Researchers analyzing an observationally constrained sea ice–ocean model have identified a three-phase collapse in Antarctic sea ice. After decades of relative stability, the ice extent began a sharp decline in 2015, eventually hitting a post-1970s minimum in 2023. This shift represents one of the largest climatic transitions currently occurring within the Earth system.

Intensifying westerlies triggered the process by driving the upwelling of warm, saline circumpolar deep water (CDW). This subsurface heat mixed into the upper ocean, particularly affecting East Antarctica. While West Antarctic ice loss also faced pressure from longwave radiative flux anomalies, the primary driver involved a breakdown in ocean stratification that allowed deep heat to reach the surface.

Reduced freshwater export from melting ice has failed to stabilize the region. Instead, increasing salinity in the upper 100 meters of the water column actively weakens the stratification that once protected the ice. These persistent upwelling conditions, fueled by anthropogenic forcing, appear to be locking the Southern Ocean into a prolonged state of low sea ice cover.