Water column anomalies associated with hydrothermal activity in the Guaymas Basin,Gulf of California |
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| Authors: | Andrew C Campbell Joris M Gieskes |
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| Institution: | Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093U.S.A. |
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| Abstract: | Sea floor hydrothermal activity in the Guaymas Basin, Gulf of California, is quite different from that associated with ridge crest spreading centers. Injection of hydrothermal fluids occurs in the bottom of a semi-enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean. In the Guaymas Basin the hydrothermal venting generates large clouds of fine suspended particulate matter (SPM) 100–300 m above active mounds and chimneys. These hydrothermal clouds have potential temperature anomalies of about 0.010–0.020°C, are enriched in dissolved silica, particulate manganese, and depleted in dissolved oxygen relative to areas away from the vents. The particulate manganese values increase from about 3 nmol/kg at ～ 1000 m, well above the enclosing topography of the subsill basin, to 100–150 nmol/kg in the clouds of SPM and in the bottom nepheloid layer. The particulate Mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved Mn2+ injected by the vents and entrainment of Mn-rich SPM in the rising hydrothermal plumes. Injection of silica-rich vent fluids into the basin bottom waters produces a silica anomaly of 10–15 μmol relative to the other deep basins of the Gulf of California. Spillover of Guaymas Basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the Gulf. A simple two-endmember mixing model indicates that the deep waters of the Guaymas Basin contain approximately 0.1% hydrothermal fluid. Oxygen anomalies associated with the hydrothermal clouds are on the order of 5 μmol relative to regions away from active vents. The basin as a whole shows a depletion in oxygen of about 13 μmol relative to the other deep basins of the Gulf. The mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents. Box models of the deep basins of the southern Gulf of California indicate that the Guaymas Basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins. The calculated flux of hydrothermal fluids into the Guaymas Basin is 10–12 m3/s. |
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