The deposition and disposition of solar heat in summer Arctic leads

Abstract:

Areas of open ocean within an Arctic sea ice cover absorb over 90% of the incident shortwave radiation. This absorbed solar radiation can contribute to warming in the upper ocean, lateral melting, bottom melting, or losses to the atmosphere. We examine the key drivers of these processes: the depth-dependent absorption of solar radiation and the horizontal and vertical mixing of this heat. We present observed profiles of temperature, salinity, density, and heat content of the top 5-20 m of summer leads. These profiles show occasional strong salinity-driven stratification, with freshening of the surface layer and temperatures a couple of degrees above freezing. Storms and the attendant ice motion erase the stratification, cooling water temperatures and enhancing ice melt. We use radiative transfer modeling to determine the depth-dependent deposition of solar radiation in the upper ocean and its relationship to cloud cover and water clarity. Sunny skies and turbid water enhance solar absorption in the top few meters of the lead. The impact of horizontal and vertical mixing on the disposition and fate of the absorbed solar heat is explored using a simple two-dimensional heat diffusion model.