HR: 10:20h
AN: PP52B-01 INVITED     [Abstracts]
TI: Rethinking The Cenozoic Record of Ice Volume: A Modeling Perspective on the Relative Contributions of Southern and Northern Hemispheres
AU: * DeConto, R M
EM: deconto@geo.umass.edu
AF: Department of Geosciences, University of Massachusetts, Amherst, MA 01003 United States
AU: Pollard, D
EM: pollard@essc.psu.edu
AF: Earth System Science Center, Pennsylvania State University, University Park, PA 16802 United States
AB: The sudden growth of a continental-scale East Antarctic Ice Sheet (EAIS) in the earliest Oligocene (~34 Ma) has long been thought to represent the first major glaciation of the Cenozoic. The timing of the first significant ice on Greenland remains equivocal, however, the Northern Hemisphere is usually assumed to have remained mostly ice-free until the onset of the major 40-kyr glacial cycles in the Pliocene (~2.7 Ma). Recent numerical modeling studies using coupled GCM-ice sheet models have successfully simulated the sudden continental-scale glaciation of Antarctica in the earliest Oligocene (Oi-1), in response to a combination of decreasing atmospheric CO₂ and orbital and/or tectonic forcing. However, the simulated Antarctic ice sheet, roughly equivalent to the modern EAIS, is 2-3 times too small to account for the ice volume implied by recent paired isotopic and Mg/Ca analyses of the Oi-1 event. Similar model-data inconsistencies apply to other isotopic shifts in the Paleogene and early Neogene (Mi events), adding uncertainty to isotope-Mg/Ca reconstructions of ice volume and/or assumptions regarding the isotopic composition of ancient ice sheets. Because the accommodation space for grounded ice in the Southern Hemisphere is limited, the isotope-Mg/Ca data can also be interpreted to imply significant ice in the Northern Hemisphere. Here, we apply a coupled GCM-ice sheet model to test the possibility of Northern Hemispheric glaciation in the Paleogene and early Neogene. Our results are discussed in the context of the envelope of forcing required for Northern Hemispheric ice in the early Cenozoic and the possibility that the onset of Antarctic ice sheets preconditioned the climate system for episodic bipolar glaciation.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4928 Global climate models (1626, 3337)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005