Delayed responses of the oceanic Beaufort Gyre to winds and sea ice motions: influences on variations of sea ice cover in the Pacific sector of the Arctic Ocean

In the late 2000s, the dominant sea ice type in the Arctic Ocean changed from multi-year ice to first-year ice. In this condition, winter growth of first-year ice and resultant ice thickness at the melt onset are key preconditions on whether sea ice can survive or will disappear during the following summer. The growth rate strongly depends on upper ocean thermal conditions. In the Pacific sector of the Arctic Ocean, the warm Pacific Summer Water, which is a major heat source affecting the sea ice growth, is transported toward the basin by the oceanic Beaufort Gyre, driven by winds and sea ice motions, but the response time scale of the oceanic Beaufort Gyre to surface forcing has been unclear until now. In the present study, we examine the relationship between the ocean dynamic height near the Northwind Ridge as a proxy of the northward volume transport and curls of winds and sea ice velocities, using multiple regression models that evaluate relative contributions of past surface forcing to the current state of the oceanic Beaufort Gyre. As a result, the time scale of the delayed oceanic response in 2006-2012 was estimated to be about 3 years. Taking into account the response time scale, the multiple regression model using the satellite-derived sea ice motion data successfully reconstructed the observed variations of ocean dynamic heights within an accuracy of 0.2 dynamic cm, which corresponded to about 2 % of the amplitude of the observed variations.