Large-scale drivers of the exceptionally low winter Antarctic Sea Ice Extent in 2023

The year 2023 marked a turning point for the Antarctic region, as the Southern Hemisphere experienced a significant reduction in its sea ice cover, with a record-breaking sea ice minimum in July 2023 of ~2.4 million square kilometers below the long-term mean. This study investigates the drivers behind this exceptional event, by combining observational, satellite and reanalysis data. Throughout the year, the Antarctic Sea ice extent broke record after record, ranking as the lowest sea ice on record from January to September, with the exception of March and April. The exceptionally low sea ice extent from May to August was mainly driven by the prevalence of a zonal wave number 3 pattern, with alternating surface high- and low-pressure systems, which favored the advection of heat and moisture, especially over the Ross Sea (RS), Weddell Sea (WS), and Indian Ocean (IO). From May 2023 to August 2023, record-breaking low sea ice extent and high temperatures were recorded, and the most affected regions were RS, WS, and IO. Over the Weddell Sea, temperature anomalies of up to 10°C have been observed from May to July, whereas over the Ross Sea, temperature anomalies of up to 10°C have been observed, especially in July and August. A regime shift in the Antarctic Sea ice, as well as in the average mean air temperature and subsurface ocean temperature over the Weddell Sea, was detected around 2015. The analysis revealed complex interactions between atmospheric circulation patterns, oceanic processes, and their implications for variability and change in Antarctic Sea ice. Understanding the underlying mechanisms of these extreme events provides crucial insights into the changing dynamics of Antarctic Sea ice and its broader climatic significance.