Summary
During 2021, and following on from 2020, net Antarctic sea ice coverage continued to exhibit strong variability (Fig. 6.11a), with distinct regional and seasonal contributions (Fig. 6.11b). The year began with below-average overall sea ice extent (SIE) in January through February (Fig. 6.11a), compared to the 1991–2020 average, but abruptly switched to above average in late February where it remained almost continuously until early September. Sea ice then retreated at rates faster than average, with net SIE at ~1.5 × 10 6 km 2 below average in late December. Annual daily minimum SIE occurred on 22 February (2.68 × 10 6 km 2 ), which was slightly below average, while the annual daily maximum (18.79 × 10 6 km 2 ) was slightly above average but very early (30 August)—the second earliest daily maximum on record. Sea ice area (SIA), which is the product of SIE and concentration, followed a similar overall pattern to SIE but attained near record-high levels in late August (second highest on record), before plummeting to record-low daily values during parts of October and December. A new monthly-mean low SIA (5.45 × 106 km 2 ) was recorded for December. In terms of regional contributions, the western Weddell, Bellingshausen, and Ross Seas sectors generally experienced smaller-than-average SIE through much of 2021, whereas the Amundsen Sea sector recorded larger-than-average SIE through the year.
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