Climate and the Initiation of Maritime Ice Sheets

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Abstract
The lower latitude extension of polar water during Quaternary glaciations has two opposing effects on the mass balances of adjacent maritime ice sheets. Cooler air temperatures reduce ablation and increase the fraction of precipitation falling as snow, but also lead to reduced atmospheric moisture content and reduced precipitation. The effects of these contrasting processes on ice-sheet initiation are investigated using a coupled ice-sheet-atmospheric moisture model of the Loch Lomond ice sheet in Scotland (10 000 a B.P.). There is a delicate balance between the degree of cooling required to initiate ice accumulation and that which restricts the flow of moisture over the area. At the regional scale of Scotland, the combined effects of orographic enhancement and the inherent feedback between the rising ice-surface elevation and increasing mass balance are dominant, and ice-sheet growth accelerates. Comparison of the results from models using different wind directions suggests that south-westerly winds were prevalent during the Loch Lomond glaciation in contrast to the dominant westerly winds of the present day. The modelling experiments demonstrate the sensitivity and complexity of the links between ocean surface cooling and ice-sheet growth, particularly at the early stages of a glacial cycle.