Solid-state microelectrodes have been used in situ in Raritan Bay, NJ to measure pore water profiles of dissolved O 2, Mn, Fe, and sulfide at (sub)millimeter resolution by voltammetric techniques. The voltammetric sensor was positioned with microprofiling instrumentation mounted on a small remote operated vehicle (ROV). This instrumentation and the sensor were controlled and monitored in real time from a research vessel anchored at the study site. The voltammetric analyzer was connected to the electrodes of the voltammetric cell with a 30 m cable which also bridged receiver-transmitter transducers to ensure signal quality along the cable. Single analyte O 2, pH, and resistivity microsensors were operated alongside the voltammetric sensor. We report on the technology of the system and the concentration changes of redox species observed from 2 to 3 cm above to approximately 4 cm below the sediment−water interface during three deployments. O 2 measurements from both Clark and voltammetric electrodes were in excellent agreement. The profiles obtained show that there is no detectable overlap of O 2 and Mn 2+ in the sediments which is similar to previous reports from other continental margin sediments which were cored and analyzed in the laboratory. These data indicate that O 2 is not a direct oxidant for Mn 2+ when diffusive (rather than advective) processes control the transport of solutes within the sediment. Subsurface Mn 2+ peaks were observed at about 2 cm and coincide with a subsurface pH maximum. The data can be explained by organic matter decomposition with alternate electron acceptors and by the formation of authigenic phases containing reduced Mn at depth.
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Luther et al. (1999) studied this question.
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