Hydrothermal Activity in Bransfield Strait, Antarctica: Sample Analysis and Data Reduction

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OPP 9615259 Klinkhammer In the austral summer of 1995 a research team from Oregon State University conducted a survey of hydrothermal activity in the Bransfield Strait (cruise NBP9507). The approach was to search the water column for the types of anomalies in temperature, turbidity, and chemistry that are known to be indicative of hydrothermal plumes in mid-ocean ridge settings. This work produced a detailed picture of the hydrography of this area in addition to locating three active hydrothermal areas in the Central Basin. These are the first deep ocean hydrothermal sites ever discovered in a polar region. A plume being discharged to the Strait through the entrance to the sunken caldera at Deception Island was also discovered. Follow-up research on these discoveries is important for several reasons: (1) Bransfield is isolated from the system of mid-ocean ridges and has a relatively short history of rifting (approximately 4 my). So, while the Bransfield straddles the Atlantic and Pacific, vent biota in the Strait may well have a distinct genealogy. It will not be possible to sample biota until the water analyses and data interpretation are completed. (2) Bransfield is a backarc rift system. It is likely that the vent fluids and mineral deposits associated with venting in this setting are unlike anything sampled so far. The closest analogy is probably the Okinawa Trough or Lau Basin where native gold is part of the hydrothermal assemblage. (3) Bransfield is in a sensitive position as far as world climate and regional productivity. Preliminary evidence suggests that Deception Island is a significant source of hydrothermally affected water to the surface waters of the Strait. Consequently, it as important to quantify this flux and access the biogeochemical impact of this phenomenon. (4) Bransfield is a rift zone which has little spreading or, if spreading is occurring, it began in the recent past. On the other hand there is a definite tectonic fa bric that separates the Strait into three distinct basins. This situation allows an opportunity to study the impact of tectonic processes on the emplacement of hydrothermal circulation cells. The success of the NBP9507 cruise has led to an enormous amount of information on the water column in the Bransfield, both in terms of the amount of data collected by instrument packages and in the number of water samples that were taken for analysis. Over 100 water samples from the Bransfield are available for analysis for total dissolvable manganese. This award supports research to complete this analytical program and to analyze the results. These data will provide information about the nature of hydrothermal activity in the Strait which will be invaluable in understanding the role of hydrothermal waters in regional oceanography and for planning future work.