and environmental context of early hominin expansions into Eurasia.  

1) Ferring, R., Oms, O., Agustí, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D. and Lordkipanidze, D., 2011. Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85–1.78 Ma. Proceedings of the National Academy of Sciences, 108, 10432-10436.

2) Mgeladze, A., Lordkipanidze, D., Moncel, M.-H., Despriee, J., Chagelishvili, R., Nioradze, M., Nioradze, G., (2011). Hominin occupations at the Dmanisi site, Georgia, Southern Caucasus: raw materials and technical behaviours of Europe's first hominins. Journal of Human Evolution 60, 571–596.

3) Lebedev, V.A., Bubnov, S.N., Chernyshev, I.V., Chugaev, A.V., Dudauri, O.Z. and Vashakidze, G.T. (2007). Geochronology and genesis of subalkaline basaltic lava rivers at the Dzhavakheti Highland, Lesser Caucasus: K/Ar and Sr-Nd isotopic data. Geochemistry International 45, 211–225.

4) Trifonov, V.G., Lyubin, V.P., Belyaeva, E.V., Lebedev, V.A., Trikhunkov, Ya.I., Tesakov, A.S., Simakova, A.N., Veselovsky, R.V., Latyshev, A.V., Presnyakov, S.L., Isanova, T.P., Ozhereliev, D.V., Bachmanov, D.M. and Lyapunov, S.M. (2016). Stratigraphic and tectonic settings of Early Paleolithic of North-West Armenia. Quaternary International 420, 178– 198.

How to cite: Sherriff, J. E., Adler, D. S., Arakelyan, D., Gasparyan, B., Lauer, T., Preece, K. J., Sier, M. J., and Wilkinson, K. N.: Developing a chronological and environmental framework of Early Pleistocene hominin expansions in the Caucasus region: Current research in northern Armenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7421, https://doi.org/10.5194/egusphere-egu22-7421, 2022.

EGU22-1100 | Presentations | CL1.2.1

Paleoenvironmental reconstruction in East Africa at a critical period of hominin dispersion out-of-Africa (150-80 kyr)

Cecile A. Porchier, Mark A. Maslin, Tom Hill, David M. Williams, Eileen Cox, Anson W. Mackay, George E.A. Swann, and Melanie J. Leng

Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d18Odiatom) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d18Odiatomrecords are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d18Odiatom has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.

How to cite: Porchier, C. A., Maslin, M. A., Hill, T., Williams, D. M., Cox, E., Mackay, A. W., Swann, G. E. A., and Leng, M. J.: Paleoenvironmental reconstruction in East Africa at a critical period of hominin dispersion out-of-Africa (150-80 kyr), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1100, https://doi.org/10.5194/egusphere-egu22-1100, 2022.

EGU22-12497 | Presentations | CL1.2.1

Integrated approaches to locating Pleistocene archaeological and proxy sites in drylands

Paul Breeze, Nick Drake, Katie Manning, and Michael Petraglia

Surveying at the landscape scale to find archaeological sites is a particular challenge in the dryland environments of Arabia, the Sahara and other similar hyper-arid regions. Here we present how novel high-resolution palaeoydrological mapping of the entirety of the Saharo-Arabian desert belt has not only revealed large numbers of palaeolakes, shorelines and past drainage courses, but also proved particularly fruitful for finding new palaeolithic sites, and lacustrine pleistocene proxy records in Arabia. We describe the integrated survey methodologies which have helped us to locate large numbers of new sites in Arabia, including the earliest fossil and footprints of our species in Arabia, thus helping to enhance our understanding of pleistocene climatic change in these deserts, and of Hominin dispersals into and through them.

How to cite: Breeze, P., Drake, N., Manning, K., and Petraglia, M.: Integrated approaches to locating Pleistocene archaeological and proxy sites in drylands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12497, https://doi.org/10.5194/egusphere-egu22-12497, 2022.

EGU22-6559 | Presentations | CL1.2.1

Integrative multivariate study of past African climate variability

Norbert Marwan, Jonathan F. Donges, Reik V. Donner, and Deniz Eroglu

Based on a set of various marine palaeoclimate proxy records, we investigate African climate variations during the past 5 million years. We use a collection of modern approaches from non-linear time series analysis to identify and characterise dynamical regime shifts as changes in signal predictability, regularity, complexity, and higher-order stochastic properties such as multi-stability. We observe notable nonlinear transitions and important climate events in the African palaeoclimate, which can be attributed to phases of intensified Walker circulation, marine isotope stage M2, the onset of northern hemisphere glaciation, and the mid-Pleistocene transition, and relate them to variations of the Earth's orbital parameters.

How to cite: Marwan, N., Donges, J. F., Donner, R. V., and Eroglu, D.: Integrative multivariate study of past African climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6559, https://doi.org/10.5194/egusphere-egu22-6559, 2022.

EGU22-9664 | Presentations | CL1.2.1

Homo heterogenus: Variability in Pleistocene Homo environments.

Tegan Foister, Miikka Tallavaara, Mikael Fortelius, and Oscar E. Wilson

The Early Pleistocene dispersal of Homo out of Africa  is a highly studied and debated topic.  One of the controversies centres on the question of what type of environments hominin species expanded out of Africa into. We conducted a literature review of 163 papers published since 2000 studying the environmental settings of the first Out of Africa expansion. We found that the literature is polarised between two types of hypotheses. On one hand there are papers which describe Homo in the Early Pleistocene as inflexible (compared to Homo sapiens) and incapable of persisting in non-savannah environments, e.g. the ‘savannahstan’ hypothesis. On the other hand there are papers which describe Homo as flexible and able to persist in various environment types, e.g. the variability selection hypothesis. By investigating these hypotheses we are able to move closer to answering the question - as Homo dispersed out of Africa, did they diversify to exploit new environments, or remain within the ranges of their African niche? We analysed the reconstructions of early Homo environments included in these papers. We found that the qualitative language used to describe hominin environments is problematic and impedes the formation of clear conclusions about the environments occupied by early Homo species. However, by forcibly quantifying the descriptions used in 69 (of the original 163) papers we found that the research does not strongly support the savannahstan hypothesis. Instead the environments inhabited by Homo are consistently reconstructed as a mix of environment types (grassland, forest, savannah etc.), with a slight skew towards open habitats. Based on these results, we tentatively suggest that Homo exhibited a preference for heterogeneous “edge” environments during the Pleistocene and as they dispersed out of Africa. However,  in order to further investigate the potential preference of Homo for heterogeneous environments and to build confidence in reconstructions of early human environments in general, quantified reconstructions of the vegetation composition and distribution at early Homo sites are needed. 

How to cite: Foister, T., Tallavaara, M., Fortelius, M., and Wilson, O. E.: Homo heterogenus: Variability in Pleistocene Homo environments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9664, https://doi.org/10.5194/egusphere-egu22-9664, 2022.

EGU22-667 | Presentations | CL1.2.1

The Great Lakes of Turkana – a Novel Perspective on the African Humid Period

Markus Lothar Fischer and Annett Junginger

The Lake Turkana region in northern Kenya and southern Ethiopia is famous for its fossil richness including key sites for human evolution studies. Modern Lake Turkana is the last of numerous mega-paleo-lakes, that has persisted to dry up completely at the end of the last African Humid Period (AHP, 15 – 5 ka). The adjacent paleo-lakes Suguta (2,000 km²) and Chew Bahir (2,500 km²), which are desiccated today, have formed together with paleo-lake Turkana (20,000 km²) a N-S oriented mega-lake during the AHP that has being separated only by small morphological Barriers. While Turkana, Suguta and Chew Bahir have been part of intensive research during the past decades, paleo-lake Chalbi with 10,000 km² in size just 10 km east of Lake Turkana was out of sight for most archaeologists and geoscientist. Here we present the first attempts for enhancing our understanding of the paleoenvironmental consequences of paleo-lake Chalbi close to one of the key regions in human evolution.

How to cite: Fischer, M. L. and Junginger, A.: The Great Lakes of Turkana – a Novel Perspective on the African Humid Period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-667, https://doi.org/10.5194/egusphere-egu22-667, 2022.

EGU22-10334 | Presentations | CL1.2.1

The paleoenvironmental history of the wetland Gelba in the Gamo Highlands of Ethiopia: a Holocene vegetation reconstruction with sedimentary ancient DNA

Femke Augustijns, Charline Giguet-Covex, Alemayehu Kasaye Tilahun, Nils Broothaerts, and Gert Verstraeten

Multiproxy paleoenvironmental research in Ethiopia is limited to a handful of studies, mostly situated in central and northern Ethiopia. This results in lasting uncertainties about the nature and timing of the vegetation response to climatic changes such as the African Humid Period and the Holocene aridification, and the imprint of human activities on the vegetation.

Here we present the sedimentary ancient DNA (sedaDNA) and XRF results as part of a multiproxy study in the Gamo Highlands in the southern Ethiopian rift valley. A six meter long sediment core spanning the last 18 thousand years was retrieved from a wetland at Gelba at 2300 m asl in the Gamo Highlands. Previous pollen and charcoal analyses on the core showed a past vegetation dominated by Afromontane forest taxa over the entire record. A first shift in the pollen-based reconstructed vegetation was a decrease of afroalpine vegetation around 13 cal. ka BP, with a relative increase of Afromontane forest taxa. Around 7 cal. ka BP wooded grassland taxa increased. At ca. 2.5 cal. ka BP a sudden change in the vegetation was detected, with increased disturbance indicators and charcoal particles.

Samples spanning the entire core we analyzed for their plant DNA content targeting the extracellular DNA. For the last 2.5 cal. ka BP, both extracellular and total DNA extraction was applied to the investigated samples. The results showed similar results for both approaches, whilst them also being complimentary by each detecting additional taxa. The majority of DNA sequences was derived from herbs and wetland plants, indicating a relatively local vegetation signal. A first observable change in the DNA record occurs at 7 cal. ka BP (with e.g. decreasing Convolvulaceae), but the strongest shift is observed in the period 2.5-2 cal. ka BP, with in particular an increase of Lythraceae and Polygonoideae. The DNA analysis has some taxa in common with the pollen analysis, but both proxies complement each other strongly due to the dominant local versus regional signal they provide. Despite the difference in detected plant taxa, the timing of vegetation transitions matches well between both records.

The XRF results show a highly minerogenic sediment input in the late glacial period. From ca. 13 cal. ka BP, a strong decrease in minerogenic input is observed and the sediment becomes more organic. At ca. 7.5 cal. ka BP, the minerogenic input increases again until 3 cal. ka BP, followed by fluctuating levels of minerogenic elements and increasing phosphorus levels in the last 2000 years.

How to cite: Augustijns, F., Giguet-Covex, C., Tilahun, A. K., Broothaerts, N., and Verstraeten, G.: The paleoenvironmental history of the wetland Gelba in the Gamo Highlands of Ethiopia: a Holocene vegetation reconstruction with sedimentary ancient DNA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10334, https://doi.org/10.5194/egusphere-egu22-10334, 2022.

EGU22-7105 | Presentations | CL1.2.1

New sedimentological evidence of Lake Victoria’s palaeohydrological variability during the last deglacial transition (16-10 kyr BP)

Giulia Wienhues, Yunuén Temoltzin-Loranca, Hendrik Vogel, and Martin Grosjean

The East African (hydro-)climate response to perturbations during the deglacial transition (e.g. Older and Younger Dryas) is complex and expressed heterogeneously in different paleoclimatic records. Lake Victoria (LV), Africa’s largest lake, desiccated entirely during the dry last glacial (>16.3 kyr BP) and subsequently refilled as climate conditions got more humid, reaching a highstand during the Early Holocene. However, existing sediment records from LV do not have sufficient resolution to fully resolve short-term hydroclimate changes during the deglacial transition (especially between 14 and 11 kyr BP). There is little direct evidence of late-glacial lake level fluctuations in LV so far because intermediate water depth coring sites suitable to record intermittent lowstands are missing.

By analysing sediment cores along a near-shore/shallow water (current water depth 22 m) to offshore/deep water (current water depth 63 m) coring transect covering the past 16,000 years, we aim at a more accurate spatial and temporal reconstruction of LV’s deglacial lake level history in response to regional hydroclimate changes.

Core stratigraphy and geochemical evidence, combined with a robust radiocarbon chronology, demonstrate a stepwise infilling of the Lake Victoria basin after its last complete desiccation (< 16.3 kyr BP). Following the dry late glacial Heinrich 1 event, an intermediate water level prevailed between 16.3 and 14.4 kyr BP, with uninterrupted deposition of fine-grained, organic matter-rich pelagic muds at our deep-water site and coarser, sandy-clay deposits at the near shore site. A second dry episode during the Older Dryas (~14 kyr BP) is marked by an abrupt decline in lake level with deposition of coarse mollusc shell bearing sediments at the near shore site indicating a littoral depositional environment. This shift in hydroclimate in the Lake Victoria basin is congruent with a brief period of cooling and drying during the Bölling/Alleröd (Dansgard Oeschger Event 1), which is also recorded in other East African Lakes. Subsequently, Lake Victoria reached maximum water levels with the onset of the African Humid Period in the early Holocene at around 11 kyr BP, which is expressed by elevated input of chemically weathered material (e.g. Rb/K) and deposition of fine-grained muds at both the near shore and offshore sites.

How to cite: Wienhues, G., Temoltzin-Loranca, Y., Vogel, H., and Grosjean, M.: New sedimentological evidence of Lake Victoria’s palaeohydrological variability during the last deglacial transition (16-10 kyr BP), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7105, https://doi.org/10.5194/egusphere-egu22-7105, 2022.

EGU22-2788 | Presentations | CL1.2.1

Postglacial fire regime changes and vegetation dynamics at Lake Victoria, Africa

Yunuén Temoltzin-Loranca, Erika Gobet, Boris Vannière, Jacqueline F.N. van Leeuwen, Colin Courtney-Mustaphi, Giulia Wienhues, Sönke Szidat, Martin Grosjean, and Willy Tinner

Lake Victoria is the largest tropical lake on the planet. Located in East Africa at an altitude of 1135 m asl, it lies across the limits between two major climatic zones with a temperature and moisture gradient and associated tropical biomes, the rain forest, and the savanna. At higher altitudes > 1200–2500 m a.s.l. temperatures are significantly lower and vegetation forms an Afromontane belt. Primarily triggered by climate shifts, these three biomes and fire regimes have been dynamically interspersing over the last 17,000 years.

Here, we present a robust 14C chronology mainly based on macroscopic charcoal using the MICADAS system of LARA at the University of Bern, new palynological data used as biostratigraphic control, and the first continuous charcoal record in Lake Victoria to establish the fire history.

Our pollen and macro–charcoal records, support the assumption that throughout time regional fire dynamics are controlled by biome’s changes, and that climate was the main driver of these vegetation shifts at least until the Iron Age. Our results indicate that during the Last Glacial Maxima and Heinrich Stadial 1, under dry and colder climates the savanna was dominating, with low fire regimes before 15,000 cal yr BP and increased fire occurrence between 15,000 and 14,000 cal yr BP. After this period, the Afromontane forest started to expand, and warmer and humid climates promoted the growth of rain forests and reduced fire events, which is particularly observed in the African Humid Period (between ca. 11,500 and 5000 cal yr BP). Subsequently, our records indicate a global maximum of fire occurrence at 5000 cal yr BP, followed by unexpectedly low fire regimes during the Iron Age and the subsequent periods.

This work is part of a SINERGIA project funded by the Swiss National Foundation which seeks to unravel the long-term causes and consequences of Lake Victoria’s ecosystem dynamics with a special focus on the evolution of fish species and other biotas from the late Pleistocene to the present.

How to cite: Temoltzin-Loranca, Y., Gobet, E., Vannière, B., van Leeuwen, J. F. N., Courtney-Mustaphi, C., Wienhues, G., Szidat, S., Grosjean, M., and Tinner, W.: Postglacial fire regime changes and vegetation dynamics at Lake Victoria, Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2788, https://doi.org/10.5194/egusphere-egu22-2788, 2022.

EGU22-402 | Presentations | CL1.2.1

Sedimentary facies analysis and palaeoenvironmental reconstruction of the Kalkkop palaeolake, Eastern Cape, South Africa

Loyce Elesia Mpangala, Kelly Kirsten, Torsten Haberzettl, May Murungi, Silindokuhle Mavuso, and Robyn Pickering

Drilling undertaken in the 1990s at the Kalkkop impact crater, situated in the semi-arid, Nama-Karoo biome of South Africa, revealed lacustrine sedimentary deposits. This is an invaluable archive for a region synonymous with a paucity of terrestrial-based, continuous, and high-resolution records. In 2019, a new 90 m core was retrieved from the palaeolake and subjected to a detailed sedimentological log. Sedimentary facies analysis was applied to investigate the changes in past depositional environments, themselves reflecting local changes in hydroclimate. Sedimentological evidence indicated deposition in an overall low-energy environment, intermittently interrupted by brief high energy events. Employment of grey scale image analysis on the top 20 m revealed dry conditions persisted for longer and became more frequent towards the present surface. This was inferred by the darker layers referring to more minerogenic input which is associated with wetter conditions and lighter layers suggesting more pure carbonates and linked to dry conditions. This prolonged aridity impacted the longevity and alkalinity of the Kalkkop lake, resulting in carbonate precipitation, silica dissolution, and complete desiccation. Limited biological remains (diatoms, n=5) support this hypothesis. The body of evidence, namely carbonate precipitation and long persistence of arid spells, as well as the extremely low abundance of silica-based biological remains (pollen, diatoms, phytoliths), supports a transition toward a semi-arid environment by ~250 ka. This remarkable new record of past environmental and climatic changes recorded by the Kalkkop palaeolake core is the subject of ongoing research at the University of Cape Town, South Africa.

How to cite: Mpangala, L. E., Kirsten, K., Haberzettl, T., Murungi, M., Mavuso, S., and Pickering, R.: Sedimentary facies analysis and palaeoenvironmental reconstruction of the Kalkkop palaeolake, Eastern Cape, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-402, https://doi.org/10.5194/egusphere-egu22-402, 2022.

EGU22-557 | Presentations | CL1.2.1

Past plants to past vegetation and climate: the use of phytolith analysis in Stone Age deposits in South Africa

May Murungi

EGU22-606 | Presentations | CL1.2.1

Modeling Holocene paleoclimate of Konya basin and comparison with proxy data

Neriman Erdem and Bülent Arıkan

 

Konya closed basin, located on the Anatolian plateau, hosted plenty of cultures and civilizations throughout the Holocene. The abundance of archaeological settlements and the current ecological fragility of the basin have increased the scholarly focus on the region. The basin offers a long-term and multi-dimensional record of human-environment interactions that reflect social, environmental, political, and economic processes. Paleolimnology studies are significant to reconstruct the paleoclimate and the paleoenvironment of the region. Sediment cores obtained from the basin, which is known to be paleo lake formerly and its surrounding lakes, provide multiple proxy records. Although plenty of paleoenvironmental studies were conducted in the region, reaching a temporally and regionally homogenous and long-term dataset is not straightforward. First, this research aims to build a paleoenvironmental synthesis of the Konya Basin. Secondly, it aims to reveal the climatic changes in the region throughout the Holocene quantitatively. In this study, Macrophysical Climate Model (MCM) was run with thirty years of observation data from a total of 20 meteorological stations located in and around the study area. The model outputs were compared with the local proxy records (oxygen isotopes and pollen records) obtained from the lacustrine environments of the region. MCM is a heat-budget modeling method to precisely recognize the mean centers of high and low sea-level pressure systems that manage the weather and wind patterns at mid-latitudes. The MCM model allows us to predict meteorological parameters at the interval of 100 years from the present to 40,000 years ago. Preliminary findings from the MCM point to the wetter and warmer periods in the Early Holocene, similar to isotope proxies in the region. Towards the end of the Early Holocene, precipitation decreases, and the driest climatic conditions occur in the Middle Holocene. The model outputs confirm the cessation of the active alluvion process in the Middle Holocene, which was experienced due to the reduction in the seasonality of precipitation. It was seen that increasing trend in winter temperatures during the Holocene for analyzed stations. On the advancing parts of the research, the findings from this study will be used in an agent-based modeling platform to understand the complex human-environment interaction in the region.

How to cite: Erdem, N. and Arıkan, B.: Modeling Holocene paleoclimate of Konya basin and comparison with proxy data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-606, https://doi.org/10.5194/egusphere-egu22-606, 2022.

EGU22-10011 | Presentations | CL1.2.1

Is there an orbital control on the pacing of anoxia across the Aptian-Albian boundary (~113 Ma)?

Mathieu Martinez, Fatima-Zahra Ait-Itto, Danny Boué, Jean-Francois Deconinck, and Stéphane Bodin

The stratigraphic interval spanning the Aptian-Albian transition is marked by a cluster of short-lived marine anoxic episodes referred to as Oceanic Anoxic Event 1b (OAE 1b). These short-lived episodes are, from the oldest to the youngest, the Jacob, Kilian, Paquier and Leenhardt events. We here aim at testing the impact of the long Milankovitch cycles (1.2-Myr and 2.4-Myr) on the recurrence of these oxygen-deficiency episodes by establishing a precise astrochronology of the OAE 1b interval from the Col de Pré-Guittard section (Albian GSSP, Vocontian Basin, SE France). The section belongs to the “Marnes Bleues Formation”, which is a thick (several hundred metres) clayey formation, interrupted by thin limestone beds and black shale layers, slumps and turbidites, all deposited in the hemipelagic part of the Vocontian Basin. Organic-matter carbon isotope ratios and Total Organic Carbon have been measured to precisely locate these events within the Col de Pré-Guittard section. A magnetic susceptibility signal was obtained from 3500 bulk rock samples collected every 5 cm. The sampling was performed on two parts of the Col de Pré-Guittard section to avoid a multi-decametric slump outcropping in one of the two section below the Kilian Level. However, two thin turbidite layers, near the Jacob and the Paquier events, remained unavoidable. Spectral analyses were performed using the Multi-Taper Method and the evolutive Fourier Transforms. These spectral analyses show the pervasive control of the 100-kyr eccentricity cycle and demonstrates a duration of (i) 1.6 Myr from the Jacob to the Kilian events, (ii) 1.5 Myr from the Kilian to the Paquier events, and (iii) 1.0 Myr from the Paquier to the Leenhardt events. Duration do not correspond to long Milankovitch cycles and thus do not favour the sole orbital control on the pacing of the anoxic events of the Aptian-Albian transition. Thus, other global forcing factors, as the volcanism, or local factors, as basin-scale paleoceanographic and climatic changes, have to be considered to explain this recurrence of anoxic conditions in the Vocontian Basin.

How to cite: Martinez, M., Ait-Itto, F.-Z., Boué, D., Deconinck, J.-F., and Bodin, S.: Is there an orbital control on the pacing of anoxia across the Aptian-Albian boundary (~113 Ma)?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10011, https://doi.org/10.5194/egusphere-egu22-10011, 2022.

CL1.2.2 – Interdisciplinary Tree-Ring Research

EGU22-3077 | Presentations | CL1.2.2

Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests

Kristina Anderson-Teixeira and the ForestGEO dendrochronology team

Tree rings provide an invaluable long-term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree-ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree's growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3-month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3-month seasonal windows), with concave-down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible.

How to cite: Anderson-Teixeira, K. and the ForestGEO dendrochronology team: Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3077, https://doi.org/10.5194/egusphere-egu22-3077, 2022.

EGU22-3881 | Presentations | CL1.2.2

Drought legacy effects in radial tree growth are rarely significant under heightened statistical scrutiny

Stefan Klesse, Flurin Babst, Margaret E.K. Evans, Alexander Hurley, Christoforos Pappas, and Richard L. Peters

Drought legacy effects in radial tree growth have been extensively studied over the last decade and are found to critically influence carbon sequestration in woody biomass. Typically quantified as a deviation from “normal” growth, drought legacy magnitude and statistical significance depend on the definition of expected vs. unexpected growth variability under average conditions – a definition that has received insufficient theoretical validation.

Here, we revisit popular legacy effect analyses using the International Tree-Ring Data Bank (ITRDB) and employ a synthetic data simulation to disentangle four key variables influencing the magnitude of legacy effects. We show that legacy effects i) are mainly influenced by the overall auto-correlation of radial growth time series, ii) depend on climate-growth cross-correlation, iii) are directly proportional to the year-to-year variability of the growth time series, and iv) scale with the chosen extreme event threshold. Our analysis revealed that legacy effects are a direct outcome of the omnipresent biological memory.

We further found that the interpretation of legacy effects following individual drought events at specific sites is challenged by high stochasticity, and show that the commonly perceived stronger legacy effects for conifers are the result of higher auto-correlation compared to deciduous broadleaves. Given that the existing literature has not sufficiently addressed biological memory, we present two pathways to improve future assessment and interpretation of legacy effects. First, we provide a simulation algorithm to a posteriori account for auto-correlated residuals of the initial regression model between growth and climate, i.e. a corrected Null model to determine statistical significance, thereby retrospectively adjusting expectations for “normal” growth variability. The second pathway is to a priori include lagged climate parameters in the regression model. This substantially reduces the magnitude of observed legacy effects and thus challenges us to revisit estimates of drought-induced growth deviations by considering the full spectrum of expected growth behavior. 

How to cite: Klesse, S., Babst, F., Evans, M. E. K., Hurley, A., Pappas, C., and Peters, R. L.: Drought legacy effects in radial tree growth are rarely significant under heightened statistical scrutiny, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3881, https://doi.org/10.5194/egusphere-egu22-3881, 2022.

EGU22-6271 | Presentations | CL1.2.2

Impacts of the 2018-2019 drought: cumulative growth and stress responses in a floodplain forest ecosystem

Florian Schnabel, Sarah Purrucker, Lara Schmitt, Rolf A. Engelmann, Anja Kahl, Ronny Richter, Carolin Seele-Dilbat, Georgios Skiadaresis, and Christian Wirth

Intensifying climate change is successively increasing the frequency and intensity of extreme climate events such as droughts. In 2018–2019, Central European forests were hit by two consecutive hotter drought years that were unprecedented in their severity at least in the last 250 years. Such hotter droughts, where drought coincides with a heat wave, may have severe detrimental impacts on forest ecosystems as highlighted by reports of widespread tree defoliation and mortality across Central Europe in 2018–2019. Here, we examine the effect of this unprecedented event on tree growth and physiological stress responses (measured as increase in wood carbon isotope composition, Δδ13C) in a Central European floodplain forest ecosystem. We used tree rings of the dominant tree species Quercus robur, Acer pseudoplatanus and Fraxinus excelsior to compare growth responses, Δδ13C and drought legacy effects during the consecutive drought years 2018–2019 with effects observed in former single drought years (2003, 2006, 2015). We found that tree growth was, except for F. excelsior, not reduced in 2018 and that drought responses in 2018 were comparable to responses in former single drought years. This indicates that water availability in floodplain forests can partly buffer drought effects and meteorological water deficits. Nonetheless, the 2018 drought – which was the hottest and driest year since the start of records – induced drought legacies in tree growth while former drought years did not. Consistent with this observation, all tree species showed strong decreases in growth and increases in Δδ13C in the second hotter drought year 2019. The observed stress responses in 2019 were stronger than in any other examined drought year. We posit that the cumulative effect of two consecutive hotter drought years likely caused this unprecedented stress response across all species. Drought responses were consistent for both drought-stress indicators (growth response and Δδ13C), but the timing and magnitude of responses were species-specific: Q. robur exhibited the overall smallest response, followed by A. pseudoplatanus with the strongest response in F. excelsior. We discuss these species-specific differences in light of the species’ stomatal control (inferred from high-resolution sap flow measurements during drought at our site) and species’ resistance to xylem cavitation. Overall, our findings highlight that consecutive hotter droughts constitute a novel threat to forests, even in floodplain forests with comparably high levels of water supply. These results and similar research may contribute towards understanding and forecasting tree species responses to more frequent hotter droughts under intensifying climate change.

How to cite: Schnabel, F., Purrucker, S., Schmitt, L., Engelmann, R. A., Kahl, A., Richter, R., Seele-Dilbat, C., Skiadaresis, G., and Wirth, C.: Impacts of the 2018-2019 drought: cumulative growth and stress responses in a floodplain forest ecosystem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6271, https://doi.org/10.5194/egusphere-egu22-6271, 2022.

EGU22-4552 | Presentations | CL1.2.2

Using a process-based dendroclimatic proxy system model in a data assimilation framework: a test case in the Southern Hemisphere over the past centuries

Jeanne Rezsöhazy, Quentin Dalaiden, François Klein, Hugues Goosse, and Joël Guiot

Tree-ring widths represent the most commonly used proxy to reconstruct the climate of the last millennium at high resolution, thanks to their large-scale availability. The approach often relies on a relationship between tree-ring width series and climate estimated on the basis of a linear regression. The underlying linearity and stationarity assumptions may be inadequate. Dendroclimatic process-based models, such as MAIDEN (Modeling and Analysis In DENdroecology), may be able to overcome some of the limitations of the statistical approach. MAIDEN is a mechanistic ecophysiological model that simulates tree-ring growth starting from surface air temperature, precipitation and CO2 concentration daily inputs. In this study, we successfully include the MAIDEN model into a data assimilation procedure as a proxy system model to robustly compare the outputs of an Earth system model with tree-ring width observations and provide a spatially-gridded reconstruction of continental temperature, precipitation and winds in the mid to high latitudes of the Southern Hemisphere over the past centuries. More specifically, we evaluate the benefits of using process-based tree-growth models such as MAIDEN for reconstructing past climate with data assimilation compared to the commonly used linear regression. The comparison of the reconstructions with instrumental data indicates an equivalent skill of both the regression- and process-based proxy system models in the data assimilation framework. Nevertheless, the MAIDEN model still brings important advantages that could result in more robust reconstructions beyond the instrumental era. Moreover, improvements continuously made in such models or in their calibration procedure also offer encouraging perspectives. Important steps have thus been made to demonstrate that using a process-based model like MAIDEN as a proxy system model is a promising way to improve the large-scale climate reconstructions with data assimilation.

How to cite: Rezsöhazy, J., Dalaiden, Q., Klein, F., Goosse, H., and Guiot, J.: Using a process-based dendroclimatic proxy system model in a data assimilation framework: a test case in the Southern Hemisphere over the past centuries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4552, https://doi.org/10.5194/egusphere-egu22-4552, 2022.

EGU22-6899 | Presentations | CL1.2.2

Piloting novel multi-centennial palaeoclimate records from mainland southeast Australia.

Jacinda O'Connor, Benjamin Henley, Matthew Brookhouse, and Kathryn Allen

High-resolution palaeoclimate proxies are fundamental to our understanding of the diverse climatic history of the Australian mainland, particularly given the deficiency in instrumental datasets spanning greater than a century. Annually resolved, tree-ring based proxies play a unique role in addressing limitations in our knowledge of interannual to multi-decadal temperature and hydroclimatic variability prior to the instrumental period. Here we present cross-dated ring-width (RW) and minimum blue-intensity (BI) chronologies spanning 70 years (1929 – 1998) for Podocarpus lawrencei Hook.f., the Australian mainland's only alpine conifer, based on nine full-disk cross-sections from Mount Loch in the Victorian Alps. Correlations with climate variables from observation stations and gridded data reveal a significant positive relationship between RW and mean monthly maximum temperatures in winter throughout central Victoria (r = 0.62, p < 0.001), and a significant negative correlation to winter precipitation (r = -0.51, p < 0.001). We also found significant negative correlations between RW and monthly snow depth data from Spencer Creek in New South Wales (r = -0.60, p < 0.001). Of the assessed BI parameters, delta blue-intensity (ΔBI; the difference between early- and late-wood BI) displayed the greatest sensitivity to climate, with robust spatial correlations with mean October to December maximum and minimum monthly temperatures (r = -0.43, p < 0.001; r = -0.51, p < 0.001) and July precipitation (r = 0.44, p < 0.001), across large areas of northern V