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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. Early Holocene Atmospheric Circulation Changes Over Northern Europe Based on Isotopic and Biomarker Evidence From Kola Peninsula

   https://doi.org/10.1029/2024PA005076  

   Holtzman, Hannah; Thomas, Elizabeth_K; Erb, Michael; Marshall, Leah; Castañeda, Isla_S; Kaufman, Darrell; McKay, Nicholas_P; Melles, Martin (March 2025, Paleoceanography and Paleoclimatology)

   Abstract Rapid Arctic warming this century will likely cause major water cycle and atmospheric circulation changes, including weakening mid‐latitude westerly winds and more persistent summer high pressures over Fennoscandia. These conditions can cause drought in northern Europe and extreme rainfall in the Mediterranean region. Uncertainties in the spatiotemporal patterns of these predictions can be partially addressed with records of past climate response to rapid change. The early Holocene collapse of the Northern Hemisphere ice sheets provides a natural experiment to evaluate the climate response to rapid changes in boundary conditions. We analyzed lipid biomarker distributions and hydrogen isotope (δ²H) values from Lake Imandra, Kola Peninsula, to infer Holocene summer temperature and summer precipitation δ²H values. Sensitivity tests of a lake model suggest summer precipitation δ²H values are the main mechanism influencing Lake Imandra δ²H values. Summer precipitation isotope values exhibited a nearly 20‰²H‐depletion between 8.6 and 8.0 ka, with²H ‐enriched values before 8.6 ka and²H ‐depleted values 8.0 ka to present. Maximum warmth occurred from 8.5 to 7.0 ka. Climate model experiments suggest that the early Holocene Laurentide Ice Sheet collapse caused a westward shift of the Fennoscandian summer high‐pressure center. This caused a decrease in the proportion of local,²H‐enriched precipitation falling throughout Fennoscandia and an increase in far‐traveled,²H‐depleted precipitation from the mid‐latitudes, circulation that persisted throughout the Holocene. These results illustrate the sensitivity of climate in Fennoscandia and show that circulation regime shifts can occur in response to changes in boundary conditions far upwind. 

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3. Last glacial maximum ecology and climate from terrestrial gastropod assemblages in Peoria loess, western Kentucky

   https://doi.org/10.1002/jqs.3206  

   Grimley, David_A; Counts, Ronald_C; Conroy, Jessica_L; Wang, Hong; Dendy, Sarah_N; Nield, Catherine_B (May 2020, Journal of Quaternary Science)

   ABSTRACT The Rocks loess section, in unglaciated western Kentucky, provides a high‐resolution environmental record during the last glacial maximum onset. The Peoria Silt (9 m thick) contains 26 terrestrial gastropod species, with up to 15 species within a single 5 cm interval. Thirteen radiocarbon ages, using shells or charcoal, range between 30 and 24.5 cal ka; younger loess has been leached or eroded. Stratigraphic shifts in gastropod assemblages imply significant cooling, particularly ~27 cal ka, as solar insolation was decreasing and the southern Laurentide Ice Sheet rapidly advancing. Midwestern to southern species (e.g.Anguispira kochi,Gastrocopta pentodon,Hawaii miniscula,Helicodiscus parallelus,Vallonia perspectiva) occur only in the lowermost Peoria Silt (~30–27 cal ka). In contrast, cold‐tolerant species (Columella alticola,Vertigo modesta, Vallonia gracilicosta)occur only in full glacial Peoria Silt (27–24.5 cal ka). Inferred mean July temperatures, from mutual climatic range methods, range from ~23 °C at 30 cal ka, cooling to ~18 °C by 26 cal ka; about 3–8 °C cooler than today (~26 °C). Superimposed on this cooling trend are multi‐centennial variations in detrital carbonate, fossil shell concentrations, palaeotemperature estimates, and oxygen isotope values (Vertigo,Discus, Helicodiscus). The finer‐scale variations imply relatively synchronous fluctuations in glacial sediment supply, loess sedimentation, and climate. 

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4. Reintroducing bison results in long-running and resilient increases in grassland diversity

   https://doi.org/10.1073/pnas.2210433119  

   Ratajczak, Zak; Collins, Scott L.; Blair, John M.; Koerner, Sally E.; Louthan, Allison M.; Smith, Melinda D.; Taylor, Jeffrey H.; Nippert, Jesse B. (September 2022, Proceedings of the National Academy of Sciences)

   The widespread extirpation of megafauna may have destabilized ecosystems and altered biodiversity globally. Most megafauna extinctions occurred before the modern record, leaving it unclear how their loss impacts current biodiversity. We report the long-term effects of reintroducing plains bison ( Bison bison ) in a tallgrass prairie versus two land uses that commonly occur in many North American grasslands: 1) no grazing and 2) intensive growing-season grazing by domesticated cattle ( Bos taurus ). Compared to ungrazed areas, reintroducing bison increased native plant species richness by 103% at local scales (10 m 2 ) and 86% at the catchment scale. Gains in richness continued for 29 y and were resilient to the most extreme drought in four decades. These gains are now among the largest recorded increases in species richness due to grazing in grasslands globally. Grazing by domestic cattle also increased native plant species richness, but by less than half as much as bison. This study indicates that some ecosystems maintain a latent potential for increased native plant species richness following the reintroduction of native herbivores, which was unmatched by domesticated grazers. Native-grazer gains in richness were resilient to an extreme drought, a pressure likely to become more common under future global environmental change. 

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5. 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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