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A continuing trend for Arctic ice The annual freeze, thaw cycle for sea ice shows that the extent of the ice cover is following a roughly linear downward path ALAN BAILEY Petroleum News
Since satellite observations of the Arctic sea ice began in 1979, the message from the sea ice data has been clear: The area of the sea ice cover during the period of minimum ice extent in September has been declining quite consistently at an average rate of 13.4 percent per decade, according to data published by the National Snow and Ice Data Center. This year’s ice extent minimum of 1.7 million square miles was the fourth lowest on record. And the nine lowest September ice extents have all been observed in the last nine years, NSIDC has reported.
NSIDC says that the prelude to this year’s low September minimum was a record minimum winter sea ice extent, reached in February. And the summer melt season also began early, NSIDC says.
Multiyear ice But multiyear ice, relatively thick ice that has persisted for several years and that takes a significant time to melt, also played into this year’s ice extent situation. A relatively large amount of this multiyear ice moved into the Beaufort and Chukchi seas during the winter - the subsequent slow melt of this ice resulted in a somewhat larger September sea ice extent than would otherwise have been the case, NSIDC says. However, the onset of the summer ice melt began earlier than on average in the Beaufort Sea, especially along the Canadian coast, and in the Kara Sea, triggering an early ice retreat in these regions.
Strong winds during the spring in the eastern Beaufort Sea contributed to an early ice retreat in that region, NSIDC says.
Warm conditions The rate of ice loss accelerated in July because of overall warmer than average temperatures in the Arctic Ocean, although the ice was slow to melt in Baffin Bay and Hudson Bay. While temperatures were not particularly high in August, there were higher than average sea surface temperatures in September. On the other hand, sea surface temperatures were generally lower than average in the Nordic seas, NSIDC says.
However, the melting of the multiyear ice that had been transported into the Beaufort and Chukchi seas in the winter resulted in a 31 percent depletion in multiyear ice during the summer across the Arctic Ocean as a whole, compared with a 13 percent depletion in 2013 and a 38 percent depletion in 2012, NSIDC says. The presence of multiyear sea ice is important in terms of its impact on the annual ice melt and on the total volume of the sea ice, as distinct from just the areal extent of the ice.
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