THE BALTIC SEA 5 120 THEThe B BalticALTIC Sea between SEA Poland and Sweden. (Photo: Lars Rydén.) “All pollutants that we pour into our small sinks at home will finally end up in our large common sink, the Baltic Sea.” Dr Andrzej Kowalczewski, Warsaw University, in a Baltic University TV broadcast. The Baltic Sea is the final recipient of pollutants from The Baltic Sea should also be saluted for its many the entire basin and is of special concern in efforts to positive aspects. Its short geological history of only a improve our environment. few thousand years after the last glaciation is the cause There are many reasons for being concerned. The of its many dramatic and beautiful sceneries. This Baltic Sea is an unusually sensitive water body, being includes the largest archipelago in the world with some unique in many ways. It is, surface-wise, one of the largest 25,000 islands between Sweden and Finland, and many brackish water bodies in the world; brackish means that it special coastal types. For similar reasons, the Baltic does not have marine water, as the oceans, or fresh water, Sea is also very productive, in fact one of the most like lakes, but has salt concentrations between the two. productive seas in the world, due to its comparatively As a consequence, there are comparatively few species large nutrient content. Fishing in the Baltic Sea has that have adapted to live in the Baltic Sea. This low level always been very important. of biological diversity makes it sensitive to impact. If one In this chapter, we will study the Baltic Sea itself. species is affected, there might be no other that can take This study is important in order to understand the fate over its role in the ecosystem. and effects of environmental impacts in the region and The Baltic Sea has an average depth of only about how to deal with them. The unique characters of the 50 metres. The reason is that, geologically speaking, it Baltic Sea will be highlighted and explained. Later on, is lying on a continent rather than between continents, it will be clear that the Baltic Sea is unique for several as do the several kilometre deep oceans. Therefore, other reasons. It is the best monitored water body in pollutants are not as diluted as in the oceans. In addition, the world, with 100 years of data available. It was the the water in the Baltic Sea has only a small passage to object of the first environmental co-operation between the large oceans via the Danish straits to the North Sea. the former Soviet Union and the West. In 1974, the The exchange with the oceans is thus restricted and Helsinki Convention and its Commission for the the half-life of its water is about 25 years. Pollutants protection of the Baltic Sea were created. In 1992, when stay in the Baltic Sea for a very long time. The turnover this convention was much improved and expanded, it of pollutants in the Sea is furthermore affected by its was made clear that 95% of the pollutants entering the position on northern latitudes. An oil spill in the southern sea come from the drainage basin and that it is where parts of the world may disappear rather quickly, but it action must be taken. Today, there is a very large takes much longer when all processes are slowed down investment programme in the drainage area to protect due to a cold climate. the Baltic Sea. Authors of this chapter Lars Håkanson, main text with contributions by Lars-Christer Lundin; Oleg Savchuk and Victor Ionov, the dynamic Baltic Sea; Stanislaw Musielak and Kazimierz Furmanczyk, the coasts of the TBalticHE Sea. BALTIC SEA 121 THE BALTIC SEA A SYSTEMS APPROACH TO THE BALTIC SEA What is so special about the Baltic Sea?..........................................................................................................................123 Outlook Box 5.1 The sixty seas of the world...................................................................................................................124 Maps of the Baltic Sea region ..........................................................................................................................................124 Functional zones ..............................................................................................................................................................127 THE BALTIC SEA WATER Water balance ...................................................................................................................................................................129 Surface water circulation .................................................................................................................................................129 The ice..............................................................................................................................................................................130 Three important parameters – salinity, temperature, and oxygen content .......................................................................131 Review Box 5.2 The dynamic Baltic Sea ........................................................................................................................132 Processes of coastal water exchange and mixing ............................................................................................................134 Methods Box 5.3 How to measure water exchange.........................................................................................................135 Climatic influences ..........................................................................................................................................................135 THE COASTS OF THE BALTIC SEA The coasts, a resource for many.......................................................................................................................................136 Coastal types – what the coast looks like ........................................................................................................................136 The coastal ecosystem is a complex web of interactions.................................................................................................137 Outlook Box 5.4 The Baltic Sea Coasts...........................................................................................................................138 The form of the coasts decides how they react to pollutants ...........................................................................................140 THE BOTTOMS Sediments and bottom types ............................................................................................................................................141 Three different functional bottom types ..........................................................................................................................141 Sediment Contamination..................................................................................................................................................142 Resuspension and land uplift ...........................................................................................................................................142 Laminated sediments and hydrogen sulphide ..................................................................................................................143 Methods Box 5.5 How to study bottom sediments ..........................................................................................................144 122 THE BALTIC SEA A SYSTEMS APPROACH TO THE BALTIC SEA What is so special about the Baltic Sea? The Baltic Sea accounts for almost a quarter of the Baltic Sea basin, and is of decisive importance to all the countries along its coasts. It is special in many ways. Firstly, the Baltic Sea is not similar to the deep oceans between the continents. Instead, it is situated on a continent, it is epicontinental. Other areas of this type are the Hudson Bay, the Persian Gulf, and the North Sea. These are all shallow seas, rarely more than 100 m deep, whereas the seas between continents are generally at least 2,000 m deep, e.g., the Mediterranean, the Black Sea, and the Red Sea. An epicontinental sea is more or less cut off from the oceans, it is semi-enclosed, as opposed to the so-called shelves, the not so deep areas on the Atlantic coasts. The Baltic Sea has only the narrow connection with the Atlantic through the Danish belts. Secondly, the Baltic Sea is a brackish water body, meaning that it is neither fresh water nor fully marine water, but with a salt concentration in between. This is one consequence of the semi-enclosed state of the Baltic Sea, it is neither a salt-water sea nor a lake. Brackish waters are rather unusual on Earth, and few animals and plants are adapted to live in them. A strong tidal range in the Kattegat would have increased the salt influx to the Baltic Sea to make it more marine, but the tide is only about 1-2 dm there. A tidal node preventing the tidal waves from entering the Kattegat is situated between Norway and Denmark. Thirdly, the Baltic is more nutrient rich than the oceans. This is mainly due to the post-glacial processes of land uplift. As the land rises, new bottom areas are exposed to waves. The nutrients bound to these old sediments are washed out in the sea and may, once again, be used by plankton and algae. Hence, the few species living in the Baltic Sea have an ample supply of food and they are generally present in large numbers. The fishing in the Baltic Sea is intense and of considerable economic importance.