Biogeochemical patterns and processes in buoyant, deep-sea hydrothermal plumes

Abstract

Along the global mid-ocean ridge, sub-seafloor hydrothermal circulation results in the exchange of heat and chemical species between seawater and the ocean crust. The resulting thermally and geochemically altered fluids are vented at the seafloor. The mixing of cold, oxic deep-ocean waters with hydrothermal fluids creates plumes with physically and chemically dynamic features. Hydrothermal plumes represent a globally distributed interface where marine hydrothermal circulation exerts its biogeochemical influence on elemental budgets of ocean basins. The goal of the present study is to describe the microbiological niches created by physical and geochemical gradients in plumes. One of our central hypotheses is that microorganisms respond to and alter the geochemistry of hydrothermal plumes. To achieve this goal and test our hypothesis, a field study was undertaken at the Eastern Lau Spreading Center (ELSC). While multiple vent sites along the ELSC are included in the larger study, here we report on an integrated, biogeochemical investigation of a single buoyant plume within ABE vent field. A series of replicate sample sets were collected by in situ filtration at 0.5m, 40m, 200m within a buoyant plume using the ROV JASON. Above plume background and near bottom background sample sets were also collected. Hydrothermal plume particles in sample replicates or splits have been queried for bulk geochemistry, particle-by-particle mineralogy, and microbial community composition. These three data streams are being evaluated individually to characterize the geochemical and microbiological changes throughout the plume with respect to above and below plume backgrounds. In addition, an iterative and integrated analysis is being used to compare: (1) calculated mineralogy to direct measurements; and (2) predicted energy yields from chemoautotrophy to observed microbial composition.