Causes of the Abrupt and Sustained 2016–2023 Antarctic Sea-Ice Decline: A Sea Ice–Ocean Model Perspective

Antarctic sea ice, which undergoes large seasonal changes and plays a crucial role in the global climate system, showed a gradual increasing trend in its extent from the late 1970s to 2015 but experienced a sharp decline in 2016, followed by record lows in subsequent years. This study investigates the causes of the recent regime shift in Antarctic sea-ice extent (SIE) using a global sea ice–ocean model with 0.25° resolution forced by atmospheric reanalysis-based surface boundary conditions. Numerical experiments reveal that thermodynamic boundary conditions, particularly the increased subpolar sea surface temperatures (SSTs) north of the sea-ice edge, are the dominant drivers of Antarctic sea-ice decline. Additionally, wind stress partly contributes to the variability in summer SIE. These findings highlight that SST warming near the sea-ice edge, resulting from atmosphere–ocean interactions under ongoing atmospheric warming, plays a key role in the recent decline in Antarctic SIE.