HR: 09:15h
AN: C21C-06    [Abstracts]
TI: Spatial and temporal variability of Arctic sea-ice draft, 1975-2005
AU: * Wensnahan, M R
EM: thinice@apl.washington.edu
AF: Applied Physics Lab, University of Washington, Seattle, WA 98117, United States
AU: Moritz, R E
EM: dickm@apl.washington.edu
AF: Applied Physics Lab, University of Washington, Seattle, WA 98117, United States
AU: Rothrock, D A
EM: rothrock@apl.washington.edu
AF: Applied Physics Lab, University of Washington, Seattle, WA 98117, United States
AU: Percival, D B
EM: dbp@apl.washington.edu
AF: Applied Physics Lab, University of Washington, Seattle, WA 98117, United States
AB: Sea-ice draft measurements made by upward looking sonars are used to estimate the mean drafts of nominal 50 km horizontal segments acquired on 34 U.S. Navy submarine cruises from 1975 to 2000. The cruises are distributed equally in spring and autumn, and the 2203 mean drafts in the data release area provide coverage of approximately half of the Arctic Ocean. The spatial and temporal variability is modeled by multiple regression as a sum of contributions by a time-average spatial field, a mean annual cycle that is independent of position, a long-term time variation, and a residual. Taken together, the spatial, annual and long-term components explain 79% of the total variance in the data. The overall mean is 2.97 m. The amplitude of the annual cycle is 1.06 m. The time-independent spatial map has a minimum draft of 2.2 m near Alaska and a maximum of 4 m at the edge of the data release area 200 miles north of Ellesmere Island. The long-term variation exhibits thinning ice with a peak draft of 3.42 m in 1980 and a minimum draft of 2.29 m in 2000, a decrease of 1.13 m. The maximum rate of thinning is -0.08 m/yr in 1990. The long-term variation nearly levels off at -0.007 m/yr by the end of the record in 2000. Similar multiple regression analyses are performed on a smaller region centered on the North Pole (NP), where the coverage provided by submarine-mounted sonars is denser than average. The annual cycle and long-term variation for this NP region are similar to corresponding parameters estimated for the entire data release area. However there is little coherent spatial variability in NP and the total variance explained by the model is reduced to 65%. Some of the unexplained variance is related to substantial variability in the summer ice draft. Ice draft measurements from sonars moored at the North Pole Environmental Observatory are used to extend coverage in the NP region to spring 2005. The extended data support the "leveling off" of the long term variation, seen at the end of the submarine-only analysis that ends in 2000. The extended data set does not indicate a continuation of thinning in the NP region from 2000 to 2005.
DE: 0750 Sea ice (4540)
DE: 1621 Cryospheric change (0776)
DE: 9315 Arctic region (0718, 4207)
SC: Cryosphere [C]
MN: 2007 Fall Meeting