HR: 1330h
AN: B12A-0750    [PDF]
TI: Measuring pH(in-situ) of hydrothermal fluids at Mid-ocean ridges: Main Endeavour Field(JDF); EPR 21§N, 9-10§N; Galapagos Rift
AU: * Ding, K
EM: mlcd@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AU: Seyfried, W E
EM: wes@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AU: Tivey, M K
EM: mktivey@whoi.edu
AF: Woods Hole Oceanographic Institution, 93 Water Street, Woods Hole, MA 02543 United States
AU: Von Damm, K L
EM: kvd@eos.sr.unh.edu
AF: Complex System Research Center, University of New Hampshire, 39 College Rd., Durham, NH 03824 United States
AU: Bradley, A M
EM: abradley@whoi.edu
AF: Woods Hole Oceanographic Institution, 93 Water Street, Woods Hole, MA 02543 United States
AU: Zhang, Z
EM: zhang125@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AB: The in situ pH measurements of seafloor vent fluids were conducted using a newly developed solid-state sensor. Measurements were made during a series of dives with DSV Alvin at the Main Endeavour Field (MEF, Juan de Fuca Ridge), East Pacific Rise (EPR) at 21$\deg$N, EPR at 9-10$\deg$N, and at the Galapagos Rift. Vent fluid temperatures and pressures ranged from 22 to 380$\deg$C and 220 to 250 bars (2200 to 2500 meters depth), respectively. The pH of the highest temperature fluid is only slightly acidic (5.1-5.4), instead of being at least a full unit lower as often measured at the room condition from fluid sample. However, our in-situ pH results are at the same magnitude with theoretically predicted in-situ values from the room condition measurement. Dramatic pH lowering is observed during vent fluid mixing with seawater, which is likely due to the effect of cooling on metal sulfide precipitation and homogeneous equilibria. In contrast, pH of low temperature diffuse flow vent fluids at Galapagos decreases with increasing temperature achieving values approximately 0.5 units lower than ambient seawater at the discharge point, where the fluids are 22$\deg$C and directly associated with colonies of Riftia pachyptila. The ability to measure and monitor in-situ pH in real time offers great promise for future study as efforts continue to better understand the complex interplay between inorganic and organic processes associated with hydrothermal activity at mid-ocean ridges.
DE: 1020 Composition of the crust
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 3035 Midocean ridge processes
DE: 4815 Ecosystems, structure and dynamics
DE: 7218 Lithosphere and upper mantle
SC: Biogeosciences [B]
MN: 2003 Fall Meeting