Séminaire
While often conceptualized in a spatially- and/or temporally-averaged sense, significant mixed layer depth variability occurs on both seasonal and much shorter timescales. I will present two methods of studying this variability and discuss the implications of this work for understanding the dynamics of the Southern Ocean in particular. 3-dimensional Lagrangian upwelling pathways are studied using an ocean general circulation model. Virtual drifters are released around the Southern Ocean and tracked as they were advected forward in time. The pathways are used to study outcropping and water mass modification statistics, both of which have implications for the role that the ocean plays in setting global climate. A strong localization of upwelling sites is found, with 59% of virtual drifters outcropping in the Pacific basin or Drake Passage. Furthermore, the mixed layer residence time is found to be very short when compared to typical gas exchange timescales (a mean of 30 days for any given outcropping event), suggesting a disequilibrium between the atmosphere and waters subducted from the mixed layer.
In the second study, Seaglider observations from the Southern Ocean are used to study mixed layer dynamics in Drake Passage. Glider profiles are combined with ECMWF reanalysis winds and surface fluxes to determine the strength and types of submesoscale instabilities found in the mixed layer. Both Ekman buoyancy fluxes and baroclinic mixed layer instability are found to be prevalent in the region, especially downstream of major topographic features. This work demonstrates the persistence of submesoscale activity throughout the summer months and points to a need for better parameterizations of these dynamics in ocean modeling.