Ice-sheet numerical modeling and marine geophysical measurements of glacier-derived sedimentation on the Eurasian Arctic continental margins

摘要

Long-range side-scan sonar images of the Barents Sea continental margin have been analyzed in conjunction with results from previous geophysical investigations to determine a qualitative model for sedimentation over the Bear Island and Storfjorden trough mouth fans. These data indicate that gravity-driven debris flows are major processes in the downslope transport of glacial material, delivered to the shelf break when ice sheets advanced across the continental shelf. During late Weichselian time, 4000 km3 of sediments were deposited over the Bear Island fan (280 000 km2) while 700 km3 of sediments were deposited over the Storfjorden fan (40 000 km2). A numerical ice-sheet model, including sediment deformation and transport beneath ice streams, reconstructs the glacial conditions required to transport large volumes of sediment to the late Weichselian Eurasian continental margin. Model results indicate that glaciation of the Eurasian High Arctic occurred after 28 ka, and that ice streams within bathymetric troughs were active by ca. 25 ka. The maximum ice-sheet thickness over the Barents Sea was about 1400 m; there was a secondary dome <1200 m thick over the Kara Sea. Ice extended to the shelf break along the western Barents Sea and Arctic Ocean margins. Ice-sheet decay affected the marine portions of the ice sheet after 15 ka, leaving a northern ice mass between Svalbard and Franz Josef Land that decayed after 13 ka. Ice streams draining ice west and north from the Barents-Kara Sea existed in major bathymetric troughs. Model results predict that ice streams transported sediments to the margin from 27 to 13 ka. Sediment delivery to the margins was generally very high during that time. At 15 ka, the sedimentation rate over the 200-km-wide mouth of the Bear Island trough was 4 cm yr–1 (0.13 cm yr–1 averaged over the fan); the rate was 6 cm yr–1 (equivalent to 0.6 cm yr–1 over the fan) over the Storfjorden trough mouth. The modeled sediment volume at the continental margin of the Bear Island and Storfjorden troughs agrees well with the volumes of late Weichselian sediment inferred from seismic records from these large prograding submarine fans. Sensitivity experiments show that adjustments to model environmental inputs do not significantly affect the results.