Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Was Sea Ice Quite Thin in the 1990's? Yes
D. Andrew Rothrock1
1Polar Science Center - Applied Physics Laboratory, University of Washington, Seattle, WA, 98105, USA, Phone 206-685-2262, Fax 206-616-3142, rothrock@apl.washington.edu
Submarine observations of sea ice draft from 1987 to 1996 show a decrease of about one meter over the eleven year span. These data are digitally recorded by U.S. Navy submarines in a central (essentially the deep-water) half of the Arctic Ocean. All numbers here pertain to ice draft, which is about 0.89 of ice thickness. A comparison of average drafts over entire cruises with those from our sea ice model shows good agreement in the temporal change, with an rms discrepancy of 0.3 m. The spatial variation within cruises shows greater rms discrepancy -- about 0.7 m, with modeled ice thicker than observed ice in the Beaufort Sea area and thinner near the North Pole.
We have reviewed papers in the literature of modeled interannual variations in thickness or ice volume. All models agree that thickness decreased by between 0.6 and 0.8 m from 1987 to 1996, but they tend to differ in their simulations of the 1950's to 1970's. Our model shows this decline in thickness in the 1990's over most of the Arctic Ocean; there is almost no offsetting increase near the Canadian Archipelago.
A regression analysis of these submarine draft data shows that about three quarters of the variance can be explained by three variants: an annual cycle with an amplitude of 1.1 m, a linear spatial gradient from the East Siberian Sea to Greenland of 0.8 m per thousand kilometers, and a downward trend of 0.07 m per year. This is perhaps the most satisfying method for isolating and estimating a trend from data of different cruise tracks in different seasons and different years.
Historical submarine ice draft data can shed light on the records back to 1958. We show an inventory of all the submarine cruises for which draft data exist and are being processed and declassified.
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