Arctic spring begins with moderate ice conditions
21 April 2020
On 4 March 2020, the Arctic sea-ice extent reached its winter maximum at 14.98 million km² and has been steadily declining ever since. The value is now hovering near the bot-tom limit of two standard deviations and is slightly above the values from 2019 (see Figure 1). The mean value for March was 14.51 million km² (see Figure 2), which is only ca. 200,000 km² above the value for last year (see Figure 3). The average daily sea-ice loss in March was roughly 23,000 km², or approximately the area of Mecklenburg-Vorpommern. In the last 42 years, since data has been collected from satellite observations, the Arctic has lost 1.64 million km² of sea-ice extent in the combined months of March (Figure 3), roughly equivalent to the area of Alaska. This equates to a loss of ca. 385.000 km2 per decade and 2.5 percent of the long-term average. Lower-than-average sea-ice concentrations were observed in the Bering, Greenland and Barents Seas (Figure 4).
In March 2020, the air temperature over many regions of the Arctic Ocean at 925 hPa pressure altitude (see Figure 5), at 2 to 3 C°, was below the long-term average, and up to 5.4 C° below the mean values in the Spitsbergen region (see Figure 6). Only in the Sea of Okhotsk and in the Bering Sea were temperatures up to 6 °C above the long-term aver-age. The atmospheric pressure at sea level was very low, due to a strongly positive Arctic Oscillation (AO), which prevailed through most of last winter (see Figure 7).
That being said, these trends are largely irrelevant for the ice conditions in the MOSAiC Ice Camp. Though the month of March was colder than the long-term average in the Central Arctic and the ice concentration chart for the region shows nearly 100 % ice cover, the small-scale ice conditions are highly dynamic. The ice has been in constant motion since mid-March, and extensive systems of cracks and leads have formed in the Camp area. Not only can broad leads and lakes be seen, but also pack-ice hummocks produced by colliding ice sheets; the latter have made on-site fieldwork much more difficult, in some cases cutting off monitoring stations’ power supplies, or even making them inaccessible. As a result, new solutions have to be found on a daily basis, in order to continue the work at the observatories: a challenge for research, logistics and equipment.
Sea-ice development since the summer minimum in the Antarctic
Since reaching this year’s minimum (2.68 million km² on 19 February 2020), the Antarctic sea-ice extent has recovered rapidly, and is now showing a very similar development curve to the long-term average. This marks the end of a phase characterised by below-average sea-ice extent (see Figure 9). At 4.0 million km², the mean value for this March was ca. 267,000 km² below the long-term trend, but continued the trend of minor growth since the record minimum in 2017 (Figure 10). Sea-ice growth was observed along the entire Antarctic coastline, particularly in the regions of the Ross Sea and eastern Weddell Sea. However, the sea-ice extent in both regions is below the long-term average (see Figure 11). Air temperatures over most coastal areas in the Antarctic were within roughly 1°C of the long-term average for the years 1981 to 2010, and near the southern Antarctic Peninsula they were (at 1°C to 3°C) slightly above the average. Significantly, colder-than-average temperatures were observed in the Wilkes Land region: 4°C to 6°C below the long-term average (see Figure 12). The atmospheric circulation pattern was somewhat unusual, and was dominated by a major low-pressure cell over the Amundsen and Ross Seas, and by a further low-pressure cell to the north of Queen Maud Land . In both areas, offshore winds produced by these cells correlated with more rapid ice growth. In keeping with the pronounced cell over the Amundsen and Ross Seas, the Southern Annular Mode index was positive.