Determination of pore-water dissolved organic carbon fluxes from Mexican margin sediments

Holcombe, Brook L., Richard G. Keil, Allan H. Devol

Limnol. Oceanogr., 46(2), 2001, 298-308 | DOI: 10.4319/lo.2001.46.2.0298

ABSTRACT: Sediment dissolved organic carbon (DOC) fluxes were determined in the oxygen minimum zone along the north-western Mexican margin using five different methods: in situ benthic chambers, on-deck incubations, slicing, dialysis sampling (peepers), and sipping. For each of the five methods, replicates (n = 6-12) were made. Directly determined fluxes (whole-core incubations and benthic chambers) and calculated fluxes (sliced and dialysis-sampled cores) agree well (0.41 ± 0.09, 0.36 ± 0.04, 0.25 ± 0.05, and 0.25 ± 0.05 mmol C m-2 d-1, respectively). On the Mexican margin, the DOC flux was 8% of the sedimentary carbon input, suggesting that it is a significant component to the local carbon budget. Extrapolations of this flux to the total global margin suggest that shelf and slope sediments contribute 96 Tg C yr-1. The residence time of oceanic DOC based on this flux is consistent with measurements of the deep-water DO 14 C age. Profiles were also constructed from sip-isolated pore waters and yield consistently lower DOC profile gradients and DOC fluxes (0.06 ± 0.02 mmol C m-2 d-1). We propose that the consistently observed discrepancy between sip-isolated profiles and other isolation techniques is a result of sampling different reservoirs of pore water present in the heterogeneous sediment matrix.

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