HR: 17:30h
AN: PP34B-07    [Abstracts]
TI: Climate Models Suggest No Prominent Role of the Panamanian Gateway Closure in Northern Hemisphere Glaciation
AU: * Schulz, M
EM: mschulz@palmod.uni-bremen.de
AF: Research Center Ocean Margins (RCOM) and Department of Geosciences, University of Bremen, PO Box 330440, Bremen, 28334 Germany
AU: Prange, M
EM: mprange@palmod.uni-bremen.de
AF: Research Center Ocean Margins (RCOM) and Department of Geosciences, University of Bremen, PO Box 330440, Bremen, 28334 Germany
AB: The most significant climate transition of the Pliocene was the pronounced intensification of Northern Hemisphere glaciation, which culminated in a synchronous ice-sheet development between Greenland, Eurasia and North America around 2.7 million years ago. Various hypotheses have been proposed to explain the sudden appearance of major ice sheets in the Northern Hemisphere. One hypothesis, which has received much attention, relies on the combined effects of the closure of the Panamanian Gateway and favorable orbital forcing. Utilizing climate models of different complexity, we test the hypothesis that the Pliocene closure of the Panamanian Gateway was a necessary precondition for orbitally triggered Northern Hemisphere glaciation. The first model is an Earth-system model of intermediate complexity (ECBilt-CLIO) while the second is a comprehensive climate model (CCSM 2.01). We conduct a series of sensitivity experiments with both models in order to analyze the isolated and combined effects of Panama closure and orbital forcing on perennial snow cover. In both models, orbital forcing efficiently controls the extension of the snow cover in the Northern Hemisphere. The closure of the Panamanian Gateway leads to an intensification of the thermohaline circulation in the Atlantic Ocean in both models. South of Iceland the associated increase in meridional heat and salt transports raise annual-mean sea-surface temperature by approx. 1-2 K and sea-surface salinity by approx. 0.5 psu. Both changes are in good agreement with recent paleoceanographic reconstructions at ODP Site 984 for the time of the Panama closure [Bartoli et al., 2005; EPSL]. Although the warmer surface layer in the North Atlantic intensifies snowfall on the adjacent continents, the effect on perennial snow cover remains negligible due to enhanced summer melting. Accordingly, the model experiments do not suggest that the closure of the Panamanian Gateway intensifies orbitally forced glaciation in high northern latitudes.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4928 Global climate models (1626, 3337)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005