Nitrate supply and demand at the Georges Bank tidal front
E.P.W. Horne, J.W. Loder, W.G. Harrison, R. Mohn, M.R. Lewis, B. Irwin and T. Platt

New production, which uses NO3 as a nitrogen source, controls the net community production (or harvest) of an ecosystem. For Georges Bank the depth-integrated nitrate flux across its summertime tidal front is estimated from observations taken in July-August 1985 to be 12 mg at m-1s-1. Nutrient demand for the frontal (inside the nitrate-flux measurement site) and well-mixed areas of Georges Bank is found using the 15N technique to be 2.9 mg at N m-1s-1 and 2.5 mg at N m-1s-1, respectively. The measured flux is well in excess of that required to support the scallop population that exists near the frontal area. Additional measurements are required to determine the representativeness of the nutrient transfer and demand estimates, and to confirm the nutrient transfer mechanism(s). A leading candidate for the latter on the northern side of the Bank is the cross-frontal (Lagrangian) residual circulation associated with nonlinear tidal current interactions. Part of the scalar transport by this circulation appears in Eulerian measurements as a†ske7 eddy flux in the semidiurnal tidal band.

Keywords: nitrate flux, tidal front, new production, Georges Bank, skew flux, f-ratio
Contents of this volume Sci. Mar. 53(2-3) : 145-158 Back PDF
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