A model for the Artic mixed layer circulation under a melted lead: Implications on the near-surface temperature maximum formation

Abstract. Leads in the sea ice pack have been extensively studied due to their climate relevance. An intense heat exchange between the ocean and the atmosphere occurs at leads in winter. As a result, a major salt input to the Arctic mixed layer is generated at these locations by brine rejection. Leads also constitute preferential melting locations in the early melting season, but their oceanography and climate relevance, if any, still remain unexplored during this period of the year. This study investigates the oceanographic circulation under a melted lead, resulting from the combined effect of the lead geometry, solar radiation and sea ice melting. Results derived from an idealized framework, suggest the daily generation of near surface convection cells that extend from the lead sides to the lead center. Convection cells disappear when melting is diminished during the period of minimum solar insolation. The cyclical generation and evolution of convection cells with the solar cycle, impacts the heat storage rate in the mixed layer below the lead. The contribution of this circulation pattern to the generation of the Near Surface Temperature Maximum (NSTM), is discussed in terms of its capability to inject warm surface waters below the open and sea ice surface. It has been suggested that the NSTM probably affects the oceanographic structure and acoustic properties of the upper ocean and the overlying ice cover.