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Project Progress

Loihi Seamount is a submarine, active volcano located on the SE flanks of the Big Island of Hawaii, and it is considered to be the youngest volcano in the Hawaiian chain. Sites of vigorous and diffuse hydrothermal venting can be found on the seamount which are chemically distinct from other marine hydrothermal systems. The Loihi summit is located within a zone of low oxygen, enabling elevated iron(II) concentrations and support for a dominant community of iron-oxidizing bacteria. Our primary goal was to use an in situ voltammetric technique to map and investigate chemical redox dynamics within hydrothermally active fluids from Loihi Seamount. A secondary, more specific goal was to produce an in situ fine-scale (millimeter) vertical profile through a microbial mat using a deployable micromanipulator tripod. Additionally, we aimed to investigate Fe(II) oxidation kinetics for samples and cultures maintained by the Emerson group.

In situ electrochemical analyses: At the heart of the in situ voltammetric measurements is the In Situ Electrochemical Analyzer ISEATM (AIS, Inc.). A titanium pressure case (30cm long by 20cm diameter, rated to >10,000 psi) houses the analyzer consisting of a potentiostat, a 4-electrode multiplexer, and an internal computer. The pressure case was mounted in the Jason science basket. Real-time communication with the ISEA from the Jason control van was made possible via fiber optic tether and RS-232 cabling. Waterproof bulkhead connectors (Subconn, Inc.) allowed cabled connection to Jason’s 12VDC power source and RS-232 communication, 4 voltammetric working electrodes and one counter and reference electrode. We constructed a sensor wand consisting of up to four voltammetric working electrodes and the Jason temperature probe. We also mated a submersible micromanipulator (AIS, Inc.) to a custom tripod for making in situ profiles (MANIP, Micro Adjustable Non Instrusive Profiler). Parameters for individual voltammetric scans were set, and scans were visualized in real time. Individual scan analysis was conducted using a combination of the manufacturer’s software, a custom auto-analysis package, and Matlab.

On-deck electrochemical analyses: Hydrothermal fluids were also sampled using titanium major samplers. On-deck temperature, pH, and electrochemical measurements of discrete sub-samples were made using a standard DLK100a electrochemical analyzer (Analytical Instrument Systems, Inc.) and Thermo Electron pH meter. Microbial cultures for iron oxidizing bacteria were established and maintained by the Emerson group, and time-point measurements were made for pH and voltammetry in an effort to track and quantify iron oxidation rates. The in situ electrochemical analyses provided an efficient means for directed discrete sampling of hydrothermal fluids, and obtained high spatial resolution geochemical profiles through the microbial mats. This is part of an ongoing study to look at the biogeochemical roles played by the microbial communities in mediating water-rock alteration reactions on basalts.

Pending presentations and publications:

Edwards, KJ, Chan, C, Emerson, D, Glazer, BT, Huber, J, Kurz, M, Moyer, C, Rouxel, O, Staudigel, H, Tebo, B. (in prep) A novel low-temperature hydrothermal system at the base of a hot-spot volcanic seamount, Loihi, Hawaii.

Glazer, BT, Briggs, RA, Nuzzio, DB, Heshiki, Z, Edwards, KJ, Moyer, CL, Emerson, D, Tebo, BM, Staudigal, H. (in prep) Fine-scale profiling of hydrothermal fluid redox chemistry at the Loihi Seamount Microbial Observatory.

Glazer, BT, Edwards, KJ, Moyer, CL, Emerson, D, Tebo, BM, Staudigal, H. (in prep) Spatial extent and variability of redox chemistry in a massive seafloor iron-oxidizing microbial community at 5000m, Loihi, Hawaii.

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