A mechanism for the enrichment of Cu and depletion of Mn in anoxic marine sediments, Banweol intertidal flat, Korea

To understand the behaviour of heavy metals in anoxic marine sediments, surface and core sediment samples were collected in the Banweol intertidal flat (BIF) on the west coast of Korea where sulphate reduction occurs actively. Contents of Cu in this area are considerably higher than those in nearshore environments around the Korean peninsula, whereas those of Mn are lower. Copper in the sulphide fraction is enriched in the BIF sediments compared to that in the nearshore environments while Mn in the oxide fraction is depleted. Meanwhile, contents of Ni, Co, Pb and Cd in BIF sediments are comparable to those in the nearshore environments. The above results suggest that the precipitation of copper sulphide and the dissolution of manganese oxide are responsible for the enrichment of Cu and the depletion of Mn, respectively, in the highly anoxic BIF sediments. Hence, aratio of Cu/ Mn is regarded as an appropriate indicator of diagenetic influence in anoxic marine sedimentary environments.