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[1] The biogeochemistry of continental shelf systems plays an important role in the global elemental cycling of nitrogen and carbon, but remains poorly quantified. We have developed a high-resolution physical-biological model for the U.S. east coast continental shelf and adjacent deep ocean that is nested within a basin-wide North Atlantic circulation model in order to estimate nitrogen fluxes in the shelf area of the Middle Atlantic Bight (MAB). Our biological model is a relatively simple representation of nitrogen cycling processes in the water column and organic matter remineralization at the water-sediment interface that explicitly accounts for sediment denitrification. Climatological and regionally integrated means of nitrate, ammonium, and surface chlorophyll are compared with its model equivalents and were found to agree within 1 standard deviation. We also present regional means of primary production and denitrification, and statistical measures of chlorophyll pattern variability. A nitrogen budget for the MAB shows that the sediment denitrification flux is quantitatively important in determining the availability of fixed nitrogen and shelf primary production (it was found to remove 90% of all the nitrogen entering the MAB). Extrapolation of nitrogen fluxes estimated for the MAB to the North Atlantic basin suggests that shelf denitrification removes 2.3 Â 10 12 mol N annually; this estimate exceeds estimates of N 2 fixation by up to an order of magnitude. Our results emphasize the importance of representing shelf processes in biogeochemical models.

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Using a one-layer quasi-geostrophic model, we study the effect of random monoscale topography on forced beta-plane turbulence. The forcing is a uniform steady wind stress that produces both a uniform large-scale zonal flow U (t) and smaller-scale macroturbulence characterized by both standing and transient eddies. The large-scale flow U is retarded by a combination of Ekman drag and the domain-averaged topographic form stress produced by the eddies. The topographic form stress typically balances most of the applied wind stress, while the Ekman drag provides all of the energy dissipation required to balance the wind work. A collection of statistically equilibrated numerical solutions delineates the main flow regimes and the dependence of the time-average of U on parameters such as the planetary vorticity gradient β and the statistical properties of the topography. We obtain asymptotic scaling laws for the strength of the large-scale flow U in the limiting cases of weak and strong forcing. If β is significantly smaller than the topographic PV gradient then the flow consists of stagnant pools attached to pockets of closed geostrophic contours. The stagnant dead zones are bordered by jets and the flow through the domain is concentrated into a narrow channel of open geostrophic contours. In most of the domain the flow is weak and thus the large-scale flow U is an unoccupied mean. If β is comparable to, or larger than, the topographic PV gradient then all geostrophic contours are open and the flow is uniformly distributed throughout the domain. In this open-contour case there is an "eddy saturation" regime in which U is insensitive to large changes in the wind stress. We show that eddy saturation requires strong transient eddies that act effectively as PV diffusion. This PV diffusion does not alter the kinetic energy of the standing eddies, but it does increase the topographic form stress by enhancing the correlation between topographic slope and the standing-eddy pressure field. Using bounds based on the energy and enstrophy power integrals we show that as the strength of the wind stress increases the flow transitions from a regime in which most of the form stress balances the wind stress to a regime in which the form stress is very small and large transport ensues.