Eddy kinetic energy and energy conversion rates along the Atlantic Water boundary current north of Svalbard

Abstract

Abstract. On the continental slope north of Svalbard, the boundary current carrying Atlantic Water (AW) loses heat as it flows eastward. This cooling cannot be fully attributed to atmospheric heat loss or turbulent mixing. Lateral exchange, potentially linked to mesoscale activity, has previously been proposed as a contributing factor, based on limited observations of eddies. Here, we analyse a year-long dataset of hydrography and velocity observations from two mooring arrays, supplemented by output from an eddy-resolving ocean model, to quantify the seasonal variability of eddy kinetic energy (EKE) and baroclinic and barotropic energy conversion rates over time-scales from days to months. Both EKE and conversion rates peak in autumn and winter, coinciding with the strongest boundary current and the warmest AW. Local EKE variability, however, is only weakly associated with conversion rates, suggesting advection from upstream generation sites or unresolved variability from limited measurements. Conversion is mainly baroclinic, through boundary current instability, providing conditions favourable for offshore propagation of warm-core eddies. Modelled conversion rates have a complex spatial structure with substantial values on the offshore, deeper side of the boundary current with comparable contributions from baroclinic and barotropic processes. Resulting mesoscale activity enhances lateral stirring and heat loss from the boundary current, particularly in winter and spring, contributing to the along-stream cooling of AW.