Abstract
In the sea ice-impacted Southern Ocean, the spring melt of sea ice
modifies the upper ocean. These modified waters subduct and enter the
global overturning circulation. Submesoscale processes act to modulate
the stratification of the mixed layer and therefore mixed layer
properties. Sparse observations mean that the role of submesoscales in
exchange across the base of the mixed layer in this region is not well
constrained. The goal of this study is to determine the interplay
between sea ice melt, surface boundary layer forcing, and submesoscale
flows in regulating the mixed layer structure in the Antarctic Marginal
Ice Zone. High-resolution observations suggest that fine-scale lateral
fronts, representative of submesoscale mixed layer eddies (MLEs), arise
from mesoscale gradients produced by northwards advecting sea ice
meltwater. The strong salinity-driven stratification at the base of the
mixed layer confined the MLEs to the upper ocean, limiting submesoscale
vertical fluxes across the mixed layer base. This strong stratification
prevents the local subduction by submesoscale flow of these modified
waters, suggesting that the subduction site that links to the global
overturning circulation does not correspond with the location of sea ice
melt. However, the presence of MLEs enhanced the magnitude of lateral
gradients through stirring and increased the potential for Ekman-driven
cross-frontal flow to modulate the stability of the mixed layer and
mixed layer properties. The inclusion, particularly of submesoscale
Ekman Buoyancy Flux parameterizations, in coupled-climate models, may
improve the representation of mixed layer heat and freshwater transport
in the ice-impacted Southern Ocean during summer.