|Lateral and temporal variability of bottom currents near the Pen Duick Escarpment|
Vangampelaere, E. (2010). Lateral and temporal variability of bottom currents near the Pen Duick Escarpment. RCMG/MareLac: Gent. 34 pp.
Gulf of Cadiz; paleoceanography; Pen Duick Escarpment; cold-water corals; water masses
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The Gulf of Cadiz is known for its complex hydrodynamic setting and the occurrence of cold- water corals (CWC). Most of the research is performed on the Iberian shelf due to the presence of the Mediterranean Outflow Water (MOW). Along the Northern European margin this water mass has an influence on the existence of the CWC as it is a water mass with high amounts of suspended material. Though CWC can also reside outside the MOW region, the Pen Duick Escarpment (PDE) off the coast of Larache is one of such regions. In this region the dominant water masses are the Antarctic Intermediate Water (AAIW) and the North Atlantic Central Water (NACW). The sediment particles are mainly in suspension due to interaction with the topographic relief and water masses, creating internal tides. Between the water masses an interface provides lateral sediment transport. However, these interactions and the paleoceanography of AAIW and NACW on the Moroccan shelf are poorly known. The objective of this study is to obtain a paleoceanographic understanding of water mass dynamics from the Last Glacial Maximum (LGM) till now in the El Arraiche mud volcano field, more specifically on the PDE. Based on grain-size, X-Ray Fluorescence (XRF) and Multi-Scan Core Logger (MSCL) core scanning analyses, the variation in water mass strength can be reconstructed and the suspension of the sediment based on Mass Accumulation Rates (MAR). In addition, the foraminifera assemblage will provide an estimate regarding the contemporaneous Sea Surface Temperatures (SST) relating to past climate changes. The analyses show that the overall MAR is lower during interglacial periods and high during glacial times. The MAR away from the PDE is much higher than near and on the PDE verifying that the PDE has regional hydrodynamics superimposed on the climatic variations. This reduced amount of MAR near the PDE is favourable for CWC growth as they will not be covered by sediment. Though, not all places near the PDE are favourable for CWC like the location between the drift mound and the PDE as sediment transport is limited by the flanks on both sides. CWC normally grow in elevated wide open spaces where the catchment of sediment particles and erosion of the seafloor is increased. MD08-3228 at a plateau behind the PDE offers the best location for coral growth, based on Mass Accumulation Rates as it provides enough sediment to build up the mound, but not to cover the corals. There is however a period of mass-wasting, which is negative to coral growth. Overall the demise in CWC from the LGM is due to a different hydrodynamic regime that provides a less suitable environment during glacial periods than before the LGM.