The Digester

A new analysis of 2005–2022 hydrographic and satellite data shows that multiyear thinning of Winter Water preconditioned the upper ocean, and a strong wind-driven mixing event in August 2015 pumped warm Circumpolar Deep Water into the surface layer, triggering an abrupt and sustained drop in Antarctic sea-ice area.

From 2005 to 2015 Antarctic Winter Water thinned at about 1.7 m per year as warm, salty Circumpolar Deep Water shoaled toward the surface.
Anomalous winter winds in August 2015 greatly increased mixing, entraining CDW heat and salt into the mixed layer and producing a peak wind-driven heat flux near 14 W m−2.
The injected subsurface heat and salt explain the abrupt sea-ice area decline that began in August 2015 and led to record low seasons from 2016 onward.
After 2015 upper-ocean salinity and temperature changes reduced stratification, weakening Winter Water's barrier effect and sustaining greater ocean-to-surface heat exchange.
Regions with prior shoaling of the WW–CDW interface switched from correlating with more sea ice to correlating with less sea ice, signaling a change in ocean-ice coupling.
Climate models struggle to reproduce the timing and size of these changes, so the authors call for sustained Southern Ocean observations and further study to determine if this is a long-term regime shift.

2015 wind burst unlocked warm water below and triggered Antarctic sea-ice collapse

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