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1. Late Holocene droughts and cave ice harvesting by Ancestral Puebloans

   https://doi.org/10.1038/s41598-020-76988-1  

   Onac, Bogdan P. ; Baumann, Steven M. ; Parmenter, Dylan S. ; Weaver, Eric ; Sava, Tiberiu B. ( December 2020 , Scientific Reports)

   null (Ed.)

   Abstract Water availability for Native Americans in the southwestern United States during periods of prolonged droughts is poorly understood as regional hydroclimate records are scant or contradicting. Here, we show that radiocarbon-dated charcoal recovered from an ice deposit accumulated in Cave 29, western New Mexico, provide unambiguous evidence for five drought events that impacted the Ancestral Puebloan society between ~ AD 150 and 950. The presence of abundant charred material in this cave indicates that they periodically obtained drinking water by using fire to melt cave ice, and sheds light on one of many human–environment interactions in the Southwest in a context when climate change forced growing Ancestral Puebloan populations to exploit water resources in unexpected locations. The melting of cave ice under current climate conditions is both uncovering and threatening a fragile source of paleoenvironmental and archaeological evidence of human adaptations to a seemingly marginal environment. 

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2. Evaluating the Drivers of Quaternary Dust Fluxes to the Western North Pacific: East Asian Dustiness and Northern Hemisphere Gustiness

   https://doi.org/10.1029/2022PA004571  

   Abell, Jordan T. ; Winckler, Gisela ; Pullen, Alex ; Kinsley, Christopher W. ; Kapp, Paul A. ; Middleton, Jennifer L. ; Pavia, Frank J. ; McGee, David ; Ford, Heather L. ; Raymo, Maureen E. ( September 2023 , Paleoceanography and Paleoclimatology)

   Quantifying variability in, and identifying the mechanisms behind, East Asian dust production and transport across the last several million years is essential for constraining future dust emissions and deposition. Our current understanding of East Asian dust dynamics through the Quaternary is primarily limited to low‐resolution records from the North Pacific Ocean, those from the Chinese Loess Plateau (CLP), and paleoenvironmental reconstructions from arid basins. All are susceptible to sediment winnowing and focusing as well as input of poorly constrained or unidentified non‐dust detrital material. To avoid these limitations, we examine high‐resolution, constant flux proxy‐derived dust fluxes from the North Pacific and find evidence for higher glacial dust fluxes in the late Pliocene‐early Pleistocene compared to the late Pleistocene‐Holocene. Our results suggest decreasing dust transported to the mid‐latitude North Pacific Ocean from eastern Asia across the Quaternary. This observation is ostensibly at odds with previous dust records from marine sediments and the CLP, and with the perception of higher East Asian dust production and transport during the late Pleistocene associated with the amplification of glaciations. We provide three possible scenarios to describe the ∼2,700‐ky evolution of eastern Asia glacial dust dynamics, and discuss them in the context of sediment production, availability, and atmospheric circulation. Our data and proposed driving mechanisms not only raise questions about the framework typically used to interpret dust archives from East Asia and the North Pacific Ocean, but also provide a roadmap for hypothesis testing and future work necessary to produce better‐constrained records of paleo‐dust fluxes.

    

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3. Comparing the paleoclimates of northwestern and southwestern Madagascar during the late Holocene: Implications for the role of climate in megafaunal extinction

   Faina, P. ; Burns, S. J. ; Godfrey, L.R. ; Crowley, B.E. ; Scroxton, N. ; McGee, D. ; Sutherland, M.R. ; Ranivoharimanana, L. ( January 2021 , Malagasy nature)

   The relative importance of climate and humans in the disappearance of the Malagasy megafauna remains under debate. Data from southwestern Madagascar imply aridification contributed substantially to the late Holocene decline of the megafauna (the Aridification Hypothesis). Evidence for aridification includes carbon isotopes from tree rings, lacustrine charcoal concentrations and pollen assemblages, and changes in fossil vertebrate assemblages indicative of a local loss of pluvial conditions. In contrast, speleothem records from northwestern Madagascar suggest that megafaunal decline and habitat change resulted primarily from human activity including agropastoralism (the Subsistence Shift Hypothesis). Could there have been contrasting mechanisms of decline in different parts of Madagascar? Or are we lacking the precisely dated, high resolution records needed to fully understand the complex processes behind megafaunal decline? Reconciling these contrasting hypotheses requires additional climate records from southwestern Madagascar. We recovered a stalagmite (AF2) from Asafora Cave in the spiny thicket ecoregion, ~10 km from the southwest coast and just southeast of the Velondriake Marine Reserve. U-series and 14C dating of samples taken from the core of this stalagmite provide a highly precise chronology of the changes in hydroclimate and vegetation in this region over the past 3000 years. Speleothem stable oxygen and carbon isotope analyses provide insight into past rainfall variability and vegetation changes respectively. We compare these records with those for a stalagmite (AB2) from Anjohibe Cave in northwestern Madagascar. Lastly, odds ratio analyses of radiocarbon dates for extinct and extant subfossils allow us to describe and compare the temporal trajectories of megafaunal decline in the southwest and the northwest. Combined, these analyses allow us to test the Aridification Hypothesis for megafaunal extinction. The trajectories of megafaunal decline differed in northwestern and southwestern Madagascar. In the southwest, unlike the northwest, there is no evidence of decoupling of speleothem stable carbon and oxygen isotopes. Instead, habitat changes in the southwest were largely related to variation in hydroclimate (including a prolonged drought). The megafaunal collapse here occurred in tandem with the drought, and agropastoralism likely contributed to that demise only after the megafauna had already suffered drought-related population reduction. Our results offer some support for the Aridification Hypothesis, but with three caveats: first, that there was no island-wide aridification; second, that aridification likely impacted megafaunal decline only in the driest parts of Madagascar; and third, that aridification was not the sole factor promotingmegafaunal decline even in the dry southwest. A number of megafaunal species survived the prolonged drought of the first millennium, and then likely succumbed to the activities of agropastoralists. 

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4. Comparing the paleoclimates of northwestern and southwestern Madagascar during the late Holocene: implications for the role of climate in megafaunal extinction

   Faina, P. ; Burns, S.J. ; Godfrey, L.R. ; Crowley, B.E. ; Scroxton, N. ; McGee, D. ; Sutherland, M.R. ; Ranivoharimanana, L. ( December 2021 , Malagasy nature)

   The relative importance of climate and humans in the disappearance of the Malagasy megafauna remains under debate. Data from southwestern Madagascar imply aridification contributed substantially to the late Holocene decline of the megafauna (the Aridification Hypothesis). Evidence for aridification includes carbon isotopes from tree rings, lacustrine charcoal concentrations and pollen assemblages, and changes in fossil vertebrate assemblages indicative of a local loss of pluvial conditions. In contrast, speleothem records from northwestern Madagascar suggest that megafaunal decline and habitat change resulted primarily from human activity including agropastoralism (the Subsistence Shift Hypothesis). Could there have been contrasting mechanisms of decline in different parts of Madagascar? Or are we lacking the precisely dated, high resolution records needed to fully understand the complex processes behind megafaunal decline? Reconciling these contrasting hypotheses requires additional climate records from southwestern Madagascar. We recovered a stalagmite (AF2) from Asafora Cave in the spiny thicket ecoregion, ~10 km from the southwest coast and just southeast of the Velondriake Marine Reserve. U-series and 14C dating of samples taken from the core of this stalagmite provide a highly precise chronology of the changes in hydroclimate and vegetation in this region over the past 3000 years. Speleothem stable oxygen and carbon isotope analyses provide insight into past rainfall variability and vegetation changes respectively. We compare these records with those for a stalagmite (AB2) from Anjohibe Cave in northwestern Madagascar. Lastly, odds ratio analyses of radiocarbon dates for extinct and extant subfossils allow us to describe and compare the temporal trajectories of megafaunal decline in the southwest and the northwest. Combined, these analyses allow us to test the Aridification Hypothesis for megafaunal extinction. 

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5. Cave life histories of non-anthropogenic sediments help us understand associated archaeological contexts

   https://doi.org/10.1017/qua.2020.72  

   Karkanas, Panagiotis ; Marean, Curtis ; Bar-Matthews, Mira ; Jacobs, Zenobia ; Fisher, Eric ; Braun, Kerstin ( January 2021 , Quaternary Research)

   Abstract Pinnacle Point (PP) near Mossel Bay in the Western Cape Province, South Africa, is known for a series of archaeological caves with important archaeological finds. Extensive excavations and studies in two of them (PP13B and PP5-6) have documented alternating periods of anthropogenic-dominated and geogenic-dominated sedimentation. A variety of caves do not bear evidence of anthropogenic remains. We have studied in detail the remnant deposits of three of them, Staircase Cave, Crevice Cave, and PP29, which have been formed under the same geologic and sedimentary conditions with those with anthropogenic contributions. Their remains are small and patchy but have extensive speleothem formations (as do most caves at PP) that were isotopically analyzed for paleoclimate and paleoenvironmental reconstruction. These caves also offer the opportunity to understand the purely geogenic signature of the PP locality and thus offer a geogenic baseline for the anthropogenic caves. Archaeologists normally focus only on sites with strong anthropogenic signals, but by building cave life histories we “raise the bar” (Goldberg 2008, p. 30) on our contextual knowledge. 

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