Abstract: The reactive-iron (Fe_R)-bound organic carbon (OC-Fe) in marine sediments has long-term preservation potential. Accurate determination of OC-Fe content is essential to evaluate its contribution to carbon sequestration (f_OC-Fe) and to global warming. Quantitative differences between the fumigation and rinse methods, applied to estimate the OC-Fe and f_OC-Fe, have not previously been assessed. In this study, the fumigation and rinse methods were used respectively to remove inorganic carbon of the original samples, after reduction experiment and control experiment for which samples are from 5 surface sediments in Prydz Bay, Antarctica. Then, the OC content was measured, and the OC-Fe content and f_OC-Fe were calculated. The OC content measured with the rinse method was 34.82%±12.92%, 32.80%±15.11% and 26.15%±20.51% lower than with the fumigation method in the raw, control and after reduction samples, respectively. This implies notable dissolution of acid-soluble and water-soluble OC with rinse method, resulting in an ineffective of the control experiment. The OC-Fe content and the f_OC-Fe values range obtained were significantly different between the two methods, indicating that the rinse method can partially dissolves OC bound with highly crystallized iron oxide or to low-activity iron silicate, thereby amplifying the f_OC-Fe differences, and preventing accurate assessment of the OC-Fe contribution to OC in marine sediment. Therefore, fumigation method is the recommended method to remove inorganic carbon in the study of OC-Fe.

Key words:

marine sediments, organic carbon, reactive iron, rinse method, fumigation method