Long-lasting impact of winter North Atlantic Oscillation on Barents-Kara sea ice anomaly in recent decades

In this paper, the long-lasting impact of the winter North Atlantic Oscillation (NAO) on Arctic sea ice is investigated using reanalysis data, with focus on the Barents-Kara (BK) sea where the air-sea-ice response is closely associated with the interdecadal shift in the northern action center of the NAO. A significant negative correlation between the winter NAO and the late autumn BK sea ice has been dominant since the early 2000s, which is in sharp contrast to the extremely weak correlation before the late 20th century. When the northern center of the NAO retreats westward, a prevailing low-level southerly wind anomaly creates significant positive air temperature anomalies over the BK sea, and the induced ocean current strengthens the northward transport of warm sea water, resulting in a positive BK upper-layer ocean temperature anomaly and a negative sea ice anomaly until early spring. Entering summer, the preexisting less-than-normal sea ice causes the amount of solar shortwave radiation absorbed by the upper-layer sea water to significantly increase and thereby continues to warm up the upper layer of sea water and reduce the sea ice. The warmed sea water enables the negative sea ice anomaly to last until late autumn owing to its relatively large specific heat capacity. Thus, the NAO in the previous winter exerts a long-lasting impact on the BK sea ice.