In Austral summer 2016/2017, the sea ice extent (SIE) in the Weddell Sea dropped to a near‐record value in the satellite era (1.88 × 106 km2), a large negative seasonal anomaly that persisted in an unprecedented fashion for the following three summers. Various atmospheric and oceanic factors played a part in the change. Ice loss started in September 2016 when the northern Weddell Sea experienced westerly winds of record strength, advecting multiyear sea ice from the region. In late 2016, a polynya over Maud Rise contributed to low SIE over the eastern Weddell Sea. With extensive areas of open water early in the summer, upper ocean temperatures increased by ~0.5°C, with the anomalies persisting in subsequent years. The reappearance of the Maud Rise polynya in 2017, high ocean temperatures, and storms of record depth kept the summer SIE low.

Antarctic sea ice extent (SIE) has displayed a complex pattern of change over the period for which we have reliable data from passive microwave satellite instruments starting in the late 1970s. Until the mid-1990s there was no significant trend in the annual mean total Antarctic SIE or the extent at the annual minimum (Figure 1a). However, this was followed by an upward trend in both measures, which was accompanied by an increase in the inter-annual variability (Fogt et al., 2022, Figure 1). The overall increase in SIE between the mid-1990s and 2014 masked large regional variations, such as the increase in the Ross Sea and decrease in the Amundsen-Bellingshausen Seas (ABS) (Turner et al., 2015), which was consistent with a deepening of the Amundsen Sea Low (ASL) (Raphael et al., 2015). A number of studies have examined the sea ice increase and suggested it was linked to a range of high latitude and tropical forcing factors (

Long-term water mass changes during 1994-2012 are examined from nine repeat hydrographic sections in the Seasonal Ice Zone along 140 degrees E, off Antarctica. Significant freshening trends are detected within most of the water masses from the bottom to surface. Bottom Water freshened by 0.008-0.009 decade(-1) below isopycnal surfaces and its layer thickness decreased by 120-160 dbar decade(-1) throughout the study period. In addition to general thinning, the layer thickness was anomalously thin in 2012, suggesting a possible link with the sudden calving of the Mertz Glacier Tongue and subsequent reduction in sea-ice production. Winter Water freshened by 0.03 decade(-1) throughout the study period, with significant interannual variability. In the offshore region, a long-term increase in precipitation can explain a substantial portion of the freshening trend. The Lower Circumpolar Deep Water on the continental slope underwent freshening at the same rate as the Bottom Water during the last two decades. Modified Shelf Water also shows robust freshening at a rate of 0.03 decade(-1). Combined with the freshening of near-surface and Bottom Water masses in this region, these data indicate freshening of the entire water column over the continental slope. This widespread freshening is broadly consistent with the enhancement of the global hydrological cycle, together with a possible acceleration of land ice melting

Sea ice extent (SIE) in the Weddell Sea attained exceptionally low levels in April (1.97 million km2) and May (3.06 million km2) 2019, with the values being ~22% below the long-term mean. Using in-situ, satellite and atmospheric reanalysis data, we show the large negative SIE anomalies were driven by the passage of a series of intense and explosive polar cyclones (with record low pressure), also known as atmospheric ‘bombs’, which had atmospheric rivers on their eastern flanks. These storms led to the poleward propagation of record-high swell and wind waves (~9.6 m), resulting in southward ice advection (~50 km). Thermodynamic processes also played a part, including record anomalous atmospheric heat (>138 W m−2) and moisture (>300 kg m−1s−1) fluxes from midlatitudes, along with ocean mixed-layer warming (>2 °C). The atmospheric circulation anomalies were associated with an amplified wave number three pattern leading to enhanced meridional flow between midlatitudes and the Antarctic.