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1. East African Climate During a Major Turnover in Mammal Species between 400 and 500 thousand years ago

   Johnson, T.; Ramirez, B.; Salacup, J.; Castañeda, I.S. (October 2022, Abstracts Geological Society of America)

   Roughly 85% of mammalian herbivore species in southern Kenya were replaced by smaller, more adaptable species at some time between 400,000 years ago (400ka) and 500 ka. While this major taxonomic turnover has been attributed to a shift to more a more arid and variable climate and tectonic activity, we wondered if a particularly abrupt shift, a “tipping point,” in climate at some time between 400 and 500 ka was the cause. We analyzed the highest resolution paleoclimate record available in East Africa, Lake Malawi drill core MAL05-1B, for organic geochemical proxies, including branched glycerol dialkyl glycerol tetraethers (GDGTs) and leaf wax deuterium isotopic records to develop the temperature and precipitation history, respectively, between 600 and 200 ka. Results show an abrupt temperature increase of ~6°C occurring in less than 3000 years during Glacial Termination V, which is the Marine Isotope Stage (MIS) 12 to MIS 11 transition at ~430 ka. Surprisingly, even more intense warming occurred during Glacial Termination VI around 510 ka. Notably, these deglacial warmings coincide with enriched leaf wax deuterium isotopic values suggesting a shift to more arid conditions in interglacials MIS 13 and 11 than in glacials MIS 14 and 12, respectively. These changes from cold/wet glacials to warm/dry interglacials contrast with the cool/dry pattern of the Last Glacial Maximum (LGM) in East Africa that transitioned to a warm/wet Holocene. We propose that the major warming and drying during Termination V in the Malawi basin represents a significant abrupt change that impacted much of eastern Africa around 430 ka and was a likely driver of the major faunal turnover noted in the region. 

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2. 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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3. MIDDLE PLEISTOCENE HYDROCLIMATE CHANGES IN THE TROPICAL ANDES INFERRED FROM CARBON AND OXYGEN ISOTOPE RECORDS OF SPELEOTHEMS FROM HUAGAPO CAVE, PERU

   https://doi.org/10.1130/abs/2023AM-394169  

   Olson, Elizabeth; Parmenter, Dylan; Gillikin, David; Stoltenberg, Hailey; Clavel, Avery; Piccirillo, Laura; Verheyden, Anouk; Edwards, Lawrence; Rodbell, Donald (January 2023, Geologic Society of America)

   Glacial-interglacial transitions and abrupt millennial-scale events are the most prominent features in many paleoclimate records. Understanding these oscillations requires high-resolution time series from multiple locations to constrain the latitudinal response to forcings. Few high-resolution records exist from the Southern Hemisphere tropics that predate the last two glaciations. We present a high-resolution speleothem oxygen and carbon isotope record from Huagapo Cave in the Central Peruvian Andes covering Marine Isotope Stage (MIS) 8 glacial and MIS 9 interglacial (339 to 249 ka). Uranium-series dates on three stalagmites (n=18) with small age uncertainty ±1% allows us to resolve abrupt climate events similar in structure and duration to Dansgaard-Oescchger and Heinrich events. The South American Summer Monsoon (SASM) controls modern hydroclimate variability in the Andes, and previous records from Huagapo Cave have provided records of past SASM variability. Termination three (T-III) in our record has a steep increase in δ18O values of 5‰, punctuated by two stadial event decreases of ~3‰ (S8.1 and S8.2). This pattern is mirrored in the δ13C record, indicating that these millennial-scale events record hydroclimate and vegetation productivity changes. The same structure as our T-III record is found in other records globally, where they are noted to be Heinrich-like events. Frequency analysis indicates that the occurrence of these abrupt events changes between glacial cycles. Precession is weakly expressed in the δ18O record during MIS 8; similar to speleothem records from the region dating to the Last Glacial Maximum (LGM). Global ice cover and sea levels were similar in the LGM and MIS 8, but the Milankovitch insolation forcing differed. This change in SASM behavior is not observed in the East Asian monsoon, where the precession signal is dominant throughout. Interglacial precessional control is apparent during the latter half of MIS 9 and during Huagapo Cave intervals dating to MIS 6 and 7. These data indicate that the response to high-latitude forcing in the Southern Hemisphere tropics fluctuates through time, and potential explanations for low-latitude sensitivity to forcing factors are further explored. 

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4. Moraines in the Austrian Alps record repeated phases of glacier stabilization through the Late Glacial and the Early Holocene

   https://doi.org/10.1038/s41598-022-12477-x  

   Braumann, Sandra M.; Schaefer, Joerg M.; Neuhuber, Stephanie; Fiebig, Markus (June 2022, Scientific Reports)

   Abstract Climate is currently warming due to anthropogenic impact on the Earth’s atmosphere. To better understand the processes and feedbacks within the climate system that underlie this accelerating warming trend, it is useful to examine past periods of abrupt climate change that were driven by natural forcings. Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate phases, focusing on the period between 15 and 10 ka. Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents in two glaciated valleys of the Silvretta Massif in the Austrian Alps. The mountain glacier record shows that general deglaciation after the Last Glacial Maximum (LGM) was repeatedly interrupted by glacier stabilization or readvance, perhaps during the Oldest Dryas to Bølling transition (landform age: 14.4 ± 1.0 ka) and certainly during the Younger Dryas (YD; 12.9–11.7 ka) and the Early Holocene (EH; 12–10 ka). The oldest landform age indicates a lateral ice margin that postdates the ‘Gschnitz’ stadial (ca. 17–16 ka) and predates the YD. It shows that local inner-alpine glaciers were more extensive until the onset of the Bølling warm phase (ca. 14.6 ka), or possibly even into the Bølling than during the subsequent YD. The second age group, ca. 80 m below the (pre-)Bølling ice margin, indicates glacier extents during the YD cold phase and captures the spatial and temporal fine structure of glacier retreat during this period. The ice surface lowered approximately 50–60 m through the YD, which is indicative of milder climate conditions at the end of the YD compared to its beginning. Finally, the third age group falls into a period of more substantial warming, the YD–EH transition, and shows discontinuous glacier retreat during the glacial to interglacial transition. The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif evidence multiple cold phases that punctuated the general post-LGM warming trend and illustrate the sensitive response of Silvretta glaciers to abrupt climate oscillations in the past. 

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5. Ocean Oxygenation Changes in the Arabian Sea Oxygen Minimum Zone During the Penultimate Glacial Cycle

   https://doi.org/10.1029/2024PA005059  

   Qian, Fang; Wang, Yi; Costa, Kassandra M; Nielsen, Sune G (June 2025, Paleoceanography and Paleoclimatology)

   Abstract Reconstructing past oxygen fluctuations in oxygen minimum zones (OMZs) is crucial for understanding their response to climate change. Numerous studies suggest better oxygenation in the Arabian Sea OMZ during the Last Glacial Maximum (LGM) compared to the Holocene. However, bottom water oxygen (BWO) variability during the Penultimate Glacial Cycle (Marine Isotope Stage [MIS] 6 to MIS 5e, ∼140–115 ka B.P.) remains poorly constrained. This study reconstructs BWO variations during this period from sediment core TN041‐8JPC in the western Arabian Sea OMZ, utilizing proxies including benthic foraminiferal surface porosity, redox‐sensitive trace metal enrichment factors (e.g., U_EF), and U/Ba ratios. Bottom water oxygen concentrations were 24.4 ± 5.9 μmol/kg during MIS 6 and 16.8 ± 6.5 μmol/kg during MIS 5e, with all proxies indicating higher BWO in MIS 6 than in MIS 5e. However, these proxies show different patterns within MIS 5e, indicating that U_EFand U/Ba ratios may be limited to recording average BWO in glacial and interglacial (quasi)steady states. We propose that the intensified OMZ during MIS 5e, relative to MIS 6, was driven by higher productivity, temperature‐induced reductions in oxygen solubility, and reduced delivery of Southern‐sourced intermediate waters. In contrast, the intensified OMZ during the Holocene, compared to the LGM, was likely influenced by lower oxygen solubility, reduced Southern water delivery, and winter convective mixing rather than productivity. This study highlights a general trend of weaker OMZs in glacial than interglacial periods, though the mechanisms may not be identical, offering insights into OMZ dynamics under climate change in the past. 

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