Assessment of Heat Content and its Variability in the Arctic Halocline from the Regional Arctic System Model (RASM) and Observations

Abstract:

The decline of Arctic sea ice cover for the past decades has altered the surface energy budget due to decrease in the surface albedo and resulting increased absorption of short wave energy into the upper ocean. We hypothesize that heat content accumulating in the halocline layer (HL), defined as water below the surface mixed layer and above the Atlantic Layer, has been increasing in magnitude and area and it is a critical and ‘new’ source of energy, potentially further accelerating the ice cover decline. This heat content is due to convergence of Pacific summer water and local waters warmed via solar insolation. To address this hypothesis we analyze available observational data and output from two subsets of the fully coupled Regional Arctic System Model (RASM), where the atmospheric and land components are replaced with prescribed realistic reanalysis data. First, mixed layer and halocline depths are estimated from RASM and compared with available observational estimates. Next, monthly heat content is calculated in the HL for the period of 1948-2009. Model results indicate that heat content in the HL (i) is stored throughout the year, including winter and consistent with observations, (ii) is greatest in the western Arctic and (iii) experiences a positive trend in the Western Arctic with positive anomalies spreading northward out of the southern Beaufort Sea into the Canada Basin. We postulate that realistic representation of the HL heat content and its trends may help improve model simulation and prediction of the Arctic sea ice cover and climate change.