Surface warming in a coastal current during spring time stratification

Abstract

<p>The winter hydrography of the Scotian Shelf predominantly consists of warm and salty continental slope water, wedged under<br>the cool and fresher water of a coastal current. The frontal zone between these water masses is associated with subduction and submesoscale lateral mixing processes. Previous studies have shown that in springtime a transition occurs in which the mixed layer stratifies around a cold intermediate layer. The onset of the spring bloom typically occurs before significant surface restratification has taken <br>place, thereby contradicting the critical depth hypothesis.<br>A monthlong survey of repeat transects with several diving and surface gliders across the Scotian shelf was conducted <br>between March and April 2021. During several days of exceptionally calm and sunny conditions vertical profiles of micro-structure temperature, <br>and turbulent kinetic energy dissipation rates were obtained. <br>A surface warm layer was observed to develop and persist within the upper 10m, as a result of the strong insolation and <br>low wind forcing. The use of an autonomous upward microstructure profiler allows us to study the evolution of this layer in detail. <br>The profile data are used to estimate vertical heat fluxes at the surface and bottom of the mixed layer, which contribute to the springtime restratification.<br>We investigate the impact of surface restratification and frontal processes on both the heat budget of the mixed layer, and the export of particulate organic carbon to deeper layers during the spring bloom. The results of this survey help improve our understanding of heat and carbon transfer on the Scotian Shelf.</p>