Variations in the Age of Arctic Sea-ice and Summer Sea-ice Extent
Ignatius Rigor1, 2, John M. Wallace2
1Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington
2Department of Atmospheric Sciences, University of Washington, Seattle, Washington
|Read the full paper (PDF): Geophys. Res. Lett., v. 31, doi: 10.1029/2004GL019492, 2004.|
Three of the past six summers have exhibited record low sea-ice extent on the Arctic Ocean. These minima 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.
The red dots shows the current location of buoys used to estimate the age of sea ice. The areas of older, thicker ice are shown in white, while younger, thinner sea ice is shown as darker shades of blue.
This animation of the age of sea ice shows:
1.) A large Beaufort Gyre which covers most of the Arctic Ocean during the 1980s, and a transpolar drift stream shifted towards the Eurasian Arctic. Older, thicker sea ice (white ice) covers about 80% of the Arctic Ocean up to 1988. The date is shown in the upper left corner.
2.) With the step to high-AO conditions in 1989, the Beaufort Gyre shrinks and is confined to the corner between Alaska and Canada. The Transpolar Drift Stream now sweeps across most of the Arctic Ocean, carrying most of the older, thicker sea ice out of the Arctic Ocean through Fram Strait (lower right). By 1990, only about 30% of the Arctic Ocean is covered by older thicker sea ice.
3.) During the high-AO years that follow (1991 and on), this younger thinner sea ice is shown to recirculated back to the Alaskan coast where extensive open water has been observed during summer.
The age of sea ice drifting towards the coast explains over 50% of the variance in summer sea ice extent (compared to less than 15% of the variance explained by the seasonal redistribution of sea ice, and advection of heat by summer winds).
Rigor was funded by a fellowship from the Applied Physics Laboratory, University of Washington, by NOAA Grant NA17RJ1232, and ONR Grant N00014-98-1-0698. Wallace was funded by the National Science Foundation under grant ATM 0318675. This publication was partially funded by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement No. NA17RJ1232, Contribution #1054.
References and notes:
 The buoy data was obtained from the International Arctic Buoy Programme.
 Comiso, J. C. (1995), SSM/I ice concentrations using the Bootstrap algorithm, NASA Rep., 1380. This analysis has been updated.