Reflection seismic investigations of the Canadian Beaufort Sea margin, Arctic Ocean

The seismic stratigraphy and sedimentary architecture of the Canadian Beaufort Sea margin are investigated using a comprehensive grid of two-dimensional seismic reflection data. Three cross-shelf troughs, representing locations of former ice streams draining a 1000 km-long section of the Laurentide Ice Sheet (LIS), are examined: the Mackenzie, Amundsen Gulf and M'Clure Strait systems. These palaeo-ice streams operated during the last, Late Wisconsinan glacial maximum, as well as during a hitherto unknown number of earlier Quaternary glaciations. Their dynamics influenced past ice-sheet configuration and may have forced abrupt climate change through transport of ice and freshwater to the Arctic Ocean. The objectives of this work are to constrain the number of ice advances through each trough, to discuss the possible timing of these events, and to examine the impact of Quaternary glaciation on the continental shelf and slope. The implications of these data are discussed in relation to ice dynamics at the northwest LIS limit, the glacial history of the Canadian Beaufort Sea margin, and the geomorphological imprint of palaeo-ice streams. The number of Quaternary ice advances across the Canadian Beaufort Sea margin varies markedly between the Mackenzie Trough (two) and the Amundsen Gulf Trough (at least nine). The Mackenzie Trough was probably occupied by an ice stream during the Late Wisconsinan and either the Illinoian or Early Wisconsinan glaciation. The Amundsen Gulf ice stream was initiated earlier in the Quaternary. The architecture of the slope beyond the Mackenzie Trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacialsedimentary depocentre that is characteristic of slopes seaward of high-latitude cross-shelf troughs. In contrast, trough-mouth fans ( of volumes -10,000 km.3 and -60,000 km3) are present beyond Amundsen Gulf and M'Clure Strait, respectively. The location of 75 High Arctic cross-shelf troughs is presented together with a synthesis of their key physiographic characteristics and available glacial-geological evidence of past occupation by ice streams. The dimensions and architecture of the three troughs on the Canadian Beaufort Sea margin are compared to those of other High Arctic troughs. The Amundsen Gulf and M'Clure Strait troughs were probably two of the most significant cross shelf troughs in the High Arctic, in terms of their dimensions and palaeo-drainage basin areas. A number of buried glacigenic landforms, including grounding-zone wedges and lateral moraines, are identified from the Canadian Beaufort Sea shelf, recording the former positions of still-stands or re-advances in the ice margin. The youngest sequence of sediment in the Amundsen Gulf Trough is interpreted to have been deposited by a subsidiary ice stream, the Anderson ice stream, subsequent to Late Wisconsinan ice retreat through the Amundsen Gulf. This provides evidence of dynamic ice-stream behaviour and the reorganisation of the north west sector of the LIS during the last de glaciation.