Effects of wind and sea ice on the seasonal variation of warm circumpolar deep water in the Amundsen Sea

Abstract

Spatial and temporal variation of the layer of warm and salty circumpolar deep water (CDW) in the center of the Amundsen Shelf was measured during two oceanographic surveys and a two-year mooring array. A hydrographic transect from the deep ocean, across the shelf break, and into the Dotson Trough shows a local elevation of the warm deep water layer at the shelf break. In the deep channel, the thickness of the CDW's warm layer varies strongly with season, attaining maximum thickness in austral summer and waning to a minimum in austral winter. The amplitude of this seasonal variation of the interface is up to 60 m. The seasonal variation in thickness of this warm layer gives rise to a seasonal variation of the CDW's heat content. To investigate the effects of wind and sea ice on the seasonal variation of the heat content, a simplified ocean surface stress model was used. Fields of Ekman pumping velocity were obtained from the ocean surface stress. The Ekman pumping at the shelf break, where the warm layer is elevated, shows a strong seasonal variation coinciding with the mooring data. From February to April, the marginal ice zone is close to the shelf break, and the wind field is eastward, giving rise to a strong positive Ekman pumping that may explain the seasonal signal seen in the mooring data. During austral winter, the marginal ice zone is further north, so the Ekman pumping does not cause any flow of warm water onto the shelf.