Nepheloid layer distribution in the Benguela upwelling area offshore Namibia |
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| Institution: | 1. Oceans & Coasts Research Branch, Department of Environmental Affairs, Private Bag X4390, Cape Town 8000, South Africa;2. Marine Research Institute and Department of Oceanography, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;3. Farallon Institute, 101 H St. Suite Q, Petaluma, CA 94952, USA;4. Environmental Research Division, Southwest Fisheries Science Center, NOAA, Monterey, California, USA;5. Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Baey, 8012, South Africa;6. Marine Research Institute and Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;7. Bodega Marine Laboratory, University of California, Davis, P.O. Box 247, Bodega Bay, CA 94923, USA;1. Institut für Ostseeforschung Warnemünde (IOW), Seestraße 15, Rostock 18119, Germany;2. National Marine Information and Research Centre (NatMIRC), P.O. Box 912, Swakopmund, Namibia |
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| Abstract: | The distribution of nepheloid layers across the outer shelf and upper continental slope off Namibia was studied during a cruise with R.V. Meteor in late austral summer 2003. Optical measurements, carried out with a transmissometer and a backscattering fluorometer, are correlated with suspended particulate matter (SPM) and particulate organic carbon (POC) values from water sample filtration. Conductivity-temperature-depth and oxygen data are used to relate the nepheloid layers to hydrographic structures. The particle content of surface water at the continental slope is controlled primarily by the offshore extension of highly productive upwelling filaments. A pronounced bottom nepheloid layer (BNL) covers the entire area of study with maximum intensity above the outer shelf and at the shelf break—an area where erosional forces dominate. The detachment of this BNL at the shelf break feeds a major intermediate nepheloid layer (INL) at 25.5°S. This INL is positioned at 250–400 m depth, at the lower boundary of an oxygen minimum zone, and is likely connected to the poleward flow of South Atlantic Central Water (SACW) across the shelf break. Together, these strong subsurface nepheloid layers are indicators of intensive lateral particle transport from the outer shelf towards a depocenter of organic matter on the upper continental slope. |
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