Contribution of the deepened Amundsen sea low to the record low Antarctic sea ice extent in February 2022

The annual minimum Antarctic sea ice extent (SIE) in February 2022 hits a record low in the satellite era, with less than 2 million square kilometres observed on 25 February 2022, contrasting with the slightly positive trend in the Antarctic SIE prior to 2014. However, the preceding Amundsen Sea Low (ASL) in austral spring 2021 was the deepest since 1950. According to a linear regression model, the very low ASL contributed about 60% to the record low SIE in 2022. This study further investigates the underlying mechanism. The investigation of the lagged impact of the ASL on Antarctic SIE is based on observational data and state-of-the-art simulations. We found that (a) the deepened ASL associated with strengthened southerly winds accelerates the sea ice export away from the western Antarctic continent in spring, leading to the expansion of coastal polynyas (open water areas); (b) through the positive ice-ocean albedo feedback, the lack of the sea ice off the coastline enhances solar heating in the upper ocean and further sea ice melting in summer can occur. Specifically, in spring 2021, the deepest ASL is accompanied by a large sea-ice area flux of about 17.6 x 10(3) km(2) across 70 degrees S over the Ross Sea in October and November, contributing to a significant increase in net surface radiation of 20-30 W m(-2) and upper ocean warming of about 0.5 K in summer. Therefore, the deepened ASL in spring 2021 plays a crucial role for the record low Antarctic SIE in February 2022. In addition, it is found that both the La Nina conditions and the strong stratospheric polar vortex contributed significantly to the very strong ASL in 2021. Currently, nearly 2/3 of Earth system models in the Coupled Model Intercomparison Project Phase 6 have difficulties capturing the relationship between the ASL and the Antarctic SIE.