In many marine environments, a voltage gradient exists across the water sediment interface resulting from sedimentary microbial activity. Here we show that a fuel cell consisting of an anode embedded in marine sediment and a cathode in overlying seawater can use this voltage gradient to generate electrical power in situ. Fuel cells of this design generated sustained power in a boat basin carved into a salt marsh near Tuckerton, New Jersey, and in the Yaquina Bay Estuary near Newport, Oregon. Retrieval and analysis of the Tuckerton fuel cell indicates that power generation results from at least two anode reactions: oxidation of sediment sulfide (a by-product of microbial oxidation of sedimentary organic carbon) and oxidation of sedimentary organic carbon catalyzed by microorganisms colonizing the anode. These results demonstrate in real marine environments a new form of power generation that uses an immense, renewable energy reservoir (sedimentary organic carbon) and has near-immediate application.

The microbial communities associated with electrodes from underwater fuel cells harvesting electricity from five different aquatic sediments were investigated. Three fuel cells were constructed with marine, salt-marsh, or freshwater sediments incubated in the laboratory. Fuel cells were also deployed in the field in salt marsh sediments in New Jersey and estuarine sediments in Oregon, USA. All of the sediments produced comparable amounts of power. Analysis of 16S rRNA gene sequences after 3-7 months of incubation demonstrated that all of the energy-harvesting anodes were highly enriched in microorganisms in the delta-Proteobacteria when compared with control electrodes not connected to a cathode. Geobacteraceae accounted for the majority of delta-Proteobacterial sequences or all of the energy-harvesting anodes, except the one deployed at the Oregon estuarine site. Quantitative PCR analysis of 16S rRNA genes and culturing studies indicated that Geobacteraceae were 100-fold more abundant on the marine-deployed anodes versus controls. Sequences most similar to microorganisms in the family Desulfobulbaceae predominated on the anode deployed in the estuarine sediments, and a significant proportion of the sequences recovered from the freshwater anodes were closely related to the Fe(III)-reducing isolate, Geothrix fermentans. There was also a specific enrichment of microorganisms on energy harvesting cathodes, but the enriched populations varied with the sediment/water source. Thus, future studies designed to help optimize the harvesting of electricity from aquatic sediments or waste organic matter should focus on the electrode interactions of these microorganisms which are most competitive in colonizing anodes and cathodes.

Pairs of platinum mesh or graphite fiber-based electrodes, one embedded in marine sediment (anode), the other in proximal seawater (cathode), have been used to harvest low-level power from natural, microbe established, voltage gradients at marine sediment-seawater interfaces in laboratory aquaria. The sustained power harvested thus far has been on the order of 0.01 W/m2 of electrode geometric area but is dependent on electrode design, sediment composition, and temperature. It is proposed that the sediment/anode-seawater/cathode configuration constitutes a microbial fuel cell in which power results from the net oxidation of sediment organic matter by dissolved seawater oxygen. Considering typical sediment organic carbon contents, typical fluxes of additional reduced carbon by sedimentation to sea floors < 1,000 m deep, and the proven viability of dissolved seawater oxygen as an oxidant for power generation by seawater batteries, it is calculated that optimized power supplies based on the phenomenon demonstrated here could power oceanographic instruments deployed for routine long-term monitoring operations in the coastal ocean.

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In situ microelectrode, box‐core pore water gradient, and in situ benthic chamber estimates of organic carbon degradation and CaCO3 dissolution are combined with organic‐C and carbonate‐C accumulation rates to approximate the total carbon flux to the seafloor along two transects of the continental slope and rise off central California. Microelectrode profiles of dissolved O2 demonstrate that sediments at 13 sites, ranging in water depth from 580 to 4080 m, become anoxic below the uppermost 0.4–3 cm of the sediment column. If a current‐swept area of nondeposition on the upper slope is excluded, we find total organic‐C and carbonate‐C fluxes to the seafloor vary from 40 to 100 μmol C cm−2yr−1 and from 32 to 91 μmol C cm−2yr−1, respectively. From the distribution of these fluxes there is no indication that total fluxes or remineralization rates of organic or carbonate carbon are influenced markedly by conditions in the oxygen minimum zone. Instead, the upper continental rise with its system of submarine valleys and fans stands out as the most important locus for carbon deposition and remineralization. When benthic fluxes and burial rates are extrapolated over the whole slope and rise of the region, aerobic respiration is the major mechanism of organic matter oxidation, and organic‐C and carbonate‐C recycling are on average 87% and 98% efficient, respectively. These results suggest that modern sediments on the outer regions of continental margins are important sources of CO2 that is injected directly into ocean deep water. However, if benthic carbon fluxes on the central California margin are typical of margins globally, this injection rate is less than 0.7 Gt C yr−1, which does not indicate a significant anthropogenic enhancement of carbon export to continental slopes and rises.