Biophysical Evidence of Subduction at Submesoscales

The vertical exchange of water between the mixed layer and ocean interior is enhanced at ocean fronts by submesoscale instabilities, that are well represented in ocean models, but difficult to observe in the ocean. We seek observational evidence for vertical exchange by identifying anomalies in water mass properties, and biological tracers that are modified on times scales of days to weeks. Observations along a strong density front in the Western Mediterranean Sea are analyzed to identify intrusions of surface mixed layer water within the pycnocline. The impact of these features on vertical transport is estimated by integrating a wide range of in situ observations collected on two cruises conducted in the Western Mediterranean in 2018 and 2019, as part of the CALYPSO campaign. Measurements collected from towed, Lagrangian, and ship-based platforms are combined to investigate the three-dimensional pathways connecting the surface layer to the ocean interior, and to infer vertical exchange rates.