Metal diagenesis in a shallow semi-enclosed marine system in the Aegean Sea, Greece

Trace metal and organic carbon distributions were examined in core sediments of Kalloni Bay during September 2000 in order to examine the diagenetic process and its impact on metal mobility. Solid sediment profiles show significant variations in Mn, Fe and Ni concentrations between sampling stations due to geological background variability and diagenetic processes in the sediment (for Mn). Solid phase organic carbon profiles reflect episodic input of organic matter from the land. The redox status of the sediments can be characterized from sub-oxic to anoxic, leading to dissolution of Mn oxides and enhancement of dissolved Mn at the surface sediment layers of the Bay. Dissolved Fe maximal concentrations were located at a sediment depth of few centimetres below the Mn maximum. Nickel distribution was mainly influenced by the geological background of a part of the Bay's watershed consisting of ultrabasic minerals. Partition coefficients between solid phase and porewater (Kds) indicated the increase mobility of Mn (and to a lesser degree of Ni and Zn) in the upper sediment layers. Concentrations Factors indicated that metals (especially Mn and Zn) may flow from porewater to the overlying seawater because of concentration gradients.