Abstract

The southern Yermak Plateau (northwest of Spitsbergen) was investigated with 11-12 kHz sidescan sonar and 3.5 kHz profiler to test whether thick Pleistocene ice streams ever calved into the Arctic Ocean and/or whether a continuous Arctic ice sheet existed. In either case, the ice would have grounded on the plateau crest on its way out of the Arctic. Several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m, perhaps recording the deepest iceberg keels known. The plateau crest (510-530 m) is nearly bare of plowmarks, perhaps because of beveling by an ice rise formed of grounding shelf ice. This implies continuous, 400-600-m-thick grounded ice, consistent with but not proving the postulated existence of an Arctic ice sheet. Most plowmarks are probably late Pleistocene products of the calving of Barents-Kara ice sheets into the Arctic Ocean. Plowmarks in 450-850-m-deep water require unusually deep ice-sheet grounding lines (e.g., Svyataya Anna Trough) and/or drat-increasing capsizing events, even if sea levels were 100-50 m lower than today. At water depths of 800 to 1800 m, the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau.

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