Abstract:
The ocean influences climate by storing and transporting large amounts of heat and carbon, and exchanging these properties at the air-sea interface. The subduction of these properties from the ocean mixed layer to the interior is a key process for the regulation of the global climate. One way the ocean transports properties vertically and horizontally is through submesoscale (1-10 km. instabilities, which manifest in regions of large horizontal density gradients, of which the Southern Ocean is ubiquitous. This study investigates the impacts of submesoscale instabilities in the Subantarctic Zone using high-resolution (1-2 km, 2 hourly. autonomous glider observations collected over four full seasonal cycles (winter to summer.. Results indicate submesoscale instabilities propagate in winter and spring where Ertel potential vorticity suggests unstable flow. We show that winds orientated along the flow of fronts induce a destabilising flux via a horizontal Ekman buoyancy flux (EBF. towards the less dense domain of the front. EBF erodes the upper ocean stratification, deepens the mixed layer depth and reverses the sign of the potential vorticity, making the flow susceptible to submesoscale instabilities. Wind relaxation and when the wind orientation reversed against the frontal current restratified the mixed layer, enhancing the stratification and stabilising the flow. This restratifying flux is driven by the strength of the horizontal density gradients and the strength of the wind stress. When implemented into the 1-D PWP mixed layer model, EBF fluxes show upper ocean stratification to resemble our glider data, while 1-D air-sea fluxes over-estimate stratification. Previous work shows EBF is associated with turbulent fluxes, which may have key implications for mixing and vertical transport in the Southern Ocean. Therefore, this study shows the need to incorporate submesoscale processes into global climate models. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.
