Heinrich-like events in the Southeast Pacific: abrupt climate change during the last interglacial

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American Geophysical Union
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EOS Transactions

Many previous studies of orbital and sub-orbital scale climate changes in the marine record during the last glacial-interglacial transition have focused on evidence from the Northern Hemisphere. While solar insolation at 65°N evidently plays a primary role in pacing orbital changes, determining the mechanism(s) transferring climatic changes around the globe at orbital and sub-orbital time scales also requires records from the mid and high southern latitudes (Pahnke et al., 2003). Here we present such a record from ODP Leg 202, Site 1234 located 65 km off the Chilean margin (36°13.153'S, 73°40.902'W). With a high sedimentation rate of ~80 cm/kyr, the core site represents an opportunity to examine Marine Isotope Stage 5 (MIS 5), the last interglacial, in high resolution. Using quantifications of ice rafted debris (IRD), foraminiferal abundances, N. pachyderma (sinistral) abundance and oxygen isotopes from planktonic and benthic foraminifera, the present study provides an 80 kyr record of climate change. We resolved MIS 5 in sufficient detail to observe the MIS 5/6 boundary, sub-stages MIS 5a through MIS 5e, and millennial-scale variability during the transition from the last interglacial into the last glacial era. Comparison of our records of MIS 5 with records from the North Atlantic (Oppo et al., 2001) demonstrates that orbital-scale warming in the two hemispheres appears to be approximately synchronous, though from our data it is not possible to infer a precise phase relationship in order to constrain a synchronization mechanism. At shorter time scales, a comparison of our records during the last interglacial with records from the North Atlantic (McManus et al., 1998) shows that episodes of ice rafting at our site, associated with changes in foraminiferal abundances and oxygen isotope content, are similar to, and correlated with, evidence of small-scale Heinrich events in the North Atlantic. This suggests that the expansion and retreat of Andean glaciers, as well as hydrographic variations near the Chilean margin, occurred in concert with abrupt changes in the Northern Hemisphere. While previous studies have found widespread global responses related to North Atlantic Heinrich events, this is the first record to show direct evidence of analogous climate changes in the Southeast Pacific. The existence of these events, in phase with those in the North Atlantic, provides constraints on the mechanisms forcing abrupt climate changes.