Arctic ocean submesoscale brine driven eddies: modeling of a sea ice edge front

Characteristic features of the wintertime Arctic Ocean are narrow and elongated fractures in the sea ice cover, up to hundreds of kilometers long and up to tens of kilometers wide, called leads. Leads expose the ocean to the cold atmosphere, establishing air-sea heat fluxes which freeze the oceanic surface. During new sea ice formation, dense and salt-enriched plumes of brine are rejected into the oceanic mixed-layer. Due to brine rejection, lateral density gradients appear at sea ice edges, creating fronts. Fronts store potential energy and are subjected to gravitational overturning. The effect of Earth's rotation prevents the complete slumping establishing along sea sea ice edge currents in a geostrophic balance state, known as geostrophic adjustment, leaving the isopycnals tilted. Baroclinic instabilities develop and grow into submesoscale eddies - typical vortical coherent structures of the oceanic mixed-layer. Transferring momentum and tracer properties laterally, submesoscale eddies are the leading order process of mixed-layer restratification. Current global climate models can not resolve this small scale turbulence and Arctic Ocean observations are limited due to the presence of sea ice. High resolution numerical models are therefore a powerful tool for investigating these unknown processes. In this work, idealized high resolution model experiments are setup in order to study the wintertime refreezing of an open ocean area near a sea ice edge. The results confirm that submesoscale eddies enhance the mixed-layer restratification subtracting energy from the mean flow and increasing the turbulent kinetic energy. Through the study of lateral density transfer scaling rate, a departure from the deformation radius emerges in geostrophic adjustment experiments and more strongly under ageostrophy predominance. The presence of an ageostrophic diffusion process can explain the frontal region widening.