Carbon and nitrogen fluxes across the Hebridean shelf break, estimated by a 2D coupled physical–microbiological model

A two-dimensional coupled physical–biological model is described and used to compute the annual cycle of primary production across the Hebridean shelf and slope based on information collected during the Land Ocean Interaction Study (LOIS), with the focus on data for 1995. Calculations of modelled carbon and nitrate fluxes indicate an annual on-shelf near-surface flux of nitrate of 65 kmol N m−1 year−1 at the top of the slope (140 m deep) and an off-shelf near-bottom carbon flux of 23 kmol C m−1 year−1. Further down the slope (at 300 m deep) the on-shelf nitrate flux increased to 126 kmol N m−1 year−1 and the off-shelf carbon flux increased to 41 kmol C m−1 year−1. Carbon deposition to the sea floor was less than 0.4 mol C m−2 year−1 on the upper slope and 1.1 mol C m−2 year−1 lower down the slope, values which are four-fold lower than those inferred from benthic oxygen demand measurements made during the Shelf Edge Study but of similar magnitude to observations made during OMEX I.