Recent Sediment Layers Research Articles

Early diagenesis of trace metals used as an indicator of past productivity changes in coastal sediments

In sediments of Kiel Bight, which differ significantly in their redox-states and the rates of C org degradation, depth profiles of both dissolved and solid-phase Fe, Mn, Cd, Cu, Ni, and Co were measured. Porewater fluxes of Cd, Cu, and Ni were significantly higher at shallower (more oxic) stations as compared to highly reducing deeper subthermocline sediments while Mn fluxes behaved the opposite way. When normalized to Fe for grain size correction the measured solid-phase metal contents revealed that the high porewater flux has led to a near surface depletion of Mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic Cd in more oxic sediments. This difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling. Contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations. Thus, at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for Mn and higher for Cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years. This change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent C org input to the sediment due to eutrophication which accompanied industrialization.

Recent sedimentary history of Lake Monona, Wisconsin

Chemical analyses from two short cores in Lake Monona show that pronounced changes in chemical stratigraphy have occurred since white man moved into Madison and southern Wisconsin and began modifying the area. Since the mid to late 1800's, there has been an appreciable increase in P, Fe, Mn, Al, and K in the uppermost sediments. Maximum concentrations of P were observed near the turn of the century and in the most recent sediment layers.