The relationship between dissolved organic carbon (DOC) and fluorescence in anoxic marine porewaters: Implications for estimating benthic DOC fluxes

Fluorescence and dissolved organic carbon (DOC) measurements of porewaters from the Santa Barbara Basin, the Guaymas Basin, and the upper sections of the Nankai Trough suggest that ultraviolet fluorescence (λ_ex = 325 nm, λ_em = 450 nm) may be used as a first order estimate of DOC in anoxic marine porewaters. The majority of porewater organic carbon appears to be fluorescent, while a constant ~1 mM DOC, probably the low molecular weight compounds, is not fluorescent. These data are consistent with a model in which low molecular weight compounds dissolved in porewater act as the common intermediate between labile sedimentary organic matter and remineralization or polymerization products. Fluorescence may also be used to sensitively estimate benthic DOC fluxes to the overlying water column. Results from the Santa Barbara Basin, if representative of global anoxic oceanic regions, indicate that DOC release from anoxic sediments is not a major source of oceanic DOC when compared to internal recycling rates, but may be comparable to external input or permanent removal processes.