Geochemistry of dissolved gases in the hypersaline Orca Basin /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1980.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Hypersaline, anoxic waters significantly affect the biogeochemistry of dissolved gases in the Orca Basin (northern Gulf of Mexico). The high stability of the Orca brine pool makes it an ideal laboratory for studying production and consumption of dissolved gases during anaerobic decomposition. Depth distributions were determined for nitrogen, oxygen, argon, methane, ethane, propane, ammonia, hydrogen sulfide, and nitrous oxide. Physical stratification of the water column strongly influences Orca Basin gas distributions. The high salinity brine ([about] 250 0/00) is internally well mixed due to convective overturning, but transfer across the brine-sea water interface is controlled by molecular diffusion. With a molecular diffusivity of 10^-5 cm^2*sec^-1 it will take 10^6 years for all salts to diffuse from the basin. Heat diffuses faster than salt and is lost from the basin at a rate of 0.5 μcal*cm^2*sec^-1. If geothermal heat input from the sediments is slightly higher, this input could account for the higher temperature in the brine (5.6°C) compared to the deep Gulf waters (4.2°C). The high stability of the brine (due to increased density) prevents either reactants or products of anaerobic decomposition from escaping by other than molecular processes. Concentrations of biogenic methane and ethane are higher there than in any other anoxic marine basin. Oxygen, nitrate, and nitrous oxide are absent from the brine, while phosphate and ammonia levels are 60 and 500 μmol*liter^-1, respectively. However, there is no hydrogen sulfide in the anoxic brine. Rates of microbial activity are generally slower in the hypersaline Orca Basin. Organic matter is decomposed so slowly that fronds of Sargassum seaweed have been found buried at depths of 5 m in the sediment, the only sedimentary environment where this has been observed. The absence of free sulfide can be attributed to a slower rate of sulfate reduction. Not enough sulfide is being generated to complex the iron produced there. Iron has accumulated to levels of 30 μmol*liter^-1 in the brine and only metastable iron sulfides, not pyrite, are found in the sediments... |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Oceanography." |
| Physical Description: | xvii, 265 leaves : illustrations, maps, graphs ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 250-264). |