Record Low Antarctic Sea Ice in Austral Winter 2023: Mechanisms and Predictability

• Main Authors: Espinosa, Zachary, Blanchard-Wrigglesworth, Edward, Bitz, Cecilia
• Format: Other/Unknown Material
• Language: unknown
• Published: Authorea, Inc. 2024
• Subjects: Antarctic; Austral; Southern Ocean; Weddell; Antarc*; Sea ice
• Online Access: http://dx.doi.org/10.22541/essoar.171466440.03718233/v1

Since 2016, Antarctic sea ice area (SIA) has set three record summertime minimums occurring in 2017, 2022, and 2023. These recent extremes culminated in a record low SIA anomaly in austral winter 2023, when SIA was over 2 million km^2 below climatology, resulting from negative sea ice concentration (SIC) anomalies centered in the Ross, eastern Weddell, and East Antarctic Seas. We show that a fully-coupled Earth System Model run with historic and anthropogenic forcing and nudged to observed winds over 1950-2023 reproduces the observed austral winter 2023 SIC anomalies. In a sensitivity test that had the impact of 2023 ENSO conditions removed via regression, we show that the 2023 transition from La Niña to El Niño had a negligible impact. Next, using an ensemble initialized on January 1st 2023 nudged to past years’ winds, we demonstrate that ~70% of the total Antarctic SIA anomaly was predictable six months in advance and driven by warm Southern Ocean sea surface temperatures that developed prior to 2023, with the remaining ~30% attributable to 2023 atmospheric circulation. Finally, an ensemble forecast suggests that Antarctic SIA is likely to remain significantly below climatology in austral winter 2024 due to continuing warm Southern Ocean conditions.