Abstract:

Subtropical fronts are key regions in the world’s oceans as they provide the connection between the dynamically and biogeochemically different subpolar and subtropical oceans. Understanding the mechanisms that modulate the exchange of properties between these regions is not only locally important but may also help explain long-term changes that affect the climate system and may be sensitive to such exchanges. In this study, focus is given to the importance of submesoscale processes in triggering phytoplankton blooms at the subtropical front in the South Atlantic Ocean. A basin-wide model configuration is nested with a higher resolution domain within the frontal region in order to study the exchange of physical properties as well biologically active tracers. On average, a stronger zonal baroclinic jet is observed in the high-resolution domain. Frontal instabilities generated by imbalances in the thermal wind induce rapid changes in the mixed layer depth and generates more episodic blooms with slightly larger biomass during periods when surface stratification is increased. Nonlinearities associated with the Ekman dynamics seem to be responsible for the generation of large vertical velocities and are more important in the high-resolution domain because of larger gradients in relative vorticity.