HR: 09:30h
AN: C51C-07    [Abstracts]
TI: A Mechanism for the High Rate of Sea-Ice Thinning in the Arctic Ocean
AU: * Bitz, C M
EM: bitz@apl.washington.edu
AF: University of Washington Polar Science Center, Box 355640, Seattle, WA 98195 United States
AU: Roe, G H
EM: gerard@ess.washington.edu
AF: University of Washington Earth Space Sciences, Box 351310, Seattle, WA 98195-1310 United States
AB: Submarine measurements of sea ice draft show that the ice has thinned in some parts of the Arctic Ocean at a remarkably high rate over the past few decades. The spatial pattern indicates that the thinning was a strong function of ice thickness, with the greatest thinning occurring where the ice was thickest initially. A similar relationship between sea ice thinning and the initial thickness is reproduced individually by three global climate models in response to increased levels of carbon dioxide in the models' atmosphere. All three models have weak trends in their surface winds and one model lacks ice dynamics altogether, implying that trends in the ice circulation are not necessary to produce a relatively high rate of thinning over the central Arctic or a thickness change that increases with the initial thickness. I will present a general theory to describe the thinning of sea ice subject to climate perturbations. Results from numerical models and theory alike indicate that the leading component of the thickness dependence of the thinning is likely due to the basic thermodynamics of sea ice. When perturbed, sea ice returns to its equilibrium thickness by adjusting its growth rate. The growth--thickness relationship is stabilizing and hence can be reckoned a negative feedback. The feedback is stronger for thinner ice, so thinner ice recovers more quickly from perturbations than thicker ice. I will discuss the implications of this feedback for recent observed changes in the ice thickness, including the reduced frequency of multiyear and ridged ice and increased frequency of firstyear ice.
DE: 4540 Ice mechanics and air/sea/ice exchange processes
DE: 1863 Snow and ice (1827)
DE: 1620 Climate dynamics (3309)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting