Estimating Open Ocean Vertical Current Velocity from Glider Flight Characteristics: application to mixing processes in the Gulf of Mexico

Understanding the physical processes that control deep water mixing of the open ocean is fundamentally important to ventilation, carbon sequestration, and hurricane intensification research. The Loop Current and associated eddies are the most energetic meso-scale circulation features of the Gulf of Mexico. For this study, we estimate the vertical current velocity from anomalies in the vertical ascent and descent rates of two Slocum ocean buoyancy glider missions in the northern Gulf of Mexico in fall 2015. The vertical current velocity estimates are related to mixing processes of the open ocean. The gliders collected upper ocean (surface to 1000m; 1 Hz sampling, vertical and horizontal velocities ~20 cm/s) data, e.g., CTD, fluorometer, dissolved oxygen. During the ~80-day mission, the gliders transited multiple current features; analyses shows strong gradients and deepening of the Temperature, Salinity, and density isolines at the boundary of the Loop Current and warm core eddy structures. Vertical sections of estimated vertical water velocity shows coherent horizontal structure aligned with the density gradients at the base of the Loop Current velocity core and intensification between the eddies, likely the result of internal wave generation. Vertical and horizontal variability of Brunt-Vaisala (stability) frequency indicates enhanced vertical mixing in the upper 600 meters and marked contrasts between the slope waters, open ocean and at the periphery of eddies. Although satellite observations reveal the large scale presence of oceanic features, the glider-derived geostrophic velocities smaller spatial scale current structures on the periphery of the eddies that are not resolvable by satellite altimeter observations alone.