Scale-up of sediment microbial fuel cells (SMFCs) is important to generating practical levels of power for undersea devices. Sustained operation of many sensors and communications systems require power in the range of 0.6 mW to 20 W. Small scale SMFC systems evaluated primarily in the laboratory indicate power densities for typical graphite plate anodes on the order of 10-50 mW m 22 . However, previous work also suggests that SMFC power production may not scale directly with size. Here, we describe a combination of lab and field studies to evaluate scale up for carbon fabric anodes with a projected surface area ranging from 25 cm 2 to 12 m 2 . The results indicate that power generation scales almost linearly with anode size up to about 1-2 m 2 of projected surface area. Our model suggests that anodes larger than this can experience significant reduction in power density, confirming laboratory observations. These results suggest that the majority of losses along the anode surface occur closest to the electronics, where the amount of current passing along an anode is the greatest. A multi-anode approach is discussed for SMFCs, suggesting that scale-up can be achieved using segmented anode arrays.

In 1983, current data were collected by the National Oceanic and Atmospheric Administration using mechanical current meters. During 1992 through 1996, acoustic Doppler current profilers as well as mechanical current meters and tide gauges were used. These measurements not only document tides and tidal currents in San Diego Bay, but also provide independent data sets for model calibration and verification. A high resolution (100‐m grid), depth‐averaged, numerical hydrodynamic model has been implemented for San Diego Bay to describe essential tidal hydrodynamic processes in the bay. The model is calibrated using the 1983 data set and verified using the more recent 1992–1996 data. Discrepancies between model predictions and field data in both model calibration and verification are on the order of the magnitude of uncertainties in the field data. The calibrated and verified numerical model has been used to quantify residence time and dilution and flushing of contaminant effluent into San Diego Bay. Furthermore, the numerical model has become an important research tool in ongoing hydrodynamic and water quality studies and in guiding future field data collection programs.

Hydrographic data (salinity, temperature, O9•, PO4, NOs and SiO9•) collected in the northern Gulf of California between February 27 and March 3, 1988, reveal that bottom water formation took place that winter. North of 30.5øN, salinity increased with depth from •35.30 practical salinity units (psu) at the surface to 35.57 psu at the bottom of the 200-m deep Wagner Basin; below-•25 m, temperature was almost homogeneous, at •15øC (•:0.4øC), with some inversions. The TS diagrams and the distribution of dissolved oxygen and nutrients suggest that the most likely origin of this bottom water is the shallow coastal region (•40 ra deep) of the northern Gulf. Elsewhere, the characteristic Gulf of California decrease of salinity with depth was found, from over 35.25 in the surface to 34.90 at 200 ra. In the upper •120 ra, intermediate salinity (35.0 to 35.3) and nutrient concentrations (phosphate, 1.5-2.0 pM; nitrate, 12-16 pM; and silicate, 25-32 pM) identify the Gulf of California Water this winter. In the deeper layers, low salinity (•35.0) and high nutrients (phosphate, •2.2 pM; nitrate, •22 pM; and silicate, •35 pM) indicate the presence of oceanic water from Guaymas Basin, probably Subsurface Subtropical Water. The boundary between the two regimes was •18 km wide, with clearly defmed bottom fronts and intrusions at all depths. Of the several late-winter hydrographic data sets available, only that from March 1973 presents a similar distribution of high-salinity bottom water. Therefore interannual variability (not necessarily E1 Nifio-Southern Oscillation (ENSO) related) can have a profound effect on vertical convection, which can occur both in ENSO and non-ENSO years. An important and as yet unexplained difference between the two data sets is that there was more Gulf of California Water in the northern Gulf of California in 1973 than in 1988. Introduction One of the most striking characteristics of the Gulf of California (GC, Figure 1) is its extremely high productivity [Gilbert and Allen, 1943; Alvarez-Borrego and Lara-Lara, 1991], in contrast to other enclosed seas such as the Mediterranean and the Red Sea. This is because the euphotic zone is constantly being supplied with nutrients by the thermohaline circulation, by tidal mixing, and by coastal upwelling [Alvarez-Borrego and Lara-Lara, 1991]. The distribution of nutrients in the Gulf of California is characterized by a monotonic increase with depth, the surface waters being almost depleted by biological activity, except in the area around the large Copyright 1995 by the American Geophysical Union. Paper number 95JC00138. 0148-0227/95/95JC-00138505.00 islands, presumably due to vertical mixing induced by the strong tidal currents [Alvarez-Borrego et al., 1978]. There is some evidence that the thermohaline circulation is the reverse of that in the Mediterranean [Bray, 1988a, Badan-Dangon et al., 1991], with an input at depth of cold, less salty, nutrient-rich oceanic water. This is possible because, despite strong evaporation (-•1 m/yr), the Gulf of California gain...

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