While gross hydrothermal fluxes entering the ocean are known to be significant, much remains unknown about the fate of this material as it disperses through the oceans, and its impact upon ocean biogeochemistry. Mineral precipitation within hydrothermal plumes removes hydrothermally-sourced metals from solution and also acts to scavenge trace elements from the surrounding water column. Here, we investigate the fate of particulate Fe released from high-temperature hydrothermal venting at EPR 9°50′N and its potential impact on local deep-ocean Fe-isotopic and geochemical budgets. We measured the geochemical composition, mineralogy and Fe isotope systematics of hydrothermal plume products in order to determine whether mineral precipitation imposes characteristic Fe-isotope “fingerprints” for hydrothermally sourced Fe in the deep ocean. Our sampling includes sediment trap deployments after the eruptive event of Jan. 2006, allowing the examination of temporal changes of hydrothermal fluxes over a 160 day period. Results show that Fe isotope composition in the high-temperature vent fluids is rather constant over the sampling period 2004–2008, and that secular variations of δ56Fe values of plume particles from − 0.03 to − 0.91‰ (relative to IRMM-14 standard) could be explained by local processes leading to variable mixing extents of hydrothermal, biogenic and lithogenic particles. Through geochemical modeling, we have calculated the relative abundances of hydrothermal plume components such as sulfides, Fe oxyhydroxides, organic matter, biogenic and lithogenic phases. We demonstrate that Fe isotope fractionation in the hydrothermal plume occurs during the formation and rapid settling of Fe-sulfides that are characterized by δ56Fe values ranging from − 0.73 ± 0.13‰ to − 0.86 ± 0.13‰, which is systematically lower than the end-member hydrothermal fluids (δ56Fe = − 0.4‰). This study suggests that both the initial Fe isotope composition of the high-temperature vent fluids and its initial Fe/H2S ratio (i.e. Fe-sulfide precipitation versus Fe-oxyhydroxide precipitation) should impose characteristic Fe isotope “fingerprints” for hydrothermally derived Fe in the deep ocean.
Bibliographical noteFunding Information:
We thank Diane Adams and Lauren Mullineaux for sediment trap deployments at the EPR and Bill Seyfried for providing hydrothermal fluid samples from the oceanographic cruise AT-15. Support for sediment trap analysis was funded by OCE - 0647948 , awarded to CRG and OJR. We thank Maureen Auro for laboratory assistance at WHOI, Lary Ball and Emmanuel Ponzevera for daily maintenance of the MC-ICPMS and Yoan Germain for help with hydrothermal fluid analysis. We thank Bill Seyfried and Andrea Thurnherr for their helpful comments on the manuscript. Financial support for this work was also provided by the Labex Mer ( ANR-10-LABX-19-01 ), Europole Mer and FP7 ( #247837 ) grants to OJR. We thank M.A. Marcus for research support at the Advanced Light Source beamline 10.3.2. The Advanced Light Source is supported by the Office of Science, Basic Energy Sciences, Division of Materials Science of the U.S. Department of Energy ( DE-AC02-05CH11231 ).
© 2016 Elsevier B.V.
- Hydrothermal plume
- Iron isotopes
- Marine particles
- Mid-ocean ridges
- Seafloor hydrothermal systems
- Sediment traps