Stored surface seawater originally collected in the North Sea was amended with dissolved organic matter (DOM) obtained from the diatom Skeletonema marinoi by exposing the diatom culture to a hydrostatic pressure level of 40 MPa for 24 h. To this end, S. marinoi had been grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. Diatom-cell-free DOM was added to aliquoted seawater samples at initial concentrations of 250 µmol C/L. The microbial degradation of the added DOM and the microbial response to DOM-amendment at 15°C and in darkness was followed for 2 weeks. The seawater was subsampled at defined time intervals to analyze a number of variables.

Information about the used cultured organisms:Skeletonema marinoi, Bigelow National Center for Marine Algae and Microbiota, Strain No. CCMP1332, isolated from Long Island Sound (41.2264 N, -73.0639 W) (isolation date is unknown); https://ncma.bigelow.org/CCMP1332