The global total amount of dissolved organic carbon (DOC) stored in marine DOM is larger than all carbon in living land plants and 30-times larger than all carbon in marine animals, plants, bacteria and organic particles combined. DOM serves as a buffer in the organic carbon cycle, and complexation with heavy metals changes their solubility, distribution and toxicity. Despite its importance and abundance the chemical composition of DOM is largely unknown. The aim of our studies is the molecular chemical characterization in order to identify specific sources (e.g. marine, terrestrial, sea ice) and transformation processes (e.g. microbial and photo degradation).

Recent improvement in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was a great step forward to approach this aim. FT-ICR-MS detects exact masses for single intact molecules. Extremely high resolution allows differentiating between molecules with a weight difference of less than one electron. From the exact masses molecular formulas can be assigned. Each FT-ICR-MS analysis provides thousands of molecular formulas in each natural organic matter sample. This is the basis to look for specific molecules which can be used as tracers for different sources or processes. These tracers can improve our knowledge about the fluxes and the fate of DOM.