HR: 17:30h
AN: V44A-07 INVITED     [Abstracts]
TI: Characteristics of Hydrothermal Activity in the Lau Back Arc Basin
AU: * Resing, J
EM: resing@u.washington.edu
AF: University of Washington, JISAO-NOAA-PMEL 7600 Sand Point Way, Seatle, WA 98115 United States
AU: Baker, E
AF: Pacific Marine Environmental Lab, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Martinez, F
AF: University of Hawaii, POST Building, Honolulu, HA 96822 United States
AU: Lebon, G
AF: University of Washington, JISAO-NOAA-PMEL 7600 Sand Point Way, Seatle, WA 98115 United States
AU: Walker, S
AF: Pacific Marine Environmental Lab, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Massoth, G
AF: Institute of Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, 1 New Zealand
AU: Taylor, B
AF: University of Hawaii, POST Building, Honolulu, HA 96822 United States
AU: Lupton, J
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center, Newport, OR 97365 United States
AU: Greene, R
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center, Newport, OR 97365 United States
AU: Nakamura, K
AF: National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba Ibaraki, 305-8567 Japan
AU: Smith, J
AF: University of Hawaii, POST Building, Honolulu, HA 96822 United States
AB: In April and May 2004, we conducted extensive surveys of hydrothermal plumes along the East Lau Spreading Center (ELSC), including the Valu Fa Ridge, in an initial effort to deliniate the extent and nature of hydrothermal venting along these ridges. This was the first step in identifying a focus site for the Ridge 2000 Lau Back Arc Basin ISS. We sampled these plumes from the RV Kila Moana using CTD tows and casts and by mounting a variety of plume-sensitive sensors on the DSL-20 side scan sonar system. Our survey documented extensive venting with complex chemical signatures at more than 20 locations along 400 km of ridge axis. Here, we examine the chemistry of the plumes based on samples that were collected for Helium isotopes, total carbon dioxide, pH, particulate chemistry, and total and dissolved Fe and Mn. There were several predominant chemical characteristics of the plumes: 1. The particulate matter that produced the optical backscatter plumes in the VFR region (22.7-21.4S) was dominated by Fe-oxyhydroxides and metal sulfides while the majority of the plumes on the ELSC (21.4-19.3S) were dominated by elemental sulfur and, to a lesser extent, by Fe-oxyhydroxides. 2. The ratio of Fe to S at Valu Fa was $\sim$2:1, but was a factor of 10 lower ($\sim$0.2:1) in the plumes further north. 3. In the areas where particulate sulfur was rich, there was a wide range of dissolved Mn concentrations. 4. Elevated levels of particulate Mn are concentrated at 21øS suggesting a buildup of hydrothermal effluent in the basin. The differences between plumes over Valu Fa and the rest of the ELSC have significant implications for the establishment of the Lau ISS. The high Fe:S ratio at Valu Fa suggests that organisms that require hydrogen sulfide for their metabolism might be scarce in this area, while areas farther north may better support vent organisms. The abundance of particulate elemental S in the north further suggests (based on MOR models)that the vents forming the plumes are located in areas of recent volcanism (0-5+ years). These are areas where evolutionary characteristics of back arc hydrothermal systems might be studied. However, the proximity of the Valu Fa Ridge to a volcanic arc and the silicic lavas erupted there distinguish it from well studied MOR spreading centers. These results indicate that the RIDGE community will need to consider along-ridge differences in vent chemistry ecological richness, and geology in the decision on where to establish the focus site of the Lau ISS.
DE: 4832 Hydrothermal systems
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting