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www.ocean-sci-discuss.net/6/1061/2009/
doi:10.5194/osd-6-1061-2009
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Deep ocean exchange with west-European shelf seas
Proudman Oceanographic Laboratory, 6 Brownlow Street, Liverpool L3 5DA, UK
Abstract. We review mechanisms and studies of exchange between the north-east Atlantic and the adjacent shelf sea. Mechanisms include: well-developed summer upwelling and associated filaments off Portugal and north-west Spain giving exchange O(3 m2/s per unit length of shelf); prevailing westerly winds further north driving exchange O(1 m2/s); poleward flow along most of the upper slope with associated secondary circulation O(1 m2/s); meanders and eddies in this poleward flow; eddies shed from slope waters into the Bay of Biscay; local exchanges at shelf spurs and depressions or canyons (e.g. dense-water cascading of order 1 m2/s). Tidal transports are larger; their reversal every six hours makes exchange largely ineffective except where internal tides are large and non-linear, as in the Celtic Sea where solitons carry water with exchange O(1 m2/s). These various physical exchanges amount to an estimated 2–3 m2/s per unit length of shelf, between ocean and shelf; a numerical model estimate is comparable: 2.5×106 m3/s onto and off the shelf from Brittany to Norway. Mixing controls the seasonal thermocline, affecting primary production and hence fluxes and fate of organic matter. Specifically, CO2 take-up by primary production, settling below the thermocline before respiration, and then off-shelf transport, make an effective shelf-sea "pump" (for CO2 from the atmosphere to the deep ocean). However, knowledge of biogeochemical fluxes is generally sparse; there is scope for more measurements, model validation and estimates from models.
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Citation: Huthnance, J. M., Holt, J. T., and Wakelin, S. L.: Deep ocean exchange with west-European shelf seas, Ocean Sci. Discuss., 6, 1061-1092, doi:10.5194/osd-6-1061-2009, 2009. Bibtex EndNote Reference Manager XML
