Role of Intense Arctic Storm in Accelerating Summer Sea Ice Melt: An In Situ Observational Study

Abstract

Intense storms have been more frequently observed in the Arctic during recent years, in coincidence with extreme sea ice loss events. However, it is still not fully understood how storms drive such events due to deficient observations and modeling discrepancies. Here we address this problem by analyzing in situ observations acquired during an Arctic expedition, which uniquely captured an intense storm in summer 2016. The result shows a pronounced acceleration of sea ice loss during the storm process. Diagnostic analysis indicates a net energy loss at the ice surface, not supporting the accelerated melting. Although the open water surface gained net heat energy, it was insufficient to increase the mixed-layer temperature to the observed values. Dynamic analysis suggests that storm-driven increase in ocean mixing and upward Ekman pumping of the Pacific-origin warm water tremendously increased oceanic heat flux. The thermal advection by the Ekman pumping led to a warmed mixed layer by 0.05 degrees C-0.12 degrees C and, in consequence, an increased basal sea ice melt rate by 0.1-1.7 cm day(-1).

Plain Language Summary More numerous storms have occurred over the Arctic during recent years, potentially impacting sea ice. Few studies have investigated the role of storms in sea ice change based on field observations. Our study aims to address the problem through analyzing changes in sea ice energy budgets during a strong storm event in summer 2016 that was associated with a rapid sea ice loss. Both atmosphere and ocean observational data were collected during a research vessel expedition in the Arctic Ocean. We found that the storm resulted in an overall heat loss from the sea ice surface to the atmosphere but a strong heat gain at the sea ice bottom from the upper ocean. Storm-induced strong anticlockwise winds drove a divergence in the upper ocean, which led to a shallowed mixed layer and enhanced mixing with the sub-surface warm water, and, in turn, an acceleration of sea ice bottom melt.