Regional primary productivity differences off Morocco (NW-Africa) recorded by modern benthic foraminifera and their stable carbon isotopic composition |
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| Institution: | 1. Departamento de Geología, Universidad de Salamanca, Salamanca, Spain;2. Div. de Geologia e Georecursos Marinhos, Instituto Português do Mar e da Atmosfera, Lisboa, Centro de Ciencias do Mar, Univ. Algarve, Faro, Portugal;3. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, UK;1. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK;2. Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;3. Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, Scotland, UK;4. International Ocean Discovery Program, Texas A&M University, College Station, TX, USA;1. National Institute of Oceanography, Dona Paula, Goa, India;2. Alfred Wegner Institute for Polar and Marine Research, Bremerhaven, Germany;3. Department of Earth Science and Marine Science Institute, University of California, Santa Barbara 93106-9630, USA;4. Banaras Hindu University, Varanasi, India;1. Micropaleontology Laboratory, Geological Oceanography Division, National Institute of Oceanography, Goa, India;2. Department of Earth Science, University of California, Santa Barbara 93106-9630, USA;3. Alfred Wegner Institute for Polar and Marine Research, Bremerhaven, Germany |
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| Abstract: | The influence of different primary productivity regimes on live (Rose Bengal stained) and dead benthic foraminiferal distribution, as well as on the stable carbon isotopic composition of foraminiferal tests, was investigated in sediment surface samples (0–1 cm) from the upwelling region off Morocco between Cape Ghir (31°N) and Cape Yubi (27°N). A combination of factor analysis, detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) was applied to the benthic foraminiferal data sets. Five major assemblages for both the live and dead fauna were revealed by factor analysis. In the cape regions organic matter fluxes are enhanced by high chlorophyll-α concentrations in the overlying surface waters. Here, benthic foraminiferal faunas are characterized by identical live and dead assemblages, high standing stocks, and low species δ13C values, indicating constant year-round high productivity. Bulimina marginata dominates the unique fauna at the shallowest station off Cape Ghir indicating highest chlorophyll-a concentrations. Off both capes, the succession of the Bulimina aculeata/Uvigerina mediterranea assemblage, the Sphaeroidina bulloides/Gavelinopsis translucens assemblage, and the Hoeglundina elegans assemblage from the shelf to the deep sea reflects the decrease in chlorophyll-a concentrations, hence the export flux. In contrast, the area between the capes is characterized by differently composed live and dead assemblages, low standing stocks, and less depleted δ13C values, thus reflecting low primary productivity. High foraminiferal numbers of Epistominella exigua, Eponides pusillus, and Globocassidulina subglobosa in the dead fauna indicate a seasonally varying primary productivity signal. Significantly lower mean δ13C values were recorded in Bulimina mexicana, Cibicidoides kullenbergi, H. elegans, U. mediterranea and Uvigerina peregrina. Cibicidoides wuellerstorfi is a faithful recorder of bottom water δ13C in the Canary Islands regions. The mean δ13C signal of this species is not significantly influenced by constant high organic matter fluxes. The species-specific offset between live and dead specimens is the same. |
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