HR: 1340h
AN: B13A-0170    [Abstracts]
TI: Time-series Deployment of Chemical Sensor Data-logger in a Riftia Patch at Tica Vent (EPR 9\deg50'N)
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
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AU: Zhang, Z
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AU: Yang, C
AF: Center of Ocean Science and Technology, Zhejiang University, 38 Zhada Lu, Hangzhou, ZJ 310027 China
AU: Foustoukos, D
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Mpls, MN 55455 United States
AB: An in-situ chemical sensor array was deployed in a Riftia pachyptila patch at Tica diffuse flow vent area during a recent submersible investigation with Atlantis/Alvin (At-11-7) to the EPR 9\deg50'N region. Chemical and temperature data were recorded continuously during the 13-day study to quantify short-term time series trends. Biological activity at Tica is unusually robust, which likely relates to a combination of chemical and physical factors in the vent ecosystem. The electrochemical array in the sensor unit consisted of pH, dissolved H$_{2}$ and H$_{2}$S electrodes, which made use of Ir, Pt and Ag base metal components respectively. The sensor measurements were referenced to dissolved Cl in the fluid using a junctioned Ag/AgCl electrode. A Ti sheathed E-type thermocouple was included to provide simultaneous temperature data. Moreover, the sensor array was coupled to a data-logging system through a high pressure conducting cable, which allowed continuous data scanning and recording at an interval of 5 seconds. Owing to the functionality of the inductively coupled communication link (ICL) between the sensor and the data logger, we were able to use real time temperature readings in the submersible to guide deployment. The warmest temperatures were observed at the fractured rock base of the tubeworm colony, which is where the sensor package was deployed. Temperature, however, varied systematically from approximately 10 to 20\deg C throughout the 13-day experiment. Chemical data were generally in phase with temperature with the more extreme departures from ambient conditions associated with temperature maxima. In general, the lowest pH values were approximately 0.5 units less than ambient seawater, while dissolved H$_{2}$S concentrations ranged from 10 and 100 $\mu$ mol/kg. The mean value of dissolved H$_{2}$S was in the range of 20-30 $\mu$ mol/kg in excellent agreement with that actually measured using conventional approaches. Dissolved H$_{2}$ concentrations, in contrast, were orders of magnitude lower and ranged from 10$^{-9}$ to 3x10$^{-8}$ $\mu$ mol/kg. To out knowledge these are the first in-situ time series dissolved H$_{2}$ data and are clearly relevant to the geomicrobiological processes affecting dispersed flow hydrothermal systems at mid-ocean ridges. During the course of our study, other chemical and temperature sensors were deployed and re-deployed at different vent sites by Alvin for variable times and at different (P-T-X) conditions. The chemical sensors proved to be highly mobile, robust and performed very well during all seafloor trials.
DE: 4832 Hydrothermal systems
DE: 4894 Instruments and techniques
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1094 Instruments and techniques
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting