Record low sea ice extent in the Weddell Sea, Antarctica in April/May 2019 driven by intense and explosive polar cyclones

Abstract

Abstract Sea ice extent (SIE) in the Weddell Sea attained exceptionally low levels in April (1.97 million km 2 ) and May (3.06 million km 2 ) 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 −1 s −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.