title: Mercury concentrations, speciation, and isotopic composition in sediment from a cold seep in the northern Gulf of Mexico.
abstract: Total-Hg, monomethylmercury (MMHg), and mercury isotopic composition was determined in sediment from a cold seep and background sites in the northern Gulf of Mexico (nGoM). Total-Hg averaged 50 ng/g (n=28), ranged from 31 to 67 ng/g, and decreased with depth (0-15 cm). MMHg averaged 0.91 ng/g (n=18), and ranged from 0.2 to 1.9 ng/g. There was no significant difference for total-Hg or MMHg between cold seep and background sites. δ(202)Hg ranged from -0.5 to -0.8‰ and becomes more negative with depth (r=0.989). Mass independent fractionation (Δ(199)Hg) was small but consistently positive (0.04-0.12‰); there was no difference between cold seeps (Δ(199)Hg = +0.09±0.03; n=7, 1SD) and background sites (Δ(199)Hg=+0.07±0.02; n=5, 1SD). This suggests that releases of hydrocarbons at the cold seep do not significantly alter Hg levels, and that cold seeps are likely not major sources of MMHg to nGoM waters.
authors.affiliation: Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA.
authors.forename: Garry
authors.initials: G
authors.lastname: Brown
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sleeper
authors.forename: Marcus W
authors.initials: MW
authors.lastname: Johnson
authors.forename: Joel D
authors.initials: JD
authors.lastname: Blum
authors.forename: James V
authors.initials: JV
authors.lastname: Cizdziel
mesh_terms: D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry*; D060851:Gulf of America; D008628:Mercury / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Cold seep; Gulf of Mexico; Isotopic composition; Mercury; Methylmercury; Sediment