Our understanding of marine biogeochemical cycling in the ocean is still rather rudimentary. Recent analytical methods allow for unprecedented characterization of the diversity of organic molecules in the ocean. Similarly, the application of –omics techniques (metagenomics, -transcriptomics and –proteomics) allow obtaining insights into the functional diversity of microbial communities thriving throughout the oceanic water column. However, it is uncommon to find chemical analyses of organic molecules and the –omics approaches been directly performed on the same samples. Moreover, gene or protein abundance do not provide information on turnover rates of specific organic molecules. Hence, a combination of approaches is required to fully understand marine biogeochemical cycles, combining the characterization of dissolved organic matter with the functional diversity of microbial communities and linking this to bulk measurements of microbial activity. That way it would be possible to mechanistically understand the role of microbial communities in the biogeochemical cycling of the present and future ocean. This session should bring together scientists from the fields of marine biogeochemistry and microbial oceanography, with topics ranging from the transformation of individual organic molecules to bulk dissolved organic matter pool and from functional characterization of single microbial cells to basin-scale variation.