Particulate organic carbon and nitrogen samples were acid fumed to remove inorganic carbon. Carbon and nitrogen content was measured in the course of stable isotopic analysis using a coupled elemental analyzer (Euroboprep), isotope-ratio mass spectrometer (Finigan MAT 251) system. Carbon and nitrogen mass was calculated from the corresponding, integrated ion beam intensities and standardized based on analysis of materials of known C and N content. Reference: M.A. Altabet, Limnology and Oceanography, 46(2), 368-380 (2001), doi:10.4319/lo.2001.46.2.0368.