HR: 1330h
AN: B12A-0771    [PDF]
TI: Vent Plume Characteristics at the Lost City Hydrothermal Field
AU: * Glickson, D A
EM: glickson@u.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Nakamura, K
EM: koichi.nakamura@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology (AIST), Institute for Marine Resources and Environment, Seafloor Environment and Resources Research Group 1, Tsukuba, Ibaraki, 305-8567 Japan
AU: Olson, E J
EM: olson@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Larson, B
EM: blarson@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Proskurowski, G
EM: giora@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Lilley, M D
EM: lilley@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Kelley, D S
EM: kelley@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AB: Lost City is a peridotite-hosted hydrothermal field driven by exothermic serpentinization reactions at depth. Venting of high pH (9-11), $40-90\deg$ C fluids and seawater promotes growth of carbonate structures that reach up to 60 m in height. To characterize the plume around this novel actively venting field and to investigate other potential venting sites, 14 CTD casts were completed in the vicinity of the field. In addition to potential temperature, conductivity, and oxygen, hydrocasts were also equipped with an Eh sensor to measure redox potential through the water column. Fluids from 11 of these casts were also sampled for hydrogen and methane, as these gases are byproducts of serpentinization reactions. To quantify the strongest hydrothermal signals, four casts were taken directly above and adjacent to Poseidon, the largest structure in the field (60 m tall, reaching to an elevation of 730 m). To place constraints on the extent of plume movement at Lost City, one cast was taken 125 m to the west, another 75 m to the east, and 2 were taken in a shallow depression that bounds the field 50-60 m to the north. Of the 9 casts proximal to the field, almost all showed a moderate to steep increase in Eh values 10-20 m off the bottom. Dramatic gradients in Eh occurred near bottom at all boundary stations as well. Hydrogen concentrations 100 times those of background ocean waters were measured near bottom at stations just north of the field and strong signals up to 20x background were measured near and to the east of Poseidon. Highly elevated methane concentrations were measured at the eastern boundary cast (180 nM), while other stations to the north and east of the main Lost City field had moderately elevated values (40-55 nM, up to 30x background). Higher concentrations of both hydrogen and methane were consistently found in the 750-800 m depth range. These data show that plumes derived solely from serpentinization reactions are characterized by steep gradients in Eh and elevated volatile concentrations very near bottom. In contrast to plumes associated with black smoker systems, the limited buoyancy of Lost City-like plumes and lack of particulate or strong thermal anomalies will make prospecting for other peridotite-hosted systems challenging.
DE: 3035 Midocean ridge processes
DE: 4820 Gases
SC: Biogeosciences [B]
MN: 2003 Fall Meeting