Temporal and spatial variability in the Endeavour Ridge neutrally buoyant hydrothermal plume: Patterns, forcing mechanisms and biogeochemical implications

Time series records of horizontal current velocity, temperature, light attenuation and settling particle flux obtained using moored instruments above Endeavour Ridge in the northeast Pacific Ocean elucidate the dynamics of a deep-sea, neutrally buoyant, hydrothermal plume. Data collected in four mooring deployments over three years within 20 km of an active hydrothermal vent field quantify heretofore suspected temporal and spatial variability in the plume, and provide evidence of causality. Over time scales of hours to days, local fluctuations in temperature and suspended particle concentration primarily reflect horizontal transport of hydrothermal effluent by currents. However, it is dramatic variability in lateral transport of hydrothermal material over longer time scales (months to years) which profoundly influences the spatial distribution of settling particle flux. Steering of the hydrothermal plume by horizontal currents, in concert with seasonal effects linked to production of biogenic particulate material in the upper ocean, together explain the predominant temporal patterns in settling hydrothermal particle flux measured within and beneath the plume. Spatial variability in plume-guiding currents is also pronounced; horizontal flow is non-uniform over distances of ;Despite the potential complexity of both the physical oceanographic regime and the effects of multiple particle-transformation processes, the changes in settling flux of hydrothermal elements as a function of along-plume distance can be described by a simple model that includes first-order loss of particle flux and along-plume horizontal advection. An innovative technique employing probability density functions of horizontal flow direction is used to scale measured sediment-trap fluxes to reflect true beneath-plume fluxes of hydrothermal elements. These scaled settling particle fluxes are used to define the functionality of settling hydrothermal particle flux with distance from the vent-field, predict the settling flux of specific elements directly above the vent field, and calculate the integrated settling particle flux of hydrothermal elements within...