Sensitivity of the South American Summer Monsoon to high latitude temperature changes during the Last Glacial period
Abstract
The climate of the Last Glacial period (10-110 kya) is characterized by rapid, millennial-scale climate fluctuations termed Dansgaard/Oeschger (D/O) and Heinrich (H) events. D/O and Heinrich events have been recognized in many terrestrial and marine records, particularly from the Northern Hemisphere. However, the presence of D/O cycles in the Southern Hemisphere and their relationship to Southern Hemisphere monsoons has not been established. We present results from a speleothem-derived proxy of the South American Summer Monsoon (SASM) from 16-50 kya that clearly demonstrate the occurrence of D/O cycles and Heinrich events. Stalagmite P09-PH2 was recently collected from Pacupahuain Cave in the central Peruvian Altiplano (12°S, 76°W, ~3800m elevation). Chronologies were determined by U-Th dating techniques and seventeen 230Th dates, all in stratigraphic order, have analytical errors < 0.4%. Stable oxygen isotope ratios (δ18O) were measured on 834 micromilled samples taken along the growth axis, yielding an average resolution of 30 years. Oxygen isotopic values of stalagmite P09-PH2 range from -14% to -17.5%. The long-term record of δ18O is characterized by a series of high amplitude, millennial-scale events. Rapid enrichments of up to 2.5% occur over a century or less while more gradual depletions occur over a few centuries to millennia. Comparing the millennial-scale variability in the Pacupahuain Cave record to the isotopic fluctuations from Greenland shows that all D/O cycles, with the exception of D/O event 3, are also found our record of SASM intensity. Abrupt oxygen isotopic enrichments in Greenland, which characterize the onset of the D/O events, are positively correlated with millennial-scale isotopic enrichments in P09-PH2. This correlation indicates that warm events at high, northern latitudes are related to intervals of decreased SASM intensity. Heinrich events H1 through H5 are also identified in our reconstruction by highly depleted values in speleothem δ18O, providing further support for increased SASM intensity during northern hemisphere cold intervals. The manifestation of D/O cycles and Heinrich events in SASM variability is anti-phased with Northern Hemisphere monsoon precipitation reconstructions over the Last Glacial period. We interpret this interhemispheric anti-phasing to be the result of latitudinal shifts of the Intertropical Convergence Zone (ITCZ) and specifically ITCZ migration away from the hemisphere with high latitude cooling. Our results also show previously unrecognized millennial-scale climate events that result from the interplay between rapid Antarctic warming and Greenland stadial conditions. We use the signature of the high latitude temperature changes in P09-PH2 to establish the timing and duration Heinrich events H2 through H5.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP31C1888K
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 9360 GEOGRAPHIC LOCATION / South America