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For the past few decades, many researchers have sought to understand how tropical hydroclimate responds to climate change via lakes, marine sediments, and speleothems records. Speleothem δ18O records throughout South America have shown that regional rainfall responds to Northern Hemisphere forcing on the millennial scale. Areas under the influence of the South Atlantic Convergence Zone (SACZ) have also shown a close relationship with local insolation on longer timescales. However, apart from the Cruz et al. (2007) record in Southern Brazil, long-term speleothem records throughout the continent have relied primarily on stable oxygen isotopes and are therefore limited to describing large-scale regional variability in rainfall. As such, many areas in South America still lack long-term records of local hydroclimate, which is critical to understanding how different components of the monsoon system respond to orbital and millennial-scale climate change. One proxy that has gained more attention in recent years is trace metal-to-calcium ratios (TM/Ca). Sr, Mg, and Ba to Ca ratios in speleothems are known in certain situations to respond to the degree of Prior Calcite Precipitation (PCP) above a drip site, a phenomenon directly tied to local aridity. In this study, we have obtained high-resolution TM/Ca measurements to pair with stable isotopes from samples spanning 23 to 66 ka from Huagapo Cave in the Peruvian Andes (11.27°S; 75.79°W). TM/Ca ratios in these samples are strongly correlated (R2>0.89), making them suitable for use as PCP proxies. We see that decreases in δ18O during Heinrich events are accompanied by a drop in TM/Ca. The period defined by the MIS 4/3 transition is accompanied by a simultaneous increase in TM/Ca and δ18O. TM/Ca and δ18O negatively correlate with local insolation for the entire record. Interestingly, the Paraíso Cave record from the Amazon Basin shows no correlation between regional or local hydroclimate and insolation during the last glacial period. The discrepancy between the two records and the close relationship between TM/Ca, δ18O, and local insolation in Huagapo samples, may call for a revised interpretation of Andes speleothem δ18O variability, which was originally thought to reflect rainout over the Amazon Basin.
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MIDDLE PLEISTOCENE HYDROCLIMATE CHANGES IN THE TROPICAL ANDES INFERRED FROM CARBON AND OXYGEN ISOTOPE RECORDS OF SPELEOTHEMS FROM HUAGAPO CAVE, PERU
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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- PAR ID:
- 10518973
- Publisher / Repository:
- Geologic Society of America
- Date Published:
- Format(s):
- Medium: X
- Location:
- Pittsburgh PA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1130/abs/2023AM-394169
