Using Continental Shelf Glider Data to Investigate the Relationship between Oxygen and Organic Material in the Marine Environment

Robert Iles, Texas A&M University, Department of Oceanography, College Station, TX, United States, Steven Francis DiMarco, Geochemical and Environmental Research Group (GERG), College Station, TX, United States, Anthony Knap, Texas A&M University, Geochemical and Environmental Research Group, College Station, United States and Nan D Walker, Louisiana State University, Baton Rouge, LA, United States; LSU-Coastal Studies Institute, Baton Rouge, LA, United States
Abstract:
Two buoyancy glider missions in the shallow waters of the Texas continental shelf reveal small spatial scale (~1 km) and short temporal scale (hours) variability of oxygen and organic material. Understanding the origin and fate of organic matter in the coastal zone of the northern Gulf of Mexico has broad scientific research and policy implications. Nutrients and organic matter fuel the processes that drive the large area of hypoxic water that occurs seasonally on the Texas-Louisiana shelf. In order to further our knowledge of the mechanisms controlling hypoxia, understanding the elements that regulate primary production and remineralization is essential. Contrary to usual methods of data collection at widely displaced discrete stations, gliders can provide near-continuous measurement of the total water column over a period of days to weeks.

The July 2015 glider data complement understanding of processes in this region by spatially and temporally resolving the structure and variability present on the shelf. A distinct diurnal pattern in dissolved oxygen concentration was observed, with concentrations varying at times greater than 1 mg L-1, at the same depths, from local noon to midnight. Additionally, observations of chromophoric dissolved organic matter (CDOM) and salinity, which are typically inversely related on the shelf, CDOM within a sub-mesoscale eddy was found to be constant throughout the water column and across the entire range of measured salinity. Within this eddy, the largest diurnal variations in oxygen were observed. CDOM/Salinity/oxygen relations indicate the presence of CDOM production across the shelf and at distances too far to have been advected from remote riverine sources.

Our observations demonstrate the extensive variability in biogeochemical processes in the northern Gulf of Mexico and underscore the importance of resolving sub-mesoscale variability beneath the surface as these can impact primary production and remineralization processes.