HR: 09:30h
AN: U51B-07    [Abstracts]
TI: Synchronization of Glacial-Interglacial SST changes in the Tropical Oceans: Evidence for Amplification of Climate Sensitivity by Carbon Dioxide Over the Past 2.7 Ma
AU: * Herbert, T D
EM: Timothy_Herbert@brown.edu
AF: Brown University, Dept. of Geological Sciences Box 1846, Providence, RI 02912, United States
AU: Cleaveland, L
EM: Laura_Cleaveland@brown.edu
AF: Brown University, Dept. of Geological Sciences Box 1846, Providence, RI 02912, United States
AU: Liu, Z
EM: zhonghui.liu@yale.edu
AF: Yale University, Dept. of Geology and Geophysics, New Haven, CT 06520-8109, United States
AU: Lawrence, K T
EM: lawrenck@Lafayette.edu
AF: Lafayette College, Dept. of Geology and Environmental Sciences, Easton, PA 18042, United States
AB: Understanding the links between tropical sea surface temperatures (SST) and changes in high latitude climate across ice age cycles has challenged paleoclimatologists for some time. On the one hand, the tropical oceans should be shielded from processes that produce large temperature sensitivity in the high latitudes (ice-albedo feedback, sea-ice feedback, steering of wind fields by ice sheets, etc.). However, the high latitudes exert an influence on tropical ocean temperatures through the thermocline, and, perhaps via the atmosphere by modulating the CO₂ greenhouse effect. The tropics, in turn could provide important feedbacks to glacial cycles via their influence on water vapor and clouds. Work with recently developed SST proxies (Mg/Ca, alkenone U^k'₃₇) has proven that substantial sensitivity exists in tropical SST on a glacial-interglacial timescale over the course of the last ~ 1Ma. Over the extent of the EPICA ice core record, this sensitivity is coherent with glacial-interglacial variations in CO₂. In this study, we have extended the tropical SST record to the mid-Pliocene (3.5 Ma) in tropical locations in the Atlantic, Indian and Pacific oceans. We use the alkenone unsaturation index, recorded at ~ 3kyr resolution at each of three sites, in conjunction with benthic foraminiferal δ¹⁸O measured at the same sites, which synchronizes the records and allows for a direct comparison of tropical SST to ice volume changes. We find that all three tropical sites show long-term cooling over the last three million years, although the rate of cooling is the steepest in the eastern equatorial Pacific. Glacial-interglacial SST variation is strikingly similar in the three tropical basins after 2.7 Ma, with a succession of 41 kyr (obliquity) cycles persisting up to the transition to 100 kyr cycles at about 800 ka. Prior to 2.7 Ma, temperatures at the three sites behave idiosyncratically on the orbital timescale. A further intriguing observation is the existence of coherent 300-500 kyr cycles in SST in all three basins (also observed in Mg/Ca data) that may not be related to orbital forcing. We evaluate and reject the case that the tropical SST cycles originate dominantly from upwelling/thermocline- driven processes, and argue instead that the SST data suggest that a coherent, substantial CO₂-glaciation feedback began at about 2.7 Ma, synchronizing to first order the tropical SST variations on orbital timescales in late Pliocene and all of Pleistocene time. The key event at 2.7 Ma, therefore was the phase locking of CO2 and ice/sea ice feedbacks to orbital forcing. Furthermore, the large tropical SST memory observed (the 300-500 kyr wavelength) argues for the importance of a long response time element in the climate system, most likely ocean biogeochemical cycles and CO₂, in modulating tropical SST on supra-orbital timescales. Prior to 2.7 Ma, the combination of glacial and CO₂ feedbacks may have been much weaker, diminishing the similarity of tropical SST patterns between the different ocean basins, and lessening their sensitivity to high latitude processes.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1055 Organic and biogenic geochemistry
DE: 4910 Astronomical forcing
DE: 4954 Sea surface temperature
SC: Union [U]
MN: 2007 Fall Meeting