Trapped Heat and Cooling Processes in the Arctic Ocean Surface Mixed Layer

Abstract:

With the changing Arctic climate, sea ice is disintegrating earlier and there is an increasing length of time during which the ocean is exposed to solar radiation. The surface mixed layer of the Arctic Ocean is reaching unprecedentedly warm temperatures. This study examines the cooling processes in the summer mixed layer of the upper ocean between the warm late-summer and the onset of ice growth. In situ measurements of upper ocean temperatures from UpTempO buoys and a number of CTD profiles in the Beaufort and Chukchi regions indicate that as expected, most of the heat in the upper ocean is lost to the atmosphere at the surface. Cooling to the atmosphere occurs predominantly through sudden cooling events associated with passing weather systems, with cooling rates greater than 0.2 °C/hour. However, a not-insubstantial amount of heat gets trapped in the summer halocline forming temperature features like the Near Surface Temperature Maximum isolated from the cooling associated with passing storms. These are clearly visible in the included figure. They come and go over the course of the cooling season, but typically persist through freeze-up. Heat stored in this layer will, on erosion of the summer halocline with wintertime ice growth, be mixed into the surface mixed layer and slow the growth of sea ice. This presentation quantifies the relative balance between heat loss to the atmosphere, temporary and seasonal heat storage in the summer halocline, and the relationship to fall season storminess in the region.