Carbonate removal by acidification causes loss of nitrogenous compounds in continental margin sediments

This study reports on measurements of organic carbon (C-org) and total nitrogen (N-tot) in surface sediments originating from 6 transects along the northwest European continental margin. After elimination of carbonates by an acidification technique using sulphurous acid, both elements were analysed in the same sediment sample using an elemental analyser. C-org and N-tot in the sample were comparatively low, ranging between 1 and 10 mg C and 0.2 to 1 mg N g(-1) dry sediment. In a second analysis, the samples were analysed without acid addition, resulting in N-tot concentrations of 0-50% higher compared to their acidified counterparts. As a consequence, molar C/N ratios derived from the analysis of C-org and N-tot in the acidified sample ranged between 6 to 11, while the N-tot separate analysis reduced C/N ratios to 6 to 8. It is suggested that the addition of sulphurous acid to eliminate inorganic carbon volatilises nitrogenous organic matter. (C) 2000 Elsevier Science B.V. All rights reserved.