Thermal vs. Haline Drivers of Restratification in the Labrador Sea

The Labrador Sea is a vital component of global ocean circulation, hosting vigorous deep convection that can mix to deeper than 2,000 m. Features that drive convection are widely studied, but a lack of high-resolution, in situ observations hinder our understanding of how finescale dynamics influence the convective process and trigger restratification in spring, particularly at the submesoscales (< ~ 10 km). This study assesses contributions of temperature and salinity to both vertical and horizontal stratifications during early winter, convection, and spring restratification, using data collected by five underwater gliders deployed in the winters of 2019/20 and 2021/22. Using the Turner angle, we show that vertical stratification in the Labrador Sea shifts from salinity-stratified in early winter to temperature-unstable during convection, and back to salinity-stratified in the early restratification period. Horizontally, both warm and fresh intrusions drive lateral density anomalies during restratification, with the haline influence dominating. Wavelet analysis of these anomalies illustrates increased submesoscale activity during restratification, and comparisons of thermohaline contributions show the predominance of salinity-driven submesoscale fronts. These fronts have the potential to rapidly stratify the water column, and evidence the importance of freshwater intrusions at submesoscales in halting convection.