Mediterranean functioning and sapropel formation: respective influences of climate and hydrological changes in the Atlantic and the Mediterranean |
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| Institution: | 1. The Institute of Earth Sciences, The Hebrew University of Jerusalem, Israel;2. Department of Marine Biology, Haifa University, Israel;3. School of Earth and Environment, Leeds University, Leeds, UK;1. Natural History Museum, University of Oslo, Pb. 1172 Blindern, 0318 Oslo, Norway;2. Centre for Earth Evolution and Dynamics (CEED), Pb. 1028 Blindern, 0315 Oslo, Norway;3. Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China;3. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China |
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| Abstract: | During Ocean Drilling Program (ODP) Legs 160 and 161, sapropels were recovered both in the western and eastern Mediterranean. This obliges to a reassessment of the previous studies focused on sapropels from only the eastern Mediterranean, and to consider the changes which occurred in the Mediterranean climate but also in the water characteristics both in the Atlantic and in the western Mediterranean. In the North Atlantic, the position of the polar front which migrated southwards during glacial times and the melting of northern ice caps during interglacial periods, together with the convection in the Labrador and Norwegian Seas, appear essential to control the salinities of the waters facing the Strait of Gibraltar. The salinities of the surface and intermediate layers constitute the first driving force of the Mediterranean dynamics, the second driving force being the Mediterranean climate. The stagnation of deep waters leading to sapropel deposition in the western Mediterranean may be explained by a drastic weakening of the density difference between Mediterranean outflow and Atlantic intermediate waters facing the Strait of Gibraltar. This weakening was induced primarily by the salinity decrease of Atlantic surface water and secondly by a rather high salinity in the Atlantic intermediate layer, rather than by a drastic deterioration of the Mediterranean climate. This scenario probably concerns most of the sapropel events and it may be used for the knowledge of Atlantic and Mediterranean functioning over climatic changes. |
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