In general, the Arctic Ocean climate during the LGM featured cold winters, while summers were mostly dry and cooler than present. Mean annual SATs over the Arctic Ocean ranged between -19 °C and -26 °C as implied from amino acid analysis of molluscs (Barry, 1989). Ice conditions in the Arctic Ocean during the LGM are still poorly known and controversial. One hypothesis is that there were large floating ice shelves, up to 2-3 km thick, over the trans-oceanic ridges. This is evidenced by deep ice scouring on the ridge crests, as discussed below. A contrary hypothesis is that there was thick perennial sea ice, such as occurs off northern Canada at present (Clark, 1982). That sea ice was at least more extensive than at present is well documented. For example, de Vernal and Hillaire-Marcel (2000) provide evidence of extensive perennial sea ice along the continental margins of eastern Canada.
The idea of an Arctic Ocean ice sheet and large floating ice shelves was first advanced by Mercer (1970) and has been restated by Grosswald and Hughes (1999). One piece of supporting evidence is the widespread occurrence of abiotic conditions in the ocean sediments associated with the LGM. Glacial moulding and scouring of landforms and the fluting or erosion of ridge crests has been identified at 1 km depth on the Yermask Plateau, Chukchi Borderland and the Lomonosov Ridge by seabed mapping using side-scan sonar (e.g., Polyak et al., 2001). Grosswald and Hughes (1999) propose that the collapse of this ice shelf would have eliminated back pressure on ice streams in the Barents-Kara Sea Ice Sheet allowing fast flow and iceberg calving. They also suggest that in the central Siberian Arctic, where the ice shelf was grounded against the continental shelf, it dammed the Eurasian rivers flowing to the Arctic creating proglacial lakes and periodic flood events to the south (Grosswald, 1999). Kriner et al. (2004) show that large ice-dammed lakes in northwest Eurasia around 90 ka could have lessened summer melt on the southern margins of the Barents Sea Ice Sheet, by inducing cooling. In the mid 1960s, there was discussion in the Soviet Union and Canada about the local climatic role of the proglacial lakes in North America in the final phase of the last glaciation (Barry and Andrews, 1967). However, this conceptual model is at variance with the synthesis put forward by Siegert (2001).
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