Hydrography and silica budget of the Angola Basin
Van Bennekom, A.J.; Berger, G.W. (1984). Hydrography and silica budget of the Angola Basin. Neth. J. Sea Res. 17(2-4): 149-200
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, more
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| Authors | | Top |
- Van Bennekom, A.J., more
- Berger, G.W.
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| Abstract |
Water masses and circulation patterns in the Angola Basin are reviewed, with emphasis on the region of the Zaire river plume and the Zaire deep sea fan. The edge of the Zaire river plume is found at ~800km from the river mouth, in February and March in SW direction, in May and July in W direction and in November in NW direction. The thickness of the plume waters increases from less than 5 m near the river mouth to ~ 25 m near the edge of the plume. The oceanic waters below and besides the plume are formed by interaction of eastward moving shallow undercurrent waters and northward moving waters of (sub)arctic origin. Nitrate-salinity graphs are used to distinguish between these water masses, and Benguela current waters are detected up to 5°S in a narrow subsurface tongue off the continental shelf.The complicated current patterns lead to various fronts, gyres and domes which advect nutrients into the euphotic zone. Particularly south of the Zaire river plume, the primary production is relatively high and diatoms play a substantial part in it. Diatom production is also high in the Zaire river plume between salinities of 28 and 32, where 40 to 90% of the dissolved silica advected by the Zaire river is converted into diatoms. Sections through the Zaire canyon show enhanced vertical mixing, and from the salinity distribution net up-canyon movement of the bottom waters is suggested. The bottom waters at the base of the continental slope have slightly less oxygen and slightly more nutrients (especially PO4) than the bottom waters in the central part of the Angola Basin. About 80% of the increase in dissolved phosphate probably results from desorption of the phosphate absorbed on suspended material in the inner part of the canyon. |
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