Multibearn bathymetry and 3.5-kHz sub-bottoin profiler data collected from the US icebreaker Healy in 2003 provide convincing evidence for grounded ice on the Chukchi Borderland off the northern Alaskan margin, Arctic Ocean. The data show parallel, glacially induced seafloor scours, or grooves, and intervening ridges that reach widths of 1000 in (rim to rim) and as much as 40 m relief. Following previous authors, we refer to these features as “megascale glacial lineations (MSGLs).” Additional support for ice garounding is apparent from stratigraphic unconformities, interpreted to have been caused by ice-induced erosion. Most likely, the observed sea-floor features represent evidence for massive ice-shelf grounding. The general ESE/WNW direction of the MSGLs, together with sediment, evidently bulldozed off the Chukchi Plateau, that is mapped on the western (Siberian) side of the plateau, suggests ice flow from the Canada Basin side of Chukchi Borderland. Two separate generations of glacially derived MSGLs are identified oil the Chukchi Borderland from the Healy; geophysical data. The deepest and oldest extensive MSGLs appear to be draped by sediments less than 5 in thick, 1,whereas no sediment drape call be distinguished within the resolution of the sub-bottom profiles oil the younger generation. (c) 2005 University of Washington. All rights reserved.

At least two episodes of glacial erosion of the Chukchi margin at water depths to ∼450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide

Deep-sea sediments recovered from six sites visited during the International Arctic Ocean Expedition of 1991 were examined to determine sedimentation rates in the eastern Arctic Ocean basin. The dearth of age-diagnostic biogenic material in these sediments precludes the application of biostratigraphic methods, but ages can be deduced using paleomagnetism, in conjunction with measurements of radiocarbon and carbonate concentration. Although no one of these techniques gives an unambiguous determination of age, the interpretation most consistent with these diverse data implies that sedimentation rates in the eastern Arctic are, in general, a few centimeters per thousand years. Such estimates of sedimentation rate are an order of magnitude greater than those previously determined from many sediment cores taken from the Canada Basin. However, one site examined on the Morris Jesup Rise shows a relatively low rate of sediment accumulation (less than 0.6 cm/103 yr) suggesting that, although higher than in the Canada Basin, sedimentation rates in the eastern Arctic can be highly variable. (C) 1996 University of Washington.