Collaborative Proposal: Studies of Stirring and Mixing at the Submesoscale in the Ocean

The long term goal of the Scalable Lateral Mixing and Coherent Turbulence DRI, under which the PIs are funded, is to understand the processes that stir and mix tracers in the ocean on lateral scales of 100 kilometers to 10 meters, the so-called submesoscales. The specific long term goals of the PIs are to understand the influence of mesoscale strain in driving stirring and mixing at the submesoscale, and to develop a robust theoretical framework through which to interpret the observations. The objective of the DRI group is to devise and execute field experiments, supported by numerical simulations, that will distinguish between potential mechanisms of submesoscale stirring and mixing. The many interacting processes occurring at the submesoscales present a serious challenge to this effort. In order to focus the team work, potential mechanisms were distilled into three core hypotheses H1 Isopycnal mixing at scales of 10 m -10 km in the stratified ocean is the result of stirring by coherent vortices generated by mixing events associated with gravity wave breaking the so-called vortical modes H2 Isopycnal mixing at the submesoscale is effected by motions resulting from a cascade of tracer and potential vorticity PV variance from the deformation scale where baroclinic instability generates mesoscale eddies to smaller scales H3 Both diapycnal and isopycnal mixing in the upper ocean are enhanced by ageostrophic instabilities along lateral density fronts generated at the submesoscale.