Rising methane gas bubbles form massive hydrate layers at the seafloor

摘要: Extensive methane hydrate layers are formed in the near-surface sediments of Cascadia margin. An undissociated section such a layer was recovered at base gravity core (i.e. sediment depth 120 cm) southern summit Hydrate Ridge. As result salt exclusion during formation, associated pore waters show highly elevated chloride concentration 809 mM. In comparison, average background value is 543 mM. A simple transport-reaction model developed to reproduce Cl- observations and quantify processes as demand, fluid flow. From this first field observation positive anomaly, high formation rates (0.15–1.08 mol cm-2 a-1) were calculated. Our results also suggest that flow rate accretionary margin constrained 45–300 cm a-1. The amount needed build up enough produce observed enrichment exceeds solubility water. Thus, most gas likely from ascending bubbles rather than solely CH4 dissolved