HR: 16:00h
AN: C44A-01    [Abstracts]
TI: Insolation driven ice sheet changes in the early Pleistocene
AU: * Scherer, R
EM: reed@geol.niu.edu
AF: Northern Illinois University, Department of Geology & Environmental Geosciences, DeKalb, IL 60115, United States
AB: Precisely dated Antarctic nearshore and offshore proxy (not direct) records of ocean surface changes imply ice sheet changes that appear to be directly and profoundly influenced by precession paced high latitude insolation. Stratigraphic records from the southwestern Ross Sea (Cape Roberts Project and ANDRILL) can be directly correlated with offshore records (ODP) of Marine Isotope Stage 31 (MIS-31) by the position of the base of the Jaramillo subchron (C1r.1n), which is identified based on biostratigraphic and isotopic dating. Microfossil data show that the southern Ross Sea was ca. 4 degrees warmer than today, and that the polar front shifted well south of its current position. Coastal sea ice was largely absent during the summer and open ocean surface waters were stratified with a shallow, low salinity mixed layer. MIS-31 was characterized by some of the highest high-latitude insolation values of the last 5 million years, with high obliquity, eccentricity, and precession, and perihelion in the austral summer early in the interglacial, at 1.08 Ma, followed by a northern hemisphere peak at 1.07Ma. These parameters drove a model-predicted +20 m eustatic sea-level rise during MIS-31 [Raymo et al., 2006], the highest of the late Pliocene/early Pleistocene and reflecting significant retreat or collapse of the Greenland Ice Sheet plus some combination of the West Antarctic Ice Sheet and marginal East Antarctic ice. Our findings appear to corroborate the hypothesis of Raymo et al. [2006] that the interhemispheric antiphased relationship of the precession cycle typically attenuates a potentially significant ice volume signal in the deep sea oxygen isotope record. MIS-31 is the "exception that proves the rule" in that the unusually strong insolation in the Antarctic (at 1.08 Ma) triggered stronger than usual melting, which was quickly followed by intense melting in Greenland (at 1.07 Ma). In this case, Greenland melting occurred prior to full regrowth of Antarctic ice. The implication of these findings and interpretations is that the ice sheets may be more susceptible to high insolation driven retreat than has been widely recognized.
DE: 0726 Ice sheets
DE: 4934 Insolation forcing
DE: 4936 Interglacial
DE: 4954 Sea surface temperature
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: 2007 Fall Meeting