engleski

Trace elements in recognition of sources and diagenetic processes in marine sediments

The aim of the lecture is to provide information about the processes which regulate geochemistry and early diagenesis of trace elements in marine sediments. Distribution of major elements and trace elements which are constituents of main sediment components (for example Al, K, Li) illustrates composition and origin of the sediment. Most of other trace elements are transferred from the solution to sediments by adsorption onto suspended particulate matter which is deposited on the seafloor. Upon reaching the seafloor, particulate matter is subject to physical and chemical changes collectively referred to as diagenesis. Most diagenetic chemical changes are driven by redox reactions, which involve the oxidation of organic matter. As results, suboxic and anoxic conditions are formed in marine sediments. These conditions have a profound effect on the chemistry of trace metals, their distribution between solid and dissolved phase and consequently, their mobility in sediments. Diagenetic processes are especially important for elements which chemical speciation is redox dependant, such as for example Fe, Mn, Mo and U. Some of those elements (Mo) become enriched under anoxic conditions and can serve for reconstructing the redox conditions in the water column at the time of sediment deposition. A special case of chemical diagenesis is microbiological methylation of mercury in sediment, which is of the great significance for the entire biogeochemical cycle of Hg in the environment. Data from several coastal areas of the Croatian Adriatic coast (the Krka river estuary, the Kaštela bay, and especially saline lakes at the Island Mljet) will be used for illustration. Distribution of major and trace elements in sediments and porewater will be presented and geochemical behavior of these elements will be discussed.

Sediment; geochemistry; trace elements

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