A Tropical Speleothem Record of Glacial Inception, the South American Summer Monsoon from 125 to 115 ka
Abstract
Paleoclimate studies of Earth's transitions from glacial to interglacial states over the past several hundred thousand years have focused on glacial terminations, in particular Termination I. There are comparatively few records of the other transition between climate states - glacial inception. We present a high-resolution, well-dated speleothem record of changes in the South American Summer Monsoon from 125 to 115 ka, a period covering the transition from the penultimate interglacial to the last glacial period. Sample P10-H1 is from Huagapo Cave (11.27°S; 75.79°W) ~3,850 meters above sea level (masl) in the central Peruvian Andes. The sample grew from about 125.2 to 115.2 ka. The oxygen isotope time series shows that the SASM was relatively weak during MIS 5.5, particularly during the last 2000 years of the interglacial period. The SASM strengthened rapidly, mainly in two approximately equal steps, at 121 ka and at 117 ka. The P10-H1 time series follows January insolation at 10°S, though the response of the SASM to insolation is clearly non-linear. Maximum monsoon intensity is reached at close to the maximum in summer insolation at 10°S. Our record of SASM changes over the transition from MIS 5.5 to 5.4 is mirrored to a remarkable degree by observed changes in the East Asian Monsoon as recorded in stalagmites from Dongge Cave in China (Kelly et al., 2006). The transition from peak interglacial conditions at the end of MIS 5.5 to glacial conditions at MIS 5.4 occurred in 4000 years or less in tropical speleothems records. The precise temporal relationship between marine δ18O records, and therefore sea level, and the speleothem δ18O records is not simple to unravel. Ice core atmospheric oxygen δ18O data provide method of connecting the marine record to the ice cores and hence to the speleothems. The minimum in δ18O atm in the NGRIP ice core is at 116 ka, just at the transition from GS25 to GIS25 (Landais et al., 2006). Because the primary control on δ18Oatm is the isotopic composition of seawater, the location of the δ18Oatm maximum in NGRIP indicates that the maximum in the marine δ18O values at MIS 5.4 occurs in conjunction with the first minimum in P10-H1 and the maximum in Hulu H3, at ~116 ka. Northern Hemisphere ice volume was probably also between 40% and 50% of the LGM maximum at the time of MIS 5.4. The speleothem records suggest that this amount of ice grew in less than 4000 y.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP42A..01B
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1616 GLOBAL CHANGE / Climate variability;
- 1620 GLOBAL CHANGE / Climate dynamics