Plume dispersed hydrothermal particles: A time-series record of settling flux from the Endeavour Ridge using moored sensors

Abstract

Settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast Pacific Ocean provide information about the deep-sea distribution of hydrothermal material. Results of an 8-day, near-field, single-trap experiment and a 340-day, multi-instrument, 5-trap deployment two kilometers from the Endeavour Ridge vent field show variability in the quantity and composition of the plume-to-sediment particle flux over time, with depth, and with distance from the vent field. Hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment; a factor of three variation in Fe/S among these periods reflects temporal changes in phase composition. Changes in flux with depth—for example, a 200-fold increase in Cu and Zn between above- and below-plume traps are evidence of hydrothermal input. Comparison of fluxes determined in the near- and far-field experiments reveals the spatial influence of vent effluent. Near-field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in Fe, Cu, and organic carbon, but depleted in Mn. Calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field. Interpretation of elemental, mineralogical, and grain-size analyses suggest that chemical precipitation kinetics, other physical and biological particle-forming processes, changes in vent output, and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations. Our findings suggest that these rate-interdependent processes be included in realistic models of hydrothermal particle flux.