Summary
Net sea-ice extent (SIE; the area enclosed by greater than 15% sea-ice concentration) and sea-ice area (SIA; the product of sea-ice extent and concentration) were well below average or at record-low levels throughout 2023 (Fig. 6.11a). Monthly-mean low SIE and SIA records were significantly shattered for eight months in 2023 i.e., January, February, and May through October, and this is mirrored in the extreme curtailment of sea-ice growth around much of Antarctica during the autumn-winter advance season (Fig. 6.12a). The sea-ice deficit at a time of the year when the sea-ice zone should be growing is unprecedented in the satellite time series in both timing and magnitude. For example, net SIE was as much as ?2.9 × 106 km2 below the long-term (1991–2020; used throughout) mean on 6 July, ?1.8 × 106 km2 less than the previous record low for that date (in 2022; Reid et al. 2023). This situation is in contrast with the last seven years, starting with the first major downturn in Antarctic sea-ice coverage in 2016, when most record lows largely occurred during the late-spring through summer retreat/melt phase of the annual sea-ice cycle (Parkinson and DiGirolamo 2021). Regionally, SIE remained well below average almost everywhere apart from in the eastern Ross and Amundsen Seas for much of the year and in the Bellingshausen Sea for the second half of the year (Fig. 6.11b).
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