Glaciogenic Bedforms on the Chukchi Borderland, Morris Jesup Rise and Yermak Plateau: Three Prolongations of the Arctic Ocean Continental Margin

The US Coast Gard Cutter Healy and Swedish icebreaker Oden have collected multibeam bathymetry and subbottom profiles from the Chukchi Borderland, extending out from the continental shelf of northern Alaska, the Morris Jesup Rise north of Greenland and the Yermak Plateau protruding out from the northwestern Svalbard continental margin. The collected data show glaciogenic bedforms in the form of mega scale glacial lineations, flutings, iceberg scours, morainic ridges and conspicuous erosional channels cutting into a glacially striated seabed. These Arctic Ocean glaciogenic seafloor features show similarities to features mapped on the Antarctic continental margin, both regarding their morphology and dimensions. In this presentation, results from geophysical mapping in the Arctic Ocean with icebreaker Oden during the LOMROG 07 expedition and with USCGC Healy during the HOTRAX 05 and HLY0703 expeditions are presented and compared with published results from the Antarctic continental margin. On the Yermak Plateau, multibeam data from the LOMROG 07 expedition show subdued glacial striations, flutes, which are extending in a northwesterly direction towards the central Arctic Ocean. The mapped portion of the Yermak Plateau where the flutes exist is between 500-600 m deep. Chirp sonar profiles collected along with the multibeam bathymetry reveal that these flutes comprise the top of a glacially eroded surface which extends down to a water depth of approximately 830 m below present sea level, although the glacially eroded surface is draped by sediments from a depth of approximately 600 m. This suggests that the Yermak Plateau has been overridden by an ice sheet. Results from the nearby shallow continental margin suggest that the Svalbard ice sheet during the Last Glacial Maximum (LGM), however, never reached the deeper Yermak Plateau and, thus, the flutes must originate from older glaciations. On the Morris Jessup Rise deep iceberg scours are mapped down to a water depth of 1012 m. These iceberg scours cut across the Morris Jesup Rise and it is possible to see from the multibeam data that the deep drafting icebergs causing them came from a westerly direction. Studies of sediment cores acquired directly from the scours indicate that the scouring took place during Marine Isotope Stage (MIS) 6. On the Chukchi Cap the multibeam data from USCGC Healy show closely-spaced striations and bedform-like features at approximately 410 m depth at approximately 760 32\u27 N, 1630 49\u27 W. The striations are curvilinear and oriented roughly northwest-southeast. They are typically 1-3 m deep and spaced 100 � 200 m apart. The bedform-like features are about 10 m high with wavelengths of 1-2 km. These features, currently more than 660 km from the nearest coastline suggest the presence, at some time, of a grounded ice sheet on the Chukchi Cap. Conspicuous erosional channels found slightly deeper than the striations, possible suggest intense sub-glacial water flow. Taken together, the mapped glacial morphology combined with coring results providing chronostratigraphic information constrain the extents of former ice sheets and ice shelves on the continental margins respective deep Arctic Ocean during past glacial periods