HR: 10:35h
AN: C52A-02 INVITED     [Abstracts]
TI: Explaining the Recent Decreases in Sea Ice on the Arctic Ocean
AU: * Rigor, I G
EM: ignatius@apl.washington.edu
AF: Polar Science Center, Applied Physics Laboratory University of Washington 1013 NE 40th Street, Seattle, WA 98105
AU: * Rigor, I G
EM: ignatius@apl.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195
AU: Wallace, J M
AF: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195
AB: Three of the past six summers have exhibited record low sea-ice extent on the Arctic Ocean, and this summer appears to be on pace to set a new record minimum. Simultaneous decreases in sea ice thickness have also been observed (Rothrock, et al. 1999). Taken together, these observations imply a precipitous decline in the total volume of sea ice on the Arctic Ocean. Is this decline due to changes in the advection of heat into the Arctic, or due to a simple change in winds and the drift of sea ice on the Arctic Ocean? Rigor, et al. (2002) showed that the winter wind anomalies associated with the high-index AO conditions increases the advection of ice away from the Eurasian and Alaskan coasts. This advection increases the production of thin ice in the flaw leads along the coast during winter, and preconditions the sea-ice to be more prone to melt during the following spring and summer. During summer, low-index AO conditions favor southeasterly wind anomalies which increase the advection of ice away from the Alaskan coast and increase the advection of warm air onto the ocean, both of which act to decrease the amount of ice in the Beaufort and Chukchi seas. However, the impact of the summer AO on sea-ice extent appears to be preconditioned by the state of the AO during the previous winter, and in recent years the correlations between the summer AO-index and sea-ice extent are not as strong as they were in prior years. For example, during the summers of 2002 and 2003, the summer AO was in a high-index phase, which favors above normal ice concentrations along the Alaskan coast, and yet record minima were observed during both years. We hypothesize that the minima in Arctic sea ice extent may have been dynamically induced by changes in the surface winds. Based on results of a simple model that keeps track of the age of ice as it moves about on the Arctic Ocean, we argue that the areal coverage of thick multi-year ice decreased precipitously during 1989-1990 when the Arctic Oscillation was in an extreme "high index" state, and has remained low since that time. Under these conditions, younger, thinner ice anomalies recirculate back to the Alaskan coast more quickly, decreasing the time that new ice has to ridge and thicken before returning for another melt season. During the 2002 and 2003 summers this anomalously younger, thinner ice was advected into Alaskan coastal waters where extensive melting was observed, even though temperatures were locally colder than normal. The age of sea-ice explains more than half of the variance in summer sea-ice extent.
UR: http://iabp.apl.washington.edu/IceAge&Extent/
DE: 9315 Arctic region
DE: 4207 Arctic and Antarctic oceanography
DE: 4215 Climate and interannual variability (3309)
DE: 4540 Ice mechanics and air/sea/ice exchange processes
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting