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1. An abrupt temperature and hydroclimate transition in eastern Africa during Termination V

   Ramirez, B.; Castañeda, I.S.; Salacup, J.M.; Johnson, T.C. (July 2023, XXI INQUA Congress)

   Over the last few million years, Africa’s climate exhibits a long-term drying trend with episodes of high climate variability coinciding with the intensification of glacial-interglacial cycles. Of particular interest, is a shift to drier and more variable conditions noted in the Olorgesailie Formation (Kenya) between 500 and 300 thousand years ago (ka) in which Potts et al. (2018) observed a turnover of ~85% of large-body mammalian fauna to smaller-body related taxa and suggested that the shift was an evolutionary response to better adapt to the changing climate. However, an erosional gap in the Olorgesailie record during this time interval means that the cause of this faunal shift is still an outstanding question. To understand East African climate variability during the Mid-Pleistocene, we analyze Lake Malawi drill core MAL 05–1 (~11ºS, 34ºE) to investigate if a specific climatic event stands out as a possible driver of the dramatic change observed in the East African mammal community. We use organic geochemical proxies including branched glycerol diaklyl glycerol tetraethers (brGDGTs; the MBT′5ME index) andleaf wax carbon and deuterium isotopes to develop high-resolution temperature, vegetation, and precipitation records, respectively, between 600 and 200 ka. Results show an abrupt temperature increase of ~9°C occurring in less than 3000 years during Glacial Termination V, which is the Marine Isotope Stage (MIS) 12 to MIS 11 transition at ~330 ka. Preliminary leaf wax deuterium isotopic values show an enrichment that coincides with deglacial warmings suggesting a shift to more arid conditions during interglacial than in glacial periods. This change from a cold/wet glacial to a warm/dry interglacial contrast with the cool/dry pattern of the Last Glacial Maximum (LGM) in East Africa which transitioned to a warm/wet Holocene. Leaf wax carbon isotopes are presently being analyzed to understand past shifts in C3 vs C4 vegetation type, which can be related to climatic conditions. We propose that the major warming and drying during Termination V in East Africa represents a significant abrupt change in the climate of eastern Africa and was a likely driver of the major faunal turnover noted in the region. 

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2. Late Pleistocene drivers of climate and vegetation in the Western Sahel from leaf wax biomarker isotopes

   Lupien, Rachel (June 2022, Abstracts American Quaternary Association National Conference)

   The Sahel is highly sensitive to flooding, droughts, and wildfires, risking food and other resources on which nearly 100 million people depend. Understanding how natural variations of precipitation and vegetation fluctuate during high-amplitude glacial- interglacial cycles can help constrain the regional sensitivity to a wide range of external forcings. Further, the interactions between climate and ecosystem changes remain uncertain for sub-Saharan Africa due to the lack of long, highly-resolved, quantitative, terrestrial records. Here we present precipitation and vegetation records from ~215 ka to present, derived from long leaf wax hydrogen (δDwax) and carbon (δ13Cwax) isotopes, respectively. These geochemical records are derived from ODP Site 959 in the Gulf of Guinea, where westerly winds and major river systems transport Western Sahel-sourced terrestrial leaf waxes. We find that, unlike many African records that are precessionally- driven, obliquity plays an important role in West African late Pleistocene hydroclimate, suggesting that a cross-equatorial insolation gradient may be more important in this area and certainly that drivers of orbital-scale precipitation change are regionally-specific. Further, vegetation changes appear to have a complex relationship with hydroclimate over this mid-late Pleistocene interval. A potential shift in this climate-environment coupling at MIS6 ~130 ka, which is a time when there is also a shift in forcing mechanisms in East Africa, suggests that the global boundary condition changes associated with large glacial- interglacial cycling may affect equatorial climate. 

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3. Precise timing of MIS 7 substages from the Austrian Alps

   https://doi.org/10.5194/cp-17-1443-2021  

   Wendt, Kathleen A.; Li, Xianglei; Edwards, R. Lawrence; Cheng, Hai; Spötl, Christoph (January 2021, Climate of the Past)

   null (Ed.)

   Abstract. Investigating the precise timing of regional-scale climate changes during glacial terminations and the interglacial periods that follow is key tounraveling the mechanisms behind these global climate shifts. Here, we present a high-precision time series of climate changes in the Austrian Alpsthat coincide with the later portion of Termination III (TIII), the entire penultimate interglacial (Marine Isotope Stage (MIS) 7), Termination IIIa(TIIIa), and the penultimate glacial inception (MIS 7–6 transition). Using state-of-the-art mass spectrometry techniques, we have constructed auranium-series chronology with relative age uncertainties averaging 1.7 ‰ (2σ) for our study period (247 to 191 thousand yearsbefore present, ka). Results reveal the onset of warming in the Austrian Alps associated with TIII at 242.5 ± 0.2 ka and theduration of MIS 7e warming between 241.8 and 236.7 (±0.6) ka. An abrupt shift towards higher δ18O values at216.8 ka marks the onset of regional warming associated with TIIIa. Two periods of high δ18O values (greater than−10 ‰ Vienna Pee Dee Belemnite (VPDB)) between 215.9–213.3 and 204.3–197.5 (±0.4) ka coincide with interglacial substages MIS 7c and 7a,respectively. Multiple fluorescent inclusions suggest a partial retreat of the local Alpine glacier during peak obliquity forcings at214.3 ± 0.4 ka. Two newly collected stalagmites from Spannagel Cave (SPA146 and 183) provide high-resolution replications of thelatter portion of the MIS 7a-to-6e transition. The resulting multi-stalagmite record reveals important chronological constraints on climate shifts inthe Austrian Alps associated with MIS 7 while offering new insight into the timing of millennial-scale changes in the North Atlantic realm leadingup to TIII and TIIIa. 

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4. Changes in benthic foraminifera assemblage preservation associated with onset of deep AMOC during the last deglaciation

   Poirier, R. K.; Gaetano, M. Q.; Acevedo, K.; Kozdon, R.; Raymo, M. E. (October 2018, AGU Fall Meeting)

   Benthic foraminifera are used to generate the majority of paleo-proxy records reconstructing past ocean changes including variations in the strength of AMOC. To assess the reliability of geochemical proxy records generated using benthic foraminifera, a Foraminifera Preservation Index (FPI) was developed to quantify assemblage-wide changes in visual preservation quality. The qualitative criteria for preservation included in the FPI are supported by stable isotope and trace element datasets. Early application of the FPI on Cibicidoidesassemblages from the deep Pacific Ocean (IODP Sites 846, 1143, 1208) reveal quantifiably better preservation during glacial periods relative to interglacial periods for the last ~1 million years. Here, we present results from two summer REU projects tracking such preservation changes in the deep North and South Atlantic Ocean prior to and throughout the last deglaciation (~0-35 ka). Changes in Cibicidoides FPI from IODP Site 1089 in the deep South Atlantic (~4600m water depth: primarily bathed by Antarctic Bottom Water - AABW) mirror those in the Pacific with better preservation during the glacial maximum of Marine Isotope Stage (MIS 2) than the Holocene interglacial (MIS 1). Alternatively, Cibicidoides FPI from IODP Site 1059 (~3000m water depth: bathed by North Atlantic Deep Water [NADW] during interglacials; and by AABW during glacials) reveal better preservation during the Holocene relative to MIS 2. Despite these opposing trends, changes in FPI occur at both sites at ~15 ka corresponding to major changes to AMOC documented throughout the deep Atlantic basin. These findings imply that the same processes involved in water mass CO2-carbonate chemistry on glacial-interglacial timescales affect preservation of benthic foraminifera. Furthermore, our results suggest that the FPI can track major changes in deglacial AMOC, potentially providing an inexpensive method to produce preliminary data prior to or in unison with more expensive geochemical analyses. 

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5. Northward Shifts in the Polar Front Preceded Bølling and Holocene Warming in Southwestern Scandinavia

   https://doi.org/10.1029/2020GL088153  

   Cowling, O. C.; Thomas, E. K.; Svendsen, J. I.; Mangerud, J.; Vasskog, K.; Haflidason, H. (July 2020, Geophysical Research Letters)

   Abstract The last deglaciation in northern Europe provides an opportunity to study the hydrologic component of abrupt climate shifts in a region with complex interactions between ice sheets and oceanic and atmospheric circulation. We use leaf wax hydrogen isotopes (δ²H) to reconstruct summer precipitation δ²H and aridity in southwestern Norway from 15.8 to 11.5 ka. We identify transitions to a more proximal moisture source before the ends of Heinrich Stadial 1 and the Younger Dryas, prior to local warming and increased primary productivity in both instances. We infer these changes in moisture delivery to southwestern Norway to be a response to northward shifts in the polar front caused by warm water intrusion into the North Atlantic, which preceded abrupt warming in the circum‐North Atlantic. These results suggest that moisture transport pathways shift northward as warm surface ocean water reaches higher latitudes in the North Atlantic. 

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