HR: 17:45h
AN: PP54B-08    [Abstracts]
TI: Understanding Orbital Controls on Ice-Age Cycles
AU: * Poulsen, C J
EM: poulsen@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109 United States
AU: Lee, S
EM: shihyu@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109 United States
AU: Jacob, R L
EM: jacob@mcs.anl.gov
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AB: According to Milankovitch's theory of the ice ages, astronomically-forced high-latitude summer insolation variations controlled the initiation and growth of Northern Hemisphere ice sheets. Fluctuations in Earth's precession and obliquity both substantially influence high-latitude insolation, and should be preserved as variability in the ice-volume record. Yet, while Pleistocene records of benthic δ¹⁸O possess large spectral power in the obliquity band, they show only feeble power in the precessional band. To explain the missing precessional signal, we have conducted a series of coupled ocean-atmosphere GCM experiments that test the high-latitude climate sensitivity to orbital parameters. In agreement with the paleoclimate record, our model demonstrates a much larger response to obliquity variations than to precessional variations. For example, the mean-annual Northern Hemisphere sea-ice extent and snowfall rate response to a reduction in axial tilt is three times greater than that to a 180° change in precession (from a Northern Hemisphere warm to cold summer orbit). The difference in the high-latitude response to orbital parameters is primarily linked to moisture transport through transient eddy activity. A reduction in obliquity enhances the summer meridional insolation gradient, increasing poleward moisture transport through transient eddies by nearly 25%. In contrast, precessional changes lead to a slight reduction in transient eddy moisture transport. Our model results suggest that a revision to Milankovitch theory may be in order.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1626 Global climate models (3337, 4928)
DE: 4910 Astronomical forcing
DE: 4946 Milankovitch theory
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005