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CONTRIBUTIONS to SCIENCE, 5 (1): 25–39 (2009) Institut d’Estudis Catalans, Barcelona DOI: 10.2436/20.7010.01.57 ISSN: 1575-6343 www.cat-science.cat research reviews The Mediterranean: a synoptic overview Carles Bas* Institute of Marine Sciences, CSIC, Barcelona, Spain Member of the Biological Sciences Section of the IEC Member of the Royal Academy of Sciences and Arts of Barcelona Resum. S’explica de forma breu la formació de la Mediterrània Abstract. The formation of the Mediterranean Sea from the a partir del Tethys així com tota l’estructura geomorfològica former Tethys, and its geomorphological structure, with spe- amb especial referència a la orogènia alpina. Especial atenció cial reference to the Alpine orogenesis, are discussed. Spe- es dedica a la circulació superficial d’origen atlàntic considera- cial attention is given to the superficial circulation originating da com el factor bàsic de tota la dinàmica mediterrània, amb from the Atlantic, an essential factor in the Mediterranean’s especial referència al paper dels estrets i al significat de l’efecte dynamics. Particular reference is made to the role of the sea’s estuarí. Així mateix l’acció dels vents més importants es té en straits and to the significance of the estuary effect. Further- compte pel fet que afecta la dinàmica complexa oceanogràfi- more, the action of the more important winds is considered ca. Com a primer resultat del conjunt de les accions dinàmi- insofar as they affect the Mediterranean’s complex oceano- ques s’estudia i es reflexiona sobre els diferents factors que graphic dynamics. The dynamic actions of these winds are contribueixen a la productivitat mediterrània considerada su- analyzed, as are the different factors contributing to the Medi- perior a l’esperada. En un altre aspecte s’examinen les carac- terranean’s higher than expected levels of productivity. The terístiques de l’ecosistema mediterrani considerat com a una characteristics of the Mediterranean ecosystem are also ana- gran unitat encara que amb gradients molt característics. Com lyzed from a different perspective, by considering the Mediter- un dels elements que caracteritzen a l’estructura dinàmica de ranean ecosystem as a single large unit, although the existence l’ecosistema mediterrani es revisa la influència de l’home a tra- of very characteristic gradients is recognized. The disrupting vés de la pesca i la contaminació en tant que factors pertorba- influence of humans, through fishing and contamination, is dors. Finalment com a resum s’exposa una visió global en la acknowledged as one of the elements influencing the dynam- que s’assaja d’integrar els factors oceanogràfics, biològics, ic structure of the Mediterranean ecosystem. Finally, as a socioeconòmics amb especial atenció a la dinàmica humana summary, a global view is put forward that seeks to integrate amb l’intent que la integració de tots aquests aspectes perme- oceanographic, biologic, and socioeconomic factors with hu- ti una comprensió de la totalitat de la problemàtica mediterrà- man dynamics. The goal is to integrate these disparate as- nia com a base d’una possible planificació més sostenible. pects into a unified, broad-ranging comprehension of the Mediterranean that will serve as the grounds for more sus- Paraules clau: Mediterrània · productivitat marina · tainable planning. ecosistemes marins · impacte dels humans en la pesca Keywords: Mediterranean · sea productivity · marine ecosystems · human impact on fisheries Presentation own distinct characteristics but with a common denominator related to their origin. Today, the best-preserved remnant of Origin. The displacement of the emerged land mass Pangea the Tethys Sea is the Mediterranean Sea, which except for a towards the northern part of the terrestrial globe led to the ap- narrow strip is completely enclosed by land. In this context, it is pearance of a ring-shaped sea, known as the Tethys Sea, that necessary to consider another distinct body of water, the Para- practically surrounded the planet. The contours of this ring tethys, whose relationship to the Mediterranean changed over blurred during subsequent geological periods, giving way to time and is poorly understood (Fig. 1). The difficulty lies in the newly formed land masses and bodies of water, each with its fact that while the Mediterranean has a very high salinity, the salinity of the Paratethys was almost zero. It consisted of a large continental basin that Central and Southern Europe, all * Correspondence: Carles Bas, Institut de Ciències del Mar (ICM- the way to Central Asia. Today, its remains are the Black, Cas- CSIC), Passeig Marítim de la Barceloneta, 37–49, E-08003 Barcelona, Spain. Tel. +34-932309500. Fax +34-932309555. Email: carlesbas@ pian, and Aral Seas. During the Pliocene, 5.5 millions years hotmail.com ago, the straits of Istanbul (Bosporus) and the Dardanelles 001-128 Contributions 5-1.indd 25 25/11/2009 10:26:11 26 Contrib. Sci. 5 (1), 2009 Bas Gabes and Sirte. The alpine movements that determined the Mediterranean’s structure have had important political conse- quences for centuries, with particular significance in the west- ern and north-central areas of this region. The Anatolian Penin- sula, with its very ancient central nucleus, also has margins of alpine origin. The Mediterranean’s alpine orogeny accounts for its narrow continental shelves, its abrupt or poorly developed coastlines, and its continental slopes, with their numerous sub- marine canyons. In addition, it consists of several vast plat- Fig. 1. Simplified diagram of the Sarmatic Sea (Paratethys). forms, some of which correspond to extensive coastal terres- trial zones. These latter structures account for many of the Mediterranean’s oceanographic characteristics, in terms of the opened flow towards the Mediterranean; this, in turn, affected sea’s unique marine biology, and thus to the density of human the surrounding areas, especially the northern Aegean Sea. Al- settlements, which have long benefited and depended on fish- though the hydrographic and—to a certain extent–biological ing from its waters (Fig. 2) [3]. characteristics of the Black, Marmara, and Azov (Pontic region) The most extensive platforms are found in the Castelló- Seas are in many ways distinct from those of the Mediterrane- València zone, in the Gulf of Lion and the Rhone River delta, the an, these bodies of water can still be considered in the context northern Adriatic, the Gulf of Gabe, and in the Black Sea, in the of the Mediterranean [1,2]. vast zone between the mouth of the Danube and the Crimean Alpine orogenic movements were of great importance in the Peninsula. The latter shelf is partly formed by sedimentary con- origin of the Mediterranean basin. Not only did they determine tributions from southeastern European rivers, i.e., the Dnieper its structural morphology but also, when the Strait of Gibraltar and Dniester, together with the Don, which flows into the small opened, some 5 million years ago, were associated with a bi- Sea of Azov. otic recolonization of Atlantic origin. These resulted in the cur- Along with the Mediterranean’s narrow continental shelves, rent biological structure and reflected extremely important another remarkable feature is the numerous canyons distrib- changes that modified the primitive biotic populations. Traces uted throughout the talus. While some of the canyons are oro- of the successive invasions that took place over several geo- genic in origin, the majority represents the continuance of flu- logical periods can still be identified in the current biotic popu- vial basins, which have deeply marked particularly the upper lations. part of the continental talus. These basins have been influ- enced byvariations in sea level as well as by the Messinian Salinity Crisis, which reduced the Mediterranean to a few la- Geomorphologic structure goons. Of equal importance are the three active tectonic plates The current, definitive structure of the Mediterranean reflects whose contact zones are located in the Mediterranean: the Af- the most recent orogenic processes, i.e., the Alpine orogeny. rican plate, the Eurasian plate and the Arabian plate, the latter Globally, the Mediterranean is a basin that extends latitudinally being responsible for delimiting the sea’s most eastern part. and is located in the temperate zone of the northern hemi- The activity of the two former plates not only gives rise the sphere. While the northern Mediterranean has a very sinuous Mediterranean’s alpine orogeny, but also to earthquakes and structure, with three land formations–the Iberian, Italian and to volcanic areas, both of which occur approximately along a Balkan Peninsulas—that extend southwards, the southern line that crosses the Mediterranean from west to east. This line coast is practically rectilinear, broken up only by the gulfs of also marks the location of the Mediterranean Islands, the Bal- 45 40 35 -5 0 5 10 15 20 25 30 35 40 Fig. 2. Map of the Mediterranean and Pontic Basins. Isobathytherms of 200 m and 1000 m. 001-128 Contributions 5-1.indd 26 25/11/2009 10:26:14 The Mediterranean: a synoptic view Contrib. Sci. 5 (1), 2009 27 earic Islands, Corsica, Sardinia, Sicily, Malta, Crete and Cy- prus. All of these islands are related to orogenic movements that disrupted the Mediterranean basin. Also of note are a group of islands of different origin located in the Aegean Sea. These islands arose through Tertiary and Quaternary collapse/ subduction processes that allowed for the appearance of the Aegean Sea and its mountainous remainsthe islands. The Mediterranean’s straits are another important geomor- phologic feature, not only because they join or separate the different Mediterranean sub-basins but also because they are Fig. 3. Proposed Mediterranean subbasins. the points of passage of masses of water and thus greatly influ- ence the sea’s oceanographic dynamics [4]. Undoubtedly, the most important are the Strait of Gibraltar, which re-establishes Table 1.