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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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REFINING THE AGE MODEL OF THE LAKE JUNIN (PERU) DRILL CORE BY CORRELATION TO REGIONAL CAVE STALAGMITES
Lake Junín, located in the uppermost Amazon Basin in central Peru, was drilled as part of the International Continental Drilling Program in 2015. A piston core with a composite length of ~95 m provides a continuous archive of upstream glacial activity spanning ~700,000 years. The age-depth model was established with 80 AMS 14C dates, 12 U-Th dated intervals of authigenic calcite, and 17 geomagnetic relative paleointensity tie points, and yields an age of 677±20 ka at 88 m. Four samples from near the base of the core reveal normal polarity paleomagnetic directions, consistent with an age younger than ~773 ka. The composite section comprises intervals of siliciclastic sediment intercalated with intervals dominated by authigenic calcite. The siliciclastic-rich intervals have a consistent signature, with relatively low concentrations of carbonate and organic carbon, and high values of bulk density, magnetic susceptibility and concentrations of elements derived from glacial erosion of the non-carbonate fraction of the regional bedrock. We find that tropical glaciers tracked changes in global ice volume and followed a clear ~100,000-year periodicity. Two caves, Huagapo and Pacupahuain, are located within 25 km of Lake Junín and provide a basis for testing and refining the age model of the Lake Junín drill core based on the high precision and accuracy of Uranium series dates for speleothems from these caves. The assumption here is that significant changes in regional ice volume will also be recorded in the 18O of cave drip water and thus in speleothems. Our initial target interval is the 9-8 marine isotope stage (MIS) boundary (~300 ka), which is recorded in the Junín drill core as an abrupt increase in the influx of glacigenic sediment, and in stalagmite 22-22 from Huagapo Cave as an abrupt 4.5‰ decrease in 18Ocalcite. The age of the onset of this transition in the Junín drill core is about 25 kyr older than that in Stal 22-22, and this difference is within the age model error envelope for the Junín drill core. Similar MIS boundaries provide the basis for adjustments in the Junín age model, which will improve the precision of correlation of this continuous record of tropical glaciation with paleoclimate archives in extra tropical regions.
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- PAR ID:
- 10518970
- 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-395566
