Deep ocean exchange with west-European shelf seas
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 m**2/s per unit length of shelf); prevailing westerly winds furt...
| Main Authors: | , , |
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| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Copernicus Publications
2009
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| Subjects: | |
| Online Access: | http://nora.nerc.ac.uk/id/eprint/7419/ https://nora.nerc.ac.uk/id/eprint/7419/1/DOESjmhOsdNORA.pdf https://nora.nerc.ac.uk/id/eprint/7419/2/DOESjmhf01.pdf https://nora.nerc.ac.uk/id/eprint/7419/3/DOESjmhf02.pdf https://nora.nerc.ac.uk/id/eprint/7419/4/DOESjmhf03.pdf https://nora.nerc.ac.uk/id/eprint/7419/5/DOESjmhf04.pdf http://www.ocean-sci-discuss.net/6/1061/2009/osd-6-1061-2009.pdf |
| Summary: | 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 m**2/s per unit length of shelf); prevailing westerly winds further north driving exchange O(1 m**2/s); poleward flow along most of the upper slope with associated secondary circulation O(1 m**2/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 m**2/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 m**2/s). These various physical exchanges amount to an estimated 2-3 m**2/s per unit length of shelf, between ocean and shelf; a numerical model estimate is comparable: 2.5 x 106 m**3/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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