Glider Observations of the Loop Current and LC Eddy in the western Gulf of Mexico: comparison of buoyancy mixing and relationships with oxygen variability

The loop current and loop current eddies highly dominate the oceanographic system of the Gulf of Mexico. Even though it is a most dominant feature, the controlling mechanism and it affects physical, chemical, and biological properties yet totally understood. For this study, two simultaneous 90-day Slocum Glider missions was carried out in the northern Gulf of Mexico in fall 2015. During this mission, the gliders fly-through multiple current features and collected upper ocean (surface to 1000m) oceanographic data, e.g., CTD, fluorometer, dissolved oxygen. Analysis of Glider data shows the deepening of the Temperature, Salinity, and density isolines inside the loop current and warm core eddie structures. Brunt–Väisälä frequency calculated using glider data and T-S plots indicates vertical mixing in the upper 600 meters of the loop current and marked contrasts between the slope waters of the slope, the periphery and internally to the eddies. Satellite observation, as well as calculated geostrophic velocity, reveals the presence of a sub-meso current structure on the periphery of the eddie features that are not resolvable in the available satellite altimeter products. This suggests fine scale variability and processes important to mixing and for operational performance of the glider. Dissolved oxygen distributions and vertical structure show the importance of ventilation processes in maintaining the range and thickness of the Oxygen Minimum Zone in the Gulf of Mexico (at 300 to 600 m), which is associated with transport of Antarctic Intermediate water within the western boundary system of the Atlantic Ocean. In the upper surface waters (50-100 m), the oxygen concentration is influenced by presence (or absence) of phytoplankton biomass and proximity to Caribbean sourced waters.