Sea-ice extent in the Arctic and Antarctic at an average level
14 Feburary 2020
Though the sea ice was at a record minimum in terms of its mean monthly extent in October, ice growth increased substantially in November and December, reaching a size that is roughly average for the month of December. In January 2020 the mean sea-ice extent was 13.42 million km², i.e., ca. 0.97 million km² below the long-term average for the month (see Figures 1 and 2). In January the ice cover in the Arctic showed a comparable development to that seen in the past several years; at 14.40 million km² on 12 February, it was at the lower edge of two standard deviations from the long-term average for 1981 – 2010 (see Figure 3). Since the sea-ice extent in the Arctic is naturally limited by the coastlines of adjacent landmasses, the ice can only expand in the Atlantic sector, in the Barents, Bering and Greenland Seas, in the Sea of Okhotsk, and in the Davis Strait to the west of Greenland. Compared to 2018, this year the sea-ice extent was higher in the Barents, Bering and Greenland Seas, but lower in the Davis Strait and the Sea of Okhotsk (see Figure 4).
The air temperature over the Arctic Ocean at 925 hPa (ca. 762 m) was 1 to 3 °C higher than the long-term average. Further, major expanses of Siberia were much warmer than usual for this time of year. Conversely, the air temperature was 5 to 6 °C below average in the northern Barents Sea and southern Alaska. Further, temperatures were below the long-term average in Greenland and most of the eastern Canadian Arctic Archipelago (see Figure 5). Pressure at sea level was unusual: a low-pressure cell covered the North Atlantic, reaching to the Kara Sea. At the same time, a high-pressure cell extended from Eurasia to Alaska and northern Canada. The atmospheric pressure over the Kara Sea at 9 hPa was below the long-term average for the period 1981 to 2010. This was most likely the result of an intensely positive Arctic Oscillation, which continued for most of the month. By late January the Arctic Oscillation index was once again nearly neutral.
Sea-ice extent in the Antarctic nearing its minimum
In the Antarctic, too, the sea-ice extent seems to be developing in keeping with the long-term average. The current sea-ice extent is ca. 2.91 million km² (Figure 6). The mean value for January was 4.27 million km², i.e., roughly 688,850 km² below the long-term average for 1981-2010 (Figures 7 and 8). Although December 2019 was characterised by the third-lowest sea-ice extent since the beginning of continuous satellite observation in 1979, the trend did not continue in January (Figure 8); especially in the central and eastern Ross Sea, the areas covered by sea ice were larger than in the past several years. Moreover, the entire pack-ice belt surrounding the Antarctic is somewhat more pronounced this year. In the course of January, the sea-ice retreat increasingly slowed, most likely due to relatively cool atmospheric temperatures in the circum-Antarctic coastal sector. If this trend continues, we can expect to see a summer minimum sea-ice extent in the Antarctic that is within the range of the long-term trend, which would break up the pattern observed in the last three to four years, namely, a string of historically low mean monthly sea-ice extents scattered throughout the year. However, it won’t be possible to analyse this aspect in detail until the end of February, by which time the summer minimum will have come and gone.
Experts returning from the first leg of MOSAiC report on the progress made
When the Kapityn Dranitsyn arrived at the MOSAiC camp on 13 December 2019, she brought with her the first replacement team for the expedition, and on 18 December the new team of researchers commenced work on and near the MOSAiC floe. Dr Marcel Nicolaus, co-expedition leader for the first leg of the journey, recaps this exciting first chapter in the MOSAiC story as follows: “Finding ‘the’ MOSAiC floe was surely a major milestone for everyone involved in the project, and for all of the readings and samples we’ll be collecting in the course of the year. We’re happy to have found a highly suitable candidate, one that not only represents the typical ice conditions in the Arctic in recent years, but also meets our complex logistical requirements. We’re confident that we’ll be able to drift the entire year with this floe, and to gather a wealth of unique and exciting datasets in the process. It was fascinating to experience the Arctic in the heart of winter, and especially to see just how dynamic the entire system is. It took a great deal of hard work and improvisation from everyone involved to set up the camp in such a way that we can now conduct research with it, and in it, a whole year long. And we’re even happier to see that the plans we spent five years preparing have been implemented so well. The end of our part of the expedition marks the true beginning of this exciting and unprecedented year for sea-ice and climate research.”