Acid digestion on river influenced shelf sediment organic matter: Carbon and nitrogen contents and isotopic ratios.

We show that acid type did not significantly affect results. We also find that (i) glacial and interglacial samples do not react similarly to acid pre-treatment, (ii) high acid strength (>1.5 mol.L-1 ) induces significant bias on δ13 Corg and TOC values, and therefore on C/N ratios; (iii) 25% of an isotopically distinct pool of organic carbon was lost when using acid concentrations of 0.2-1.5 mol.L-1 , affecting δ13 Corg values by more than 1.5‰; and (iv) geochemical evidence indicates that the leachable organic carbon pool is preferentially composed of terrestrial organic matter. These findings call for precautions when using C/N ratios and associated δ13 Corg values for paleo-environmental and climate reconstructions.