Research focus of our group is the biogeochemistry of dissolved organic matter (DOM) in the ocean. Marine DOM plays a vital role for life on Earth. It links organic matter production and decay in the water column as products of primary production can only be taken up by microbial consumers as small dissolved molecules. Most of DOM is turned over by microorganisms within hours to days after production. A small fraction of DOM, however, resists rapid microbial degradation. This fraction has persisted in the ocean for thousands of years and has accumulated to the largest pool of organic carbon in the ocean, it contains more carbon than all living biomass on Earth combined. We consider DOM as the marine geometabolome, which is the entirety of small molecule metabolic products and their abiotic transformation products in the marine environment. Our main tools for studying the marine geometabolome are ultrahigh-resolution mass spectrometry (Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) and other chemical analytical approaches, combined with multivariate statistics and numerical modelling.