Mercury concentrations, speciation, and isotopic composition in sediment from a cold seep in the northern Gulf of Mexico.

Highlights: [•] T-Hg, MMHg, and Hg isotopes were determined in Gulf of Mexico deep marine sediments. [•] Levels of mass independent fractionation of Hg isotopes varied from coastal sediments. [•] Levels of the MMHg were only slightly elevated at the cold seep site. [•] Cold seeps do not appear to be significant sources of MMHg to Gulf of Mexico waters. [ABSTRACT FROM AUTHOR]