Consideration of the biogeochemical implications for mesoscale instability driven cross front filaments in glider oxygen optode sensor data

During the pilot CALYPSO program in Spring 2018, repeated glider transects across the Almeria – Oran front monitored mesoscale instability at the frontal boundary between inflowing Atlantic waters and recirculating Mediterranean waters, for a period of ~ 6 weeks. Vertical perturbations in the frontal boundary are observed as a repeated ‘pumping’ like steepening and relaxation of the isopycnal surfaces across the front. We will present clear signals of highly oxygenated water descending underneath ascending, more weakly oxygenated water as the process of baroclinic instability at the front brings light Atlantic inflow waters of the eastern Alboran Gyre up and over denser recirculating Mediterranean waters. Baroclinic instability at the mesoscale creates 3D sub-mesoscale filamentary pathways along and across the front. The oxygenated filaments not only supply oxygen for the in-situ subducted micro-biological communities, which would not be available to gravitationally sinking particles; the process also provides a mechanism for the oxygenation of deeper layers of the water column through the increase of surface area available for turbulent mixing and diffusive processes. Conversely, the ascending filaments provide a mechanism for the “express” ventilation of weakly oxygenated deeper waters; also the potential for the supply of nutrients to the surface waters that could contribute to the enhancement of the phytoplankton biomass. These vertical pathways play also a key role in setting both the vertical and cross-front distribution of the marine microbial community. By comparison with previous published work quantifying filamentary and eddy transports, and concurrent diagnoses in the CALYPSO pilot study, we will make an assessment of the potential for increased oxygen utilization through these cross frontal and vertical pathways created by the physical requirement to conserve potential vorticity whilst releasing potential energy during instability processes.