Organic matter in sediments and suspended matter is a complex mixture of constituents with different histories, sources and stabilities. To study these components in a suspended matter sample from the Ems-Dollard Estuary, we used combined molecular analysis with pyrolysis/gas chromatography/mass spectrometry and stable and radioactive carbon isotope analyses of the bulk and separated chemical fractions. Carbohydrates and proteins, ca. 50% of the total organic carbon (TOC), are much younger than the bulk sample and have a somewhat higher δ¹³C value. Lipids and the final residue are considerably older and have lower δ¹³C values. The final residue, ca. 17% of the total carbon, consists mainly of aliphatic macromolecules that could be derived from algae or terrestrial plants. The δ¹³C value points to a marine origin.