Cold Water Coral Mounds from the Porcupine Area: From Off-Mound Characterization Based from Planktonic and Benthic Foraminifera and Phosphorus Content in the Sediments

Stephan H. Margreth¹, Silvia Spezzaferri¹, Federica Tamburini², Andres Rüggeberg³, and Henk de Haas^4
1Department of Geosciences, University of Fribourg, Fribourg, Switzerland
²Pflanzenwissenschaften, ETH Zuerich, Lindau, Switzerland
³IFM-Geomar, Kiel, Germany
⁴Department of marine Chemistry and Geology, Royal Netherlands Institute for Sea Research, AB Den Burg (Texel), Netherlands

Cold water mounds dominated by the coral Lophelia pertusa occur along the European Atlantic margin from northern Norway to the Gulf of Cadiz. In October 2007, the Royal Netherland Institute for Sea Research organized the ESF CARBONATE Pelagia cruise M07II, to perform a pre-drilling, seismic and video survey on the Rockall Through margin. A multiproxy study was performed on surface samples from the box cores taken from on-off mounds in the region (quantitative analyses of foraminifera, phosphorus and mineralogical composition). The Rockall Bank, dominated by living Lophelia pertusa, displays high abundance of the benthic foraminifera Discoanomalina coronata and Globocassidulina subglobosa. High abundances of upwelling an/or high nutrient-preferring planktonic species (Globigerina bulloides and Globigerinita glutinata) occur at the surface. Foraminiferal data and the highest value of organic phosphorus from the area (2.667 µmol/g) suggest that probably only refractory organic matter reaches the sea floor on the Rockall Bank and its labile part is consumed by the vital activity of the cold water ecosystem. On-mound sediments from the Porcupine region contain very rare D. coronata and G. subglobosa, abundant Angulogerina angulosa and common Uvigerina spp.. Off-mound sediments display dominant Uvigerina spp., Hyalinea balthica, Bulimina and Cassidulina spp.. Organic phosphorus, respectively on-mound 2.063 µmol/g on the Porcupine Seabight and 2.184 µmol/g Magellan mound and off mound 2.393 µmol/g on the Porcupine Seabight, and 2.351 µmol/g on the Magellan mound, is lower than on the Rockall Bank. This suggests that probably a lower amount of organic matter is delivered to the sea floor in the Porcupine region, as also indicated by less abundant of upwelling or nutrient-loving species at the surface. This research is funded by Swiss National Found Grant N. 200021-117 928.

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