Organic geochemistry of sediments from chemosynthetic communities, Gulf of Mexico slope

• Published in: Geo-marine letters 1994-06, Vol.14 (2-3), p.110-119
• Main Authors: Sassen, R., MacDonald, I. R., Requejo, A. G., Guinasso, N. L., Kennicutt, M. C., Sweet, S. T., Brooks, J. M.
• Format: Article
• Language: English
• Subjects: Marine
• ISSN: 0276-0460; 1432-1157
• DOI: 10.1007/BF01203722

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541-650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H sub(2)S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C sub(1)-C sub(5) hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C sub(1)-C sub(5) hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O sub(2) in sediments and triggers bacterial sulfate reduction to produce the H sub(2)S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C sub(1)-C sub(5) hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H sub(2)S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C sub(1)-C sub(5) concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C sub(1)) is present (8829 ppm).