No longer polar opposites: the Arctic and the Antarctic are converging towards a seasonally dominated sea-ice regime

Le résumé fourni par la source

Over the satellite period, Arctic and Antarctic sea ice extent seemed to follow opposite pathways. Arctic sea ice showed a strong and prolonged decrease until 2007 and then stalled in its rate of decline. Antarctic sea ice extent, on the other hand, displayed a small but significant increase until 2015. After 2015, Antarctic sea ice extent experienced a sharp decline, and has since been characterized by a lower mean state with enhanced variability, suggested as a new sea-ice regime. Arctic sea ice has continued transitioning towards a regime of substantially lower summertime coverage with reduced multiyear ice, increasingly resembling Antarctic sea ice in conditions and seasonality. We suggest that the parallel changes in Arctic and Antarctic sea-ice behavior share a common mechanism: the breakdown of ocean stratification sustaining sea-ice decline, whilst episodic atmospheric forcing increasingly influences high-frequency sea-ice variability. In both the Antarctic and the Eurasian Basin of the Arctic, positive sea surface salinity anomalies have caused a weakening of the ocean halocline. The associated erosion of stratification makes sea ice more vulnerable to subsurface heat, and appears to underpin recent sea-ice loss and elevated variability. The convergence of the two polar regions toward a seasonally dominated sea-ice regime leads us to call for enhanced knowledge transfer and coordination between polar communities to accelerate understanding of recent sea-ice changes. A better understanding of the mechanisms driving changes in the coupled atmosphere--ocean--sea-ice system is needed to improve projections of future sea-ice loss and assess the cascading risks it poses to global climate and regional ecosystems.

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