Deployable in Situ Electrochemical Analyzer (ISEA) for Remote and Automatic Analysis of O2, H2S and Sulfur Species in Hydrothermal Vent Environments

University Of Delaware, Newark DE

Investigators

Abstract

P.I. Luther 0136671 This project proposes to purchase an in situ electrochemical analyzer (ISEA) that can be deployed at any ocean depth on landers, moorings and CTD type profilers for remote aquatic experiments in waters and porewaters. With this instrument, many redox species can be determined simultaneously by voltammetry at a gold-amalgam solid-state electrode during one potential scan. These species include dissolved oxygen, sulfide, thiosulfate, polysulfides, iodide, Fe(II), Mn(II), and FeS. Oxygen can be measured with high precision and sensitivity as can total dissolved sulfide. No chemical manipulations are necessary for measurement and up to four working electrodes can be mounted at different depths and locations to obtain chemical information in the water column. This analyzer is ideal for monitoring important redox regimes such as the development of seasonal anoxia in nearshore and shelf environments, the changes in sulfur chemistry at hydrothermal vents and the profiles of redox species in sediments, stagnant bays, estuaries and basins. In a previous submission, these areas of study were targeted for making measurements but the reviewers indicated that this was too ambitious and only one should be selected for further work. In this proposal, the focus is on hydrothermal vent research. A major concern at vents is; what are the changes in vent and diffuse flow chemistry that affect the way organisms colonize different sites? Recent work has shown that different biological organisms reside in different chemical niches. Thus, in situ sensors that can measure a variety of redox species would be ideal for improving our understanding of biogeochemical studies of water chemistry on temporal and spatial scales in these environments. A prototype in situ electrochemical analyzer has been successfully used on the DSV Alvin and is now commercially available from Analytical Instrument Systems, Inc. This system was designed to use DC power from DSV Alvin with electrodes deployed at given vent locations by the submarine's manipulators controlled by an operator in the submersible. The next step in development of this technology is to add remote or automatic capability to the system to monitor temporal changes in a variety of systems. Although the ISEA is a single system, it will have four Au/Hg working electrodes with four temperature and pH sensors integrated with each of the working electrodes. In essence, the ISEA is four separate instrument packages for voltammetry, temperature and pH in one analyzer, which permits analysis of four separate locations/depths. As part of this proposal the gold-amalgam (Au/Hg) electrodes will be tested for long-term deployment. The testing will include long-term deployment in estuarine waters at the University of Delaware's harbor and at hydrothermal vent waters.