TY - JOUR
T1 - Dissolved and particulate Fe in a hydrothermal plume at 9°45'N, East Pacific Rise
T2 - Slow Fe (II) oxidation kinetics in Pacific plumes
AU - Field, M. Paul
AU - Sherrell, Robert M.
N1 - Funding Information:
The authors acknowledge Greg Ravizza and Linda Godfrey for their superb efforts in obtaining the 1997 samples and for intellectual contributions. We received able shipboard assistance of Laura Magde, Kathy Sullivan, and the Captain and crew of the R/V Atlantis II and the Alvin Group. We are grateful to Dan Fornari and Sandy Williams for the loan of the CTD and transmissometer. Karen Von Damm, Gary Massoth, Frank Millero, Chris Sabine, Clare Reimers, and Peter Rona were generous in providing supporting data and expertise. Tom Lill and Jingfeng Wu assisted with pH calculations and DFe analysis, respectively. We are grateful to Harry Elderfield and Chris German for their very helpful reviews. This work was supported by NSF awards OCE 9217193 and OCE 9601668 to RMS.
PY - 2000/2
Y1 - 2000/2
N2 - Production of Fe(III) particles in hydrothermal plumes is of fundamental importance to the long-term effect of hydrothermal circulation on seawater composition. To elucidate the fundamental controls on Fe redox kinetics and solution/particle partitioning in neutrally buoyant plumes, we sampled near-field (<3 km) plume particles at 9°45'N on the East Pacific Rise in 1996, returning in 1997 to sample both particulate and dissolved phases (0.40 μm filter). Concentrations of dissolved Fe varied from 320 to 20 nM in proximal (<0.3 km from vent site) to distal samples (1-3 km downfield), constituting ˜85-50% of total Fe, respectively. Based on vent fluid dilution factors calculated from dissolved Mn, a mass balance for vent fluid Fe at this site indicates that ˜65% of Fe is lost to particulate sulfide settling in the buoyant plume, and that particulate Fe in distal (1-3 km) samples is twice as concentrated as predicted from dilution of particles in proximal plume water. These observations are consistent with a calculated Fe(II) oxidation half-time of 3.3 h, long enough that Fe(III) colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions, preventing generation of high particulate Fe concentrations (11-56 nM observed). A general investigation of Fe(II) oxidation rates in plumes worldwide gives Fe(II) oxidation half-lives as short as 17 min at some Atlantic sites, and as long as 6 h at some Pacific sites. The calculations indicate that the distribution of Fe particles in plumes depends chiefly on inter-basin differences in ambient deep water chemistry (primarily pH and dissolved O2) and on local currents driving plume dilution, and to a much lesser extent on variations in primary vent fluid composition. Long-term changes in thermohaline circulation or ocean biogeochemistry may therefore alter Fe dynamics and minor element fluxes associated with global hydrothermal activity, independent of variations in crustal production rates.
AB - Production of Fe(III) particles in hydrothermal plumes is of fundamental importance to the long-term effect of hydrothermal circulation on seawater composition. To elucidate the fundamental controls on Fe redox kinetics and solution/particle partitioning in neutrally buoyant plumes, we sampled near-field (<3 km) plume particles at 9°45'N on the East Pacific Rise in 1996, returning in 1997 to sample both particulate and dissolved phases (0.40 μm filter). Concentrations of dissolved Fe varied from 320 to 20 nM in proximal (<0.3 km from vent site) to distal samples (1-3 km downfield), constituting ˜85-50% of total Fe, respectively. Based on vent fluid dilution factors calculated from dissolved Mn, a mass balance for vent fluid Fe at this site indicates that ˜65% of Fe is lost to particulate sulfide settling in the buoyant plume, and that particulate Fe in distal (1-3 km) samples is twice as concentrated as predicted from dilution of particles in proximal plume water. These observations are consistent with a calculated Fe(II) oxidation half-time of 3.3 h, long enough that Fe(III) colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions, preventing generation of high particulate Fe concentrations (11-56 nM observed). A general investigation of Fe(II) oxidation rates in plumes worldwide gives Fe(II) oxidation half-lives as short as 17 min at some Atlantic sites, and as long as 6 h at some Pacific sites. The calculations indicate that the distribution of Fe particles in plumes depends chiefly on inter-basin differences in ambient deep water chemistry (primarily pH and dissolved O2) and on local currents driving plume dilution, and to a much lesser extent on variations in primary vent fluid composition. Long-term changes in thermohaline circulation or ocean biogeochemistry may therefore alter Fe dynamics and minor element fluxes associated with global hydrothermal activity, independent of variations in crustal production rates.
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U2 - 10.1016/S0016-7037(99)00333-6
DO - 10.1016/S0016-7037(99)00333-6
M3 - Article
AN - SCOPUS:0034004734
SN - 0016-7037
VL - 64
SP - 619
EP - 628
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 4
ER -