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1. A new MIS 5 to MIS 2 speleothem record from Sandkraal Cave on the South African Cape south coast

   https://doi.org/10.1017/qua.2024.3  

   Braun, Kerstin; Bar-Matthews, Miryam; Ayalon, Avner; Matthews, Alan; Zilberman, Tami; Zolotova, Natalya; Cowling, Richard M.; Karkanas, Panagiotis; Cawthra, Hayley C.; Fisher, Erich C.; et al (March 2024, Quaternary Research)

   Abstract We present new stable oxygen and carbon isotope composite records (δ¹⁸O, δ¹³C) of speleothems from Sandkraal Cave 1 (SK1) on the South African south coast for the time interval between 104 and 18 ka (with a hiatus between 48 and 41 ka). Statistical comparisons using kernel-based correlation analyses and semblance analyses based on continuous wavelet transforms inform the relationships of the new speleothem records to other proxies and their changes through time. Between 105 and ~70 ka, changes of speleothem δ¹⁸O values at SK1 are likely related to rainfall seasonality. Variations of δ¹³C values are associated with changes of vegetation density, prior carbonate precipitation (PCP), CO₂degassing in the cave, and possibly variations of the abundance of C₃and C₄grasses in the vegetation. The relationships of δ¹⁸O with other proxies shift between ~70 and 48 ka (Marine Isotope Stages 4–3) so that both stable isotope records now reflect CO₂degassing, evaporation, and PCP. Similar relationships also continue after the hiatus for the deposition phase between 42 and 18 ka. Our findings support modeling results suggesting drier conditions in the study area when the Southern Hemisphere westerlies are shifted north and the paleo–Agulhas Plain is exposed. 

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2. Cave monitoring in the Peruvian Andes reveals monsoon climate preserved in speleothem calcite

   https://doi.org/10.1016/j.chemgeo.2024.122315  

   Olson, Elizabeth; Gillikin, David P; Piccirillo, Laura; Verheyden, Anouk; Forsyth, Alexander; Litchfield, Kirsten; Stoltenberg, Hailey; Clavel, Avery; Ramjohn, Maryam; Nazir, Saliha; et al (November 2024, Chemical Geology)

   NA (Ed.)

   Speleothem paleoclimate records from the Peruvian Andes have been interpreted to reflect the strength of the South American monsoon. While these interpretations have been verified through comparison with other regional and global climate records, the mechanics of the cave environment that facilitate the preservation of this signal with such consistency remain unstudied. Here, we present four years of environmental data from Huagapo and Pacupahuain cave, and one year from Antipayarguna cave. The data reveal that the cave environment is very stable with little to no change in temperature and 100% relative humidity year-round. This stability in cave air is juxtaposed with the monsoonal drip water pulse that increases drip rates over 40 times on average across all seven monitored drip sites. Compared to the amount-weighted precipitation average δ18Oprecip value, the cave drip water δ18ODW values are evaporatively 18O enriched during infiltration through the soil/epikarst. As the monsoonal precipitation pulse fades and drip rates decrease, changes in the drip water chemistry (trace elements Mg/Ca and Sr/Ca, dissolved inorganic carbon δ13CDW, and δ18ODW values) indicate that prior calcite precipi- tation (PCP) drives the trace element and δ13CDW variability. The δ13Cc and δ18Oc values of farmed slide calcite are highly variable. However, high drip rate and lower cave air pCO2 during the monsoon combine to increase calcite precipitation rates. This causes speleothem records from these caves to be weighted toward annual monsoon conditions. Calcite isotope values from actively growing stalagmite tops support this finding. These results suggest that speleothems from these caves are sensitive to changes in monsoon precipitation amount, because it determines the duration of the monsoon drip water pulse, and therein, the extent of dry season PCP. Further, these data indicate that heterogeneity in the dolomitic limestone massif causes offsets between the carbon isotopes and trace metal concentrations between the caves, highlighting the need to normalize these datasets when chronology-stacking these proxies. 

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3. Coastal occupation and foraging during the last glacial maximum and early Holocene at Waterfall Bluff, eastern Pondoland, South Africa

   https://doi.org/10.1017/qua.2020.26  

   Fisher, Erich C.; Cawthra, Hayley C.; Esteban, Irene; Jerardino, Antonieta; Neumann, Frank H.; Oertle, Annette; Pargeter, Justin; Saktura, Rosaria B.; Szabó, Katherine; Winkler, Stephan; et al (September 2020, Quaternary Research)

   null (Ed.)

   Abstract Waterfall Bluff is a rock shelter in eastern Pondoland, South Africa, adjacent to a narrow continental shelf that limited coastline movements across glacial/interglacial cycles. The archaeological deposits are characterized by well-preserved stratigraphy, faunal, and botanical remains alongside abundant stone artifacts and other materials. A comprehensive dating protocol consisting of 5 optically stimulated luminescence ages and 51 accelerator mass spectrometry 14 C ages shows that the record of hunter-gatherer occupations at Waterfall Bluff persisted from the late Pleistocene to the Holocene, spanning the last glacial maximum and the transition from the Pleistocene to the Holocene. Here, we provide detailed descriptions about the sedimentary sequence, chronology, and characteristics of the archaeological deposits at Waterfall Bluff. Remains of marine mollusks and marine fish also show, for the first time, that coastal foraging was a component of some hunter-gatherer groups’ subsistence practices during glacial phases in the late Pleistocene. The presence of marine fish and shellfish further demonstrates that hunter-gatherers selectively targeted coastal resources from intertidal and estuarine habitats. Our results therefore underscore the idea that Pondoland's coastline remained a stable and predictable point on the landscape over the last glacial/interglacial transition being well positioned for hunter-gatherers to access resources from the nearby coastline, narrow continental shelf, and inland areas. 

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4. Determining the source of speleothem δ18O variability from in situ measurements of seasonal and inter-annual isotope trends in precipitation, cave drip water and modern calcite from sites in the Central Peruvian Andes

   Olson, E.J. (December 2022, American Geophysical Union Conference. Chicago, IL)

   In the past decade, Huagapo and Pacupahuain Caves in the Central Peruvian Andes have become sources of speleothem oxygen isotope (δ18O) paleoclimate records. These studies identify the South American Summer Monsoon (SASM) as the main climate system controlling δ18O variability. While this interpretation is verified through inter-proxy record comparisons on millennial scales, interpretation of the high-resolution variability within these records is limited by a lack of modern proxy calibration studies at these sites. Here we present results from a modern cave monitoring study undertaken to address the controls on the δ18O values of precipitation at these sites and how surface and in-cave processes affect the δ18O value of speleothem calcite. Speleothem calcite δ18O values reflect an integrated signal of atmospheric processes (e.g., rainout, Raleigh distillation, upstream moisture recycling, changes in moisture source), evaporation and mixing during infiltration in the soil and epikarst, and in-cave processes such as degassing and evaporation. In consideration of these factors, we compare isotope trends in precipitation, cave drip water and modern farmed calcite from the two cave sites. We find that precipitationδ18O values during peak monsoon activity (January -February) shows considerable inter-annual variation with averages of -16.7‰ for 2020, -18.5‰ for 2021 and -13.8‰ in 2022. We investigate the source of this variability in regional atmospheric circulation patterns using weather station data and back trajectories. The mean annual precipitation (MAP) from outside Huagapo Cave is δ18O = -15.5+/- 6‰, while seasonal samples of drip water δ18O = -14.5+/- 1‰, are offset from MAP possibly due to evaporation during infiltration. Cave drip waterδ18O has low variability over inter-annual and seasonal timescales indicating homogenization in the epikarst. Using geochemical and sensor data (e.g. cave relative humidity, temperature, and drip rate) as inputs for a karst based forward model, we simulate modern speleothem δ18O to quantitatively assess the combined effects of hydroclimate processes integration to the isotope record. 

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5. Stalagmite Records of Hydroclimate from the Peruvian Andes During the Last Deglaciation

   Olson, EL; Parmenter, D; Gillikin, D; Piccirillo, L; Forsyth, A; Litchfield, K; Verheyden, A; Edwards, L; Rodbell, D (December 2024, 2024 Fall Meeting, AGU)

   none (Ed.)

   Abstract The termination of the last glacial period is marked by the northward migration of the ITCZ and the weakening of the South American Summer Monsoon (SASM). The transition between the wetter glacial period and the more arid Holocene period across the South American continent is punctuated by several abrupt millennial-scale tropical hydroclimatic events. While the Northern Hemisphere temperature forcing of these millennial-scale events is generally accepted, recently, equatorial forcing mechanisms have been put forward. In particular, the dipole between northeastern Brazil and the western Andes of Peru is absent during Heinrich 1, with wet conditions recorded in both regions. To explain this anomalous atmospheric behavior, researchers have suggested changes in the ENSO and Walker circulation over South America and questioned whether the ‘amount effect’ relationship between δ18O and precipitation persists through time. To better resolve tropical hydroclimate changes over the last glacial termination, more robust paleoclimate proxies are needed. Here, we present a new paleo-precipitation reconstruction based on trace metal (Mg/Ca, Sr/Ca, and Ba/Ca) and isotope (δ18O and δ13C) speleothem records from Antipayarguna cave in the Peruvian Andes (3800 masl). Our records date from 2,600 to 4,700 and 7,700 to 19,000 years BP, with an average age resolution of 44 years. These records overlap the previously published speleothem records from nearby Pacupahuain and Huagapo caves. The Antipayarguna δ18O data are highly correlated with southern hemisphere summer insolation and the Huascaran ice core δ18O record. The Antipayarguna trace metal ratios and δ18O isotope values correlate well over most of the record, suggesting that the δ18O at our site reflects the amount of local precipitation. However, at the end of the Younger Dryas (11.5-10.3 ka) and Heinrich Stadial 1 (16.4-14.9 ka), there is a decoupling of these proxies. These anomalies may be due to changes in δ18O caused by shifts in moisture source region or precipitation condensation factors (e.g. convergence level or subcloud evaporation). Alternatively, this could be due to a change in trace metal sources. We explore potential causes for these brief decoupling events through comparison with other paleoclimate records. 

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