Enhanced Methane Oxidation Capacity of Cold Seep and Hydrothermal Plume Communities in the Gulf of California

Hannah Choi, Rachael Karns, Andrew Montgomery and Samantha B Joye, University of Georgia, Department of Marine Sciences, Athens, GA, United States
Abstract:
The Gulf of California is a unique ecosystem characterized by active hydrothermalism and petroleum generation. Fluid exchange between the deep subsurface and bottom waters occurs across the system; these fluids are injected into hypoxic bottom waters. We assessed biogeochemical signatures, microbial activity and microbial community composition in methane-rich hydrothermal plumes from Guaymas and Pescadero Basins and in gas plumes along the Sonora Margin. The microbial community in plumes reflects an amalgam of inputs from different end-members, which generates an inoculum to the plume. Conditions within the plume then select for species that are scarce or relatively inactive in their original habitats. Methane oxidation (MOx) rates within the hydrothermal plumes of Guaymas and Pescadero Basin are highly elevated compared to those of background waters. This increased activity demonstrates the ability of rare biosphere species to bloom when favorable conditions are encountered. Sonora Margin gas plume MOx rates, while also well above background, are not as high as the rates observed in hydrothermal plumes. Temperatures of hydrothermal plumes are slightly elevated over those in gas plumes (background temps are 2-3 ºC while plume temps can be over 5 ºC), but concentrations of methane, ammonium and trace metals are markedly higher in hydrothermal plumes. These differences in geochemistry increase the capacity of the microbial community to consume methane. A comparison of the metabolic rates and microbial communities at these three contrasting areas within the partially enclosed Gulf of California illustrates at the boom-and-bust lifestyle of deep sea aerobic methanotrophs and the persistence and dispersal of rare biosphere species in the marine environment.