Organic matter mineralization and the effects of petroleum pollution in a shallow-marine sediment - a case study from Århus Bugt, Denmark

Organic geochemical analyses of core samples from the Station 6 site in Århus Bugt, Denmark, show systematic changes with depth below the sediment-water interface. Over the upper 6-7 centimetres, corresponding to the deposits of the last 25-30 years, mineralization of organic matter is manifest in decreasing TOC, increasing C\/N and Hydrogen Index, changes in pyrolysate compositions, and in fatty acid distributions. Calculated losses of organic carbon due to microbial sulphate reduction show a close correspondence to measured values, supporting the important role of this process in organic matter mineralization. Below 6-7 cm, steady state sedimentation apparently has been disturbed, probably due to the excavation of a nearby navigation channel in the 1960-ties. Analyses of saturated hydrocarbons, including triterpane and aterane biological markers, point to a mixed origin for this group of compounds, comprising a dominant contribution from anthropogenic petroleum pollution, and a minor contri- bution from indigenous organic matter.