Reversing Antarctic sea ice loss depends on ocean layering, study finds

Satellite observations have documented a pronounced decline in Antarctic sea ice extent since 2014, with especially sharp losses in recent years. Whether Antarctica's declining sea ice can recover hinges not only on how much carbon dioxide we emit, but also on how stratified the Southern Ocean is, according to new research published in Geophysical Research Letters.

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The scientists ran climate model experiments using the Coupled Model Intercomparison Project Phase 6, approximating future carbon dioxide stabilization and reduction pathways, starting from different initial states of ocean stratification around Antarctica. That is, they compared what happens if the Southern Ocean is already strongly stratified versus less so if carbon dioxide emissions begin to plateau or decline in the future. The goal was to test under what conditions Antarctic sea ice decline is reversible—or whether the system may cross thresholds beyond which recovery becomes difficult or very slow.

They found that the stronger the initial stratification during elevated atmospheric carbon dioxide levels, the more heat was stored in the surface open ocean layer, rather than being mixed downward, leading to accelerated sea ice melting. This melting enhanced ocean stratification further, leading to additional sea ice loss and creating a positive feedback loop, even when carbon dioxide emissions are reduced.

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The fate of Antarctic sea ice is not just about ice: it influences global climate, ocean circulation, ecosystems, and sea level. For example, less ice means more open water in summer, which absorbs more solar energy and further warms the ocean (ice‐albedo feedback). Warmer surface waters can accelerate the melting of ice shelves from below, increasing the discharge of land ice and promoting sea level rise. Sea ice also supports specialized ecosystems that depend on its presence, thus posing risks to the organisms that call it home.