Composition and degradation of organic matter in sediments from the Peru-Chile upwelling region

The biogeochemistry of surface sediments from the shelf and continental slope off Peru and Chile was studied in order to characterize factors and processes that control rates and extent of remineralization and burial of organic carbon in marine sediments. Elemental, isotopic, and molecular organic geochemical compositions showed that the sedimentary organic matter was predominantly derived from the highly productive surface waters in this region. Both established and newly evolved quality indicators were applied to assess organic matter freshness. Microbial degradation rates were related to organic matter freshness, providing evidence for a strong control of bioavailability on early diagenetic degradation processes. The presence of individual bacterial species could be traced by the identification of specific biomarker compounds. Abundance and distribution of bacterial cell wall constituents showed that bacteria were an important source of sedimentary organic matter and that remnants of bacteria persist in the sediments after the cell death.