Sea-ice extent in the Arctic at a historical low
27. July 2020
This May and June, the Arctic was dominated by a cell of warm air over the Siberian coast, which produced temperatures far above the long-term average (see Fig. 1). Consequently, temperatures up to 6 degrees Celsius or more above the long-term average were prevalent on the East Siberian coast, which led to early snow melting and thawing soils (you can find more information here). In June, these warmer temperatures also intensified sea-ice retreat in the Laptev Sea, a phenomenon that spread to the East Siberian Sea in early July. By mid-July the ice cover had retreated to such an extent that, for the first time this year, the Northeast Passage was completely open (Fig. 2). If we take a closer look at the sea-ice extent in the sector from 30° to 180° East, i.e., the Russian Arctic, we can see a historically low level for this region and time of year (Fig. 3). “In this sector of the Arctic we’re currently seeing 1 million km² less ice than the average for the past seven years. If you bear in mind that the summertime minimum sea-ice extent can drop below 4 million km², then a quarter of that area is already gone. But of course this alone isn’t enough to make a prediction for the September minimum,” explains Dr Gunnar Spreen from the Institute of Environmental Physics at the University of Bremen. The stable atmospheric pressure system over the Arctic helped to strengthen the warm-air cell, which led to intensified melting of the snow cover on the ice, and with it, to an earlier breakup and melting of seasonal ice (Fig. 4). Since the beginning of July, conditions have changed: there is a high-pressure cell over the East Siberian and Chukchi Seas, accompanied by unusually warm temperatures (up to 6 degrees Celsius) over the Central Arctic (Fig. 5).
In terms of how this development could affect the MOSAiC expedition, according to sea-ice physicist Dr Marcel Nicolaus: “Introducing so much warmth into the system so early in the year has accelerated the melting of the ice, which has also been worsened by the low albedo at this time of year, which produces an especially pronounced feedback. Accordingly, it should be very interesting when we start analysing our extensive field data. At the moment, we’re closely monitoring how our MOSAiC floe is melting in the marginal ice zone. To the best of my knowledge, this is the first time that the melting has been consistently monitored up to the point at which the ice completely disappears.” Both Marcel Nicolaus and Gunnar Spreen are currently in quarantine at a hotel in Bremerhaven in preparation for the last leg of the MOSAiC expedition. Both participated in the first leg, which began in September 2019 and focused on selecting the ideal floe for the drift experiment. “By now, the floe is nearing the end of its life, and we’ve succeeded in monitoring it throughout its entire lifecycle. Soon we’ll depart to observe the last quarter of the year in the Arctic – the early freezing and formation of new ice after the summer – just as intensively,” Nicolaus explains.
On 19 July 2020 the sea-ice extent amounted to 6.25 million km² in the Arctic, putting it ca. 570,000 km² below the previous minimum in 2019 (Fig. 4). This equates to an area the size of France and demonstrates the unusually low seasonal ice cover. This difference reached on 22 July even a value of ca. 614.000 km². As a result, the ocean in the ice-free areas will grow increasingly warm, promoting ice melting in adjacent areas. The prolonged stable weather conditions, together with a cell of warm air that has now spread to the Central Arctic, can be clearly seen in the sea-ice concentration map (Fig. 2). In large areas of the Arctic’s Russian sector, ice concentrations below 80 – 90 % can be seen, which represent a partial fragmentation of the ice cover. Melting snow cover, combined with the formation of numerous meltwater pools, changes the albedo of the ice’s surface, accelerating the melting process.
Dr Marcel Nicolaus (AWI)
Dr Gunnar Spreen (IUP)
Dr Christian Melsheimer (IUP)
Dr Renate Treffeisen (AWI)
Dr Klaus Grosfeld (AWI)