The impact of changes in sea ice advance on the large winter warming on the western Antarctic Peninsula

Over 1979–2007 near-surface air temperatures on the maritime western side of the Antarctic Peninsula have increased throughout the year, with the greatest monthly temperature rise of 1.7 °C dec−1 occurring in July as recorded at Faraday/Vernadsky (F/V) station (65.4°S, 64.4°W). The warming trend in this month has been the result of a loss of very cold days at the station with the average number of days with mean temperature below − 15 °C decreasing from 7 during 1979–1988 to 0.6 over 1998–2007. There is a high anti-correlation between temperatures at F/V and the extent of sea ice in July just to the west of the station. Passive microwave satellite imagery reveals that monthly ice concentrations here have decreased by up to 25% since the late 1970s creating a polynya-like feature along the west coast of the peninsula. Sea ice extent over the southern Bellingshausen Sea has decreased markedly during the late summer and early autumn so that there has been a lengthening of the ice-free season. Yet faster ice advance in June as a result of changes in the meridional component of the wind means that the overall ice extent in the Bellingshausen Sea in July (offshore of the F/V region) has not changed significantly. Years of extensive sea ice can occur as frequently now as in the earlier part of the record, but a combination of the changing nature of the ice advance and subtle shifts in the wind direction have led to the more frequent occurrence of the ice-free area to the west of F/V in recent years. There are also indications of pre-conditioning of the ice/ocean system to the west of F/V well before winter that is associated with the presence or absence of the ice anomaly that is observed in July.

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