Using an Autonomous Biogeochemical Profiling Float to Determine the Effect of Natural Hydrocarbon Seeps and a Tropical Depression on the Gulf of Mexico System

The Northern Gulf of Mexico (NGOM) is a semi-enclosed sea influenced by the Loop Current, Mississippi River Plume, and many natural hydrocarbon seeps. Several biogeochemical APEX (BGC-APEX) profiling floats have been deployed in this region over the past few years. Our study focuses on data collected by Hydro-Optical Biogeochemical Observer (HOBO), a BGC-APEX float equipped with a CTD, chlorophyll fluorometer, four channel radiometer (to measure downwelling irradiance and upwelling radiance at 412, 443, 490, and 555 nm), and sensors for particulate backscatter and oxygen. The float was deployed twice in June-July 2015 and profiled the water column from 500m to the surface about every 4.5 hours. The first deployment lasted 12 days and produced 62 profiles over a span of 195 km, while the second deployment lasted 8 days, collecting 37 profiles over 160 km. The water column chlorophyll fluorescence data were analyzed to investigate changes in phytoplankton biomass during the two deployments accounting for differences arising from varying light levels and near-inertial oscillation. The influence of natural hydrocarbon seeps and a tropical depression with windspeeds in excess of 40 knots on the phytoplankton distribution in the water column will be presented. In the two days preceding the depression the average sea surface salinity and depth of the deep chlorophyll max were 36.37±0.07ppt and 88.89±11.64m while in the following two days they changed significantly to 36.05±0.04ppt and 81.30±4.11m. Data collected by the float will also be compared to ocean color satellite data.