The edge of the compact pack ice in the Arctic retreated to behind the 88th parallel, bringing it to just over 200 kilometres away from the North Pole. While this year’s sea ice cover is larger than that recorded in 2012, it does not signal a reversal in the trend. Elke Bunge in Berlin explains why.
The moment of truth has arrived. This is when the arctic summer will have melted the largest amount of winter ice in the Arctic Ocean and when the Arctic sea ice is reduced to its smallest extent, leaving only multi-year ice. Over the last few years there has been a growing number of negative records.
Another negative record
Sea ice physicists Marcel Nicolaus from the Alfred Wegener Institute, Helmholz Centre for Polar and Marine Research (AWI) and Lars Kaleschke from the University of Hamburg, KlimaCampus (Climate Campus) have recorded an unusual situation this year. The edge of the compact pack ice – which is the term used to describe areas with more than 90 per cent ice coverage – retreated north of the Russian group of islands Franz Josef Land and Severnaya Zemlya to behind the 88th parallel. This is the first time this has been recorded since the start of satellite measurements, explain the two physicists. Moreover it is possible to see increasing numbers of large areas of open water between 87 and 88 degrees north, i.e. still some 220 kilometres away from the North Pole. In the 1990s the edge of the summer pack ice was still at around 80 to 80 degrees north.
“These phenomena demonstrate a fundamental change in the Arctic ice cover. Seasonal ice can now predominantly be found where thick multiyear pack ice once prevailed,” explains Kaleschke.
More ice this year
The annual minimum sea ice cover in the Arctic Ocean this year is on average around 5.1 million square kilometres, some 50 per cent above the previous negative record of 3.4 million square kilometres recorded in 2012. But the physicists caution that this “figure does not signal a reversal in the trend. In fact, they believe that the ice extent observed is in line with the low readings in recent years and confirms the long-term reduction in Arctic sea ice.
“We did not expect a new negative record for the sea ice extent this year because statistics show that a short-term recovery always follows a record year,” says Kaleschke. “For this reason it is only possible to correctly record trends over longer periods of time.”
Significant fluctuations expected
Changes to the summer ice extent from year to year are the result of a complicated interaction: “The ice conditions in the spring, the course of the melting season and the atmospheric conditions in the summer are key factors here,” explains Nicolaus. Bearing this in mind, scientists also anticipate great fluctuations in summer ice cover in the Arctic in coming years.
Of particular concern to the physicists are the melt ponds on the sea ice, which have been appearing in greater number again as in previous years. Melt ponds are formed when the snow on the sea ice and then the sea ice itself melt from above. If this melt water cannot run off, it collects in pools on the sea ice.
“This has a substantial impact on the sea ice. White ice is transformed to darker ponds which absorb more sunlight and thus reinforce melting,” says Nicolaus.
Melt ponds are a normal phenomenon on the Arctic sea ice, but they are now occurring earlier in the year and for a longer period. Together with a sea ice extent that continues to retreat towards the North Pole, they are an ominous sign for the future of the Arctic Ocean.
Picture: Stefan Hendricks / Alfred Wegener Institute