How Atlantic heat makes Arctic sea ice retreat

How change comes to Arctic sea ice still remains mechanistically and prognostically unresolved. Here we provide observational and physically consistent evidence that sea ice variability and retreat north of Svalbard result from Atlantic water impinging directly on the oncoming transpolar sea-ice drift. We particularly show that the local halocline is largely maintained by local sea ice melt and that the winter sea-ice extent can be predicted from the upstream temperature of the Norwegian Atlantic Current one year in advance. The latter scaling also relates to trends; the long-term 1 ºC warming of Atlantic water over the last 40 years is reflected in 50.000 km² sea-ice retreat north of Svalbard and into the Nansen Basin. Zooming out to the Arctic Ocean in general, and considering the projected future in a large-ensemble climate model simulation, we find that this “Atlantification” of the Arctic will progress throughout the 21^st century but apparently restricted to the Eurasian Basin by the natural barrier of the Lomonosov Ridge.