Integrated Ocean Drilling Program (IODP) Expedition 301, on the eastern flank of the Juan de Fuca Ridge, established part of a three-dimensional network of borehole observatories (Circulation Obviation Retrofit Kits [CORKs]) in the oceanic crust. These observatories are to be used to conduct active, multidisciplinary experiments over timescales of minutes to years and length scales of meters to kilometers. The complete experimental program will comprise two IODP expeditions (the first having been Expedition 301, the second to be scheduled), an offset seismic experiment, and long-term monitoring and crosshole testing carried out by submersible and remotely operated vehicle. During Expedition 301, we replaced a preexisting CORK observatory in Hole 1026B and created and instrumented new Holes U1301A and U1301B, which penetrate 108 and 320 m into basement, respectively. The borehole observatories deployed during Expedition 301 share some characteristics with systems deployed during the Ocean Drilling Program but also include many improved components and novel features.

[1] The Integrated Ocean Drilling Program (IODP) Hole 1301A on the eastern flank of Juan de Fuca Ridge was used in the first long-term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole. Three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks. Following recovery of the colonization systems, we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples. We also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine R2A medium and identified isolates by partial 16S or 18S rDNA sequencing. We found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron. Fe(II)-rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles, as well as the only culturable organotrophic thermophiles. These results suggest that olivine (a common igneous mineral) in seawater-recharged ocean crust is capable of supporting microbial communities, that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes, and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust.

Integrated Ocean Drilling Program Expedition 301 was preceded during 2000 and 2002 by three surveys that helped to delineate seafloor and basement relief, sediment thickness, and the nature of ridge-flank hydrothermal conditions and processes on the eastern flank of the Juan de Fuca Ridge. These surveys generated swath map, seismic, and thermal data used to select locations for primary and secondary drilling targets, building from several decades of earlier work. We show compilations and examples of data from several characteristic settings in and around the Expedition 301 work area and use these observations to evaluate sedimentation patterns and thermal conditions in basement. There remain important unanswered questions in this area concerning fluid circulation within the upper oceanic crust, the magnitude of lithospheric heat input, the quantitative significance of advective heat loss from the crust, and relations between basement relief, sedimentation, and sediment alteration. These questions may be resolved through collection of a modest amount of additional data focusing on a few critical locations.

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We describe a new chamber-based benthic microbial fuel cell (BMFC) that incorporates a suspended, high surface area and semi-enclosed anode to improve performance. In Yaquina Bay, OR, two chambered BMFC prototypes generated current continuously for over 200 days. One BMFC was pumped intermittently, which produced power densities more than an order of magnitude greater than those achieved by previous BMFCs with single buried graphite-plate anodes. On average, the continuous power densities with pumping were 233 mW/m2 (2.3 W/m3); peak values were 380 mW/m2 (3.8 W/m3), and performance improved over the time of the deployments. Without pumping, high power densities could similarly be achieved after either BMFC was allowed to rest at open circuit. A third chambered BMFC with a 0.4 m2 footprint was deployed at a cold seep in Monterey Canyon, CA to test the new design in an environment with natural advection. The power density increased 5-fold (140 mW/m2 vs 28 mW/m2) when low-pressure check valves allowed unidirectional flow through the chamber.

Supported by the natural potential difference between anoxic sediment and oxic seawater, benthic microbial fuel cells (BMFCs) promise to be ideal power sources for certain low-power marine sensors and communication devices. In this study a chambered BMFC with a 0.25 m(2) footprint was used to power an acoustic modem interfaced with an oceanographic sensor that measures dissolved oxygen and temperature. The experiment was conducted in Yaquina Bay, Oregon over 50 days. Several improvements were made in the BMFC design and power management system based on lessons learned from earlier prototypes. The energy was harvested by a dynamic gain charge pump circuit that maintains a desired point on the BMFC's power curve and stores the energy in a 200 F supercapacitor. The system also used an ultralow power microcontroller and quartz clock to read the oxygen/temperature sensor hourly, store data with a time stamp, and perform daily polarizations. Data records were transmitted to the surface by the acoustic modem every 1-5 days after receiving an acoustic prompt from a surface hydrophone. After jump-starting energy production with supplemental macroalgae placed in the BMFC's anode chamber, the average power density of the BMFC adjusted to 44 mW/m(2) of seafloor area which is better than past demonstrations at this site. The highest power density was 158 mW/m(2), and the useful energy produced and stored was ≥ 1.7 times the energy required to operate the system.

Improving microbial fuel cell (MFC) performance continues to be the subject of research, yet the role of operating conditions, specifically duty cycling, on MFC performance has been modestly addressed. We present a series of studies in which we use a 15-anode environmental MFC to explore how duty cycling (variations in the time an anode is connected) influences cumulative charge, current, and microbial composition. The data reveal particular switching intervals that result in the greatest time-normalized current. When disconnection times are sufficiently short, there is a striking decrease in current due to an increase in the overall electrode reaction resistance. This was observed over a number of whole cell potentials. Based on these results, we posit that replenishment of depleted electron donors within the biofilm and surrounding diffusion layer is necessary for maximum charge transfer, and that proton flux may be not limiting in the highly buffered aqueous phases that are common among environmental MFCs. Surprisingly, microbial diversity analyses found no discernible difference in gross community composition among duty cycling treatments, suggesting that duty cycling itself has little or no effect. Such duty cycling experiments are valuable in determining which factors govern performance of bioelectrochemical systems and might also be used to optimize field-deployed systems.

There is widespread interest in developing methods to investigate in situ microbial activity in subsurface environments. Novel experiments based on single borehole push–pull methods were conducted to measure in situ microbial activity at the Äspö Hard Rock Laboratory (HRL). Microbial nitrate reduction and lactate consumption were measured at in situ conditions at a depth of 450 m in the HRL tunnel. A circulation system was used to circulate ground water from the aquifer through pressure‐maintaining flow cells containing coupons for biofilm growth. The system allows microbial investigations at in situ pressure, temperature and chemistry. Four experiments were conducted in which a combination of a conservative tracer, nitrate and lactate was injected into the circulation system. Rate of nitrate utilization was 5 µm h−1 without lactate and 13 µm h−1 with lactate. Lactate consumption increased from 30  to 50 µm h−1 with the addition of an exogenous electron acceptor (nitrate). Attached and unattached cells were enumerated using epifluorescence microscopy to calculate cell‐specific rates of activity. The biofilm had an average cell density of 1 × 106 cells cm−2 and there was an average of 6 × 105 unattached cells mL−1 in circulation. Cell‐specific rates of lactate consumption were higher than previously reported using radiotracer methods in similar environments. The differences highlight the importance of conducting microbial investigations at in situ conditions. The results demonstrate that an indigenous community of microbes survives at a depth of 450 m in the Fennoscandian shield aquifer with the potential to oxidize simple organic molecules such as lactate.