Ferromanganese concretions from the Baltic sea can be divided into three main types based on their abundance, morphology, composition and mode of formation; those from the Gulfs of Bothnia, Finland and Riga, from the Baltic Proper and from the western Belt Sea.Concretions from the Gulf of Bothnia are most abundant in Bothnian Bay where the abundance reaches 15-40 kg m -2 in an area of about 200 km 2. This is equivalent to about 3 million tonnes of concretions and has led to these deposits being evaluated as an economic resource. These concretions are mainly spheroidal up to 25-30mm in diameter and are formed in the uppermost water-rich sediment layers at well-oxidized sites. They are most abundant where sedimentation rates are <0.4 mm a -1 . In the Bothnian Sea, fiat crusts with low Mn/Fe ratios are widely distributed.Concretions from the Gulf of Finland are abundant in the eastern half of the gulf with a maximum abundance of 18-24kgm -2. One area of about 300 km 2 in the Russian sector of the gulf contains about 6 × 106 tonnes of spheroidal concretions and is receiving serious attention as an ore resource. These concretions frequently occur in the upper brown oxidized layer of the sediment.Concretions from the Gulf of Riga are most abundant (up to 17 kg m -2) around a central depression containing muddy sediments. Spheroidal concretions occur adjacent to the depression and discoidal concretions and crusts further away.Concretions from the Baltic Proper are found mainly around the margins of the deep basins in a depth range 48-103m. The concretions are mainly discoidal 20-150mm in diameter and crusts. Their abundance is mainly sporadic and more rarely common to abundant. Locally, abundances of 10-16 kg m -2 are attained. Their formation is the result of the build up of Mn and Fe in the anoxic waters of the deep basins of the Baltic Proper. During major inflows of North Sea water (> 100 km 3) into the Baltic which occur on average once every 11 years, the anoxic waters are flushed out of the basins. Mn and Fe percipitate out as an unstable gel and are ultimately incorporated into the concretions. The concretions occur mainly on lag deposits in the vicinity of the halocline where strong bottom currents Occur.

Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change.

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