Geochemistry of reduced fluids from shallow cold vents hosting chemosynthetic communities (Comau Fjord, Chilean Patagonia 42 degrees S)

摘要

Reduced fluids from shallow-marine vents sustain chemosynthetic bacterial mats located at the base of the volcano Barranco Colorado in Comau Fjord (X-Huinay; 42 23.279'S, 72 27.635'W). We characterized the chemical environment in which these bacteria thrive. To this end, we analyzed CH4, Eii2s, 02, DIC, and stable isotopes (813C, 52H and 8180) and compared them with readings taken at a control station (which lacks evidence of fluid venting and mat-forming bacteria). In addition, CI'D measurements, chlorophyll-a, and nutrient analyses were performed. At depths of approximately 5-7 m, the water column exhibited a pycnocline that formed under the influence of fresh water discharges, especially during the summer season, which also affected the surface temperature. Bacterial mats and elemental sulfur flocs were observed in the vicinity of the vents (X-Huinay station), and higher concentrations of reduced compounds (CH4 and H2S) were found in the vent fluids, in particular at a depth of 36 m. No significant differences in the temperatures of vent and ambient waters were detected. The bottom water close to the vents possessed notably low concentrations of reduced compounds, indicating a rapid and large-quantity dilution of the chemicals from vents. The surface water featured light isotopic values of 82H and 180 due to the freshwater input from melting ice and precipitation. A linear mixing trend was observed between the freshwater (negative isotopic values) and the fjord bottom water (positive values) that was not influenced by vent fluid. This trend suggests that the venting water corresponds to the mixing among local meteoric water, spring water, and seawater. This result is relevant to understanding how freshwater and meteoric water influence the chemical composition of seawater and how this mixing could impact the marine biota in the vicinities of the vents. (C) 2014 Elsevier Ltd. All rights reserved.