Thinning of floating ice shelves with resulting unpinning and reduced buttressing of continental ice and grounding line retreat is potentially the largest contributor to sea-level change (Weertman, 1976; Thomas, 1979b; van der Veen, 1986). Ice-shelf thinning could occur from enhanced melting at the underside of ice shelves, which could result from changes in properties and circulation of the ocean caused by climate change (Jacobs et al., precede Heinrich events (Darby et al., 2002). Although very tentative, this suggests that the activity of the MCIS may have important implications for a lead-lag relationship whereby the northern margins of the LIS disintegrated prior to the eastern margins that produced the Heinrich events (Darby et al., 2002).
In addition to the IRD and meltwater input, the ice stream may also have influenced the formation of a large Antarctic-type ice shelf in the western Arctic Ocean, up to 1 km thick and covering hundreds of kilometres (Polyak et al., 2001). Evidence for such an ice shelf includes submarine bedforms indicative of glacial scouring and moulding of the sea floor around the Chukchi plateau in the western Arctic Ocean (Plate 26.2). The orientation of bed-forms points to a source emanating from the broad straits of the Canadian Arctic Archipelago, suggesting possible interactions with the ice stream (cf. Polyak et al., 2001). However, the evolution and size of this Arctic ice shelf are yet to be constrained. Given the strong evidence for several phases of iceberg delivery from the ice stream, it is likely that icebergs were able to bypass this ice shelf en route to the Fram Strait. Further work to determine the age and extent of an Arctic Ice Shelf will help to elucidate the pos-sible interactions between the MCIS, iceberg delivery and Arctic Ocean IRD events. These developments may feed into our knowledge of the interactions between West Antarctic Ice Streams and the ice shelves they currently nourish.
1992). Melt rates near the grounding lines of deep-draft outlet glaciers are particularly relevant to ice sheet mass balance because continental ice discharge is controlled by the channelized flow of these ice streams into the ocean. If these regions are the locus of high basal melting, the potential exists for substantial ocean control over ice shelf, if not ice sheet, mass balance. Model simulations indicate that for moderate global warming, resulting in
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