HR: 1340h
AN: PP23B-1344    [Abstracts]
TI: Simulation of Modern and Cretaceous δ¹⁸O With a Global Ocean-Atmosphere General Circulation Model
AU: * Zhou, J
EM: zotsing@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, United States
AU: Poulsen, C J
EM: poulsen@umich.edu
AF: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, United States
AU: Pollard, D
EM: pollard@essc.psu.edu
AF: Earth and Environmental Systems Institude, Pennsylvania State University, University Park, PA 16802, United States
AU: White, T S
EM: tswhite@essc.psu.edu
AF: Earth and Environmental Systems Institude, Pennsylvania State University, University Park, PA 16802, United States
AB: The δ¹⁸O content of marine carbonates has been the most prolific and powerful proxy for inferring past climate. However, this climate proxy requires knowledge of the ¹⁸O content of past marine waters. In the absence of such information, the ¹⁸O content of past waters is often assumed to be similar or systematically offset from modern. We test this assumption using an ocean-atmosphere general circulation model (GENESIS version 3.0 coupled to MOM2) to simulate modern and middle Cretaceous climates. Our model includes full water isotopic capabilities, including transport and fractionation in the atmospheric physics and passive transport in the ocean. The modern simulation of precipitation and marine δ¹⁸O in the model compares well with modern δ¹⁸O except in the Arctic Ocean where seawater δ¹⁸O is too low due to insufficient mixing with the global ocean. The Cretaceous zonal sea-surface δ¹⁸O predicted by the model is slightly (< 0.5‰) more depleted than modern in low latitudes and much heavier (by up to 8.5‰) in the Arctic Ocean. These differences are mainly due to the enhanced and unrealistic partitioning of light δ¹⁸O into the Arctic Ocean in the modern simulation. And the atmospheric transport of Cretaceous is similar to that of modern in our simulation, too. Our model results indicate that Cretaceous isotopic zonal gradients would have been similar to the modern unless isotopic partitioning between the global ocean and isolated basins were very different. Based on our model ƒÔδ¹⁸O, Cretaceous high latitude sea-surface temperature could be 4°C lower than estimates calculated using a global mean surface seawater δ¹⁸O. Our estimates reduce the equator- to-pole temperature gradient difference between model and proxy data without increasing model heat transport.
DE: 1600 GLOBAL CHANGE
DE: 1620 Climate dynamics (0429, 3309)
DE: 1622 Earth system modeling (1225)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4950 Paleoecology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting