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Turbidity of waters over the Northwest Iberian continental margin

McCave, I. N. and Hall, Ian Robert 2002. Turbidity of waters over the Northwest Iberian continental margin. Progress in Oceanography 52 (2-4) , pp. 299-313. 10.1016/S0079-6611(02)00012-5

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Abstract

In OMEX-II-II, 9 cruises gathered optical data, principally by transmissometer. The distribution of optical turbidity caused by concentration of particulate matter (PMC) in the water column over the northern Iberianmargin shows several features related to hydrography. It is concluded that a signal of PMC seen in Mediterranean Water (MW) found north of 42°N is not carried from its source at the Gibraltar Sill and Gulf of Cadiz because it is shown, using intermediate stations, that this turbid plume decays, mainly by fall out but also partly by mixing, to very low levels around southern Portugal. PMC maxima sometimes seen in MW on the northern Iberianmargin are thus most likely to result from intermittent local resuspension by MW interacting with slope sediments. The highest turbidity is found over the upper slope and is the result of (i) shelf edge resuspension and off-shelf flow of turbid plumes, mainly between 100 and 300 m depth, and (ii) resuspension under the slope current aided by internal waves, in the depth range 500–800 m where the density gradient between ENACW and MW is maximal. Below the MW, flows are generally slow, and turbidity is low. The bottom nepheloid layer in deep water is also weak with PMC values <100 mg m-3. The focus of resuspension activity on the upper slope means that the region is an efficient exporter to the ocean of sediment that either escapes from the shelf or sinks to the bed from surface production. This accounts for upper slope sediments recorded in other studies as sandy or in places as rocky bottom.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Publisher: Elsevier
ISSN: 0079-6611
Last Modified: 04 Jun 2017 04:00
URI: http://orca.cf.ac.uk/id/eprint/30553

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