NEW SIDESCAN SONAR EVIDENCE FOR THE WESTWARD FLOW OF ICE ACROSS THE ALASKA MARGIN, ARCTIC OCEAN

Recent post-processing of 12kHz sidescan sonar data collected during the 1999 Science Ice Exercises (SCICEX) cruise shows strong evidence for the westward flow of ice across the Alaska Margin in the Arctic Ocean. Linear alignments of submarine glacial flutes measuring up to 10s of meters deep, >10km in length and arrayed in fields several kilometers across are prominent on the seafloor south of the continental shelf/slope break. The orientation of these flutes trends parallel to the Alaska Margin at 72ºN between –158º and –142º. In some locations, it is possible to distinguish flutes with slightly differing orientations in the same geographic area, though no obvious overprinting relationships are visible. There are also several regions that have been deeply scoured by randomly oriented furrows typical of iceberg keel tracks. These iceberg-impacted areas tend to cluster in the shallowest water depths at the southern margin of the study area.

Though it is not possible to determine from the bi-directional linear flute features observed in the sidescan data the true paleo-flow direction of the ice that formed them, there are two previous studies that predict westward flow of ice in this area. Work by Polyak et al., [2001] on the proximal Chukchi Plateau and Northwind Ridge indicates ice flow directions trending northwest, while sites due landward of the Chukchi Plateau show ice scours with a northeast orientation. Polyak et al., [2001] hypothesize that ice streams flowed west from the Canadian Arctic Archipelago (CAA) across the Alaska Margin and then were deflected to the north by a northeast trending Chukchi Ice Sheet or a steep continental shelf. Grosswald and Hughes [1999] predict that ice streams from the CAA would be deflected west across the Alaska Margin by a central pan-Arctic ice mass. Our data from the Alaska Margin are consistent with both of these predictions and also match the inferred paleo-flow direction of the Beaufort Gyre. Additional data will be necessary to determine the true cause of westward ice flow in the region.