Breier

Plume Particle Aggregation and the Fate of Deep-Sea Hydrothermal Flux

J.A. Breier*¹, B. Toner², C.R. German³

Corresponding author: jbreier@whoi.edu
¹Woods Hole Oceanographic Institution, Applied Ocean Physics & Engineering, Woods Hole, MA 02536
²University of Minnesota – Twin Cities, Environmental Chemistry, St. Paul, MN 55108
³Woods Hole Oceanographic Institution, Geology & Geophysics, Woods Hole, MA 02543

We are using suspended hydrothermal plume samples to examine the fine scale (μm- and nm-range) mineralogical and biogeochemical composition of hydrothermal particulates. Past studies describe the basics of abiotic particle formation and estimate hydrothermal chemical discharge; but the actual fate of hydrothermal plume particles, dispersal and transformation in the water column and/or burial at the seafloor, remains poorly constrained. Our analyses of suspended plume particle samples from 9°50’ N EPR suggests that hydrothermal plume particle formation and transport is more complex than previously thought – and must involve biotic as well as abiotic processes. Our data show that a large fraction of 9°50’ N EPR plume particles are micro-aggregates of sulfur-rich organic carbon and iron-rich mineral phases. The composition and structure of these micro-aggregates is potentially very significant as it may mediate reactions with seawater and microbes, control particle buoyancy, and determine the ultimate fate (ocean dispersal vs. sediment burial) of hydrothermal flux. To progress, we need a more in-depth understanding of the key mechanistic elements of the abiotic and biotic particle-aggregate formation process: i) How does micro-aggregate structure arise? ii) At what stage, and in which phases, are trace elements and nutrients incorporated? and iii) How does particle aggregate structure and composition influence particle transport and oxidation? We present the working hypotheses we have developed for these processes based on our present data.

Keywords:
East Pacific Rise, Plume Chemistry, Microbial Processes, Particle Transport

Contributions to Integration and Synthesis:
Hydrothermal research would be significantly advanced through synthesis of this research with complementary research concerning microbial processes, host-rock geochemistry, and tectonic processes. Better understanding of plume particle formation will allow us to interpret data concerning water-column microbial activity. Better understanding of the relationship between plume particle chemistry and aggregation and host-rock geochemistry will allow us to estimate the net effect (i.e. input and scavenging vs. discharge) of sea-floor hydrothermal activity on ocean trace element chemistry. A better understanding of plume particle formation, dispersal, and preservation will inform interpretations, based on sediment trap and core samples, of changes in hydrothermal activity across tectonic/volcanic cycles – a fundamental aspect of deep-sea vent systems. Our data and modeling efforts are ready for integration with existing datasets of physical transport, sedimentation, and tectonic activity for 9°50’ N EPR. In addition, new rising plume geochemical and microbial samples, recently collected along the Eastern Lau Spreading Center (Kilo Moana, ABE, Tahi Moana, Mariner, and Tui Malila), are now available for a detailed investigation of the relationship between water column microbial activity and particle geochemistry. These samples provide an excellent opportunity to synthesize models of abiotic and biotic particle formation processes with models concerning host-rock and tectonic controls on vent-fluid geochemistry.