This dataset contains CTD, water quality and particle and zooplankton sample elemental (total C and N, C/N ratio) and isotopic (delta 13C, delta 15N) data collected during R/V Endeavor cruise EN496 in the northern Gulf of Mexico from 2011-07-03 to 2011-07-26. Particle and zooplankton samples were collected during cruise EN496 using a CTD-rosette and a MOCNESS. The objectives were to collect water column and benthic samples in the vicinity of the Mississippi River Plume, as well as, at/near active seeps. Elemental and isotopic data were collected at 18 stations, while CTD profiles were done at 51 locations. Elemental and isotopic data includes the delta 13C and 15N, total Nitrogen and Carbon and the C/N ratio. Hydrographic data was collected using a Sea-Bird SBE-9 and the data includes temperature, salinity, oxygen concentration, sound velocity, beam attenuation and transmission, sea level, Photosynthetically Active Radiation (PAR), fluorescence and surface irradiance.