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Aged black carbon identified in marine dissolved organic carbon

Produced on land by incomplete combustion of organic matter, black carbon (BC) enters the ocean by aerosol and river deposition. It has been postulated that BC resides in the marine dissolved organic carbon (DOC) pool before sedimentary deposition and may attribute to its great 14C age (1500–6500 14C years). Here we report the first radiocarbon measurements of BC in high molecular weight DOC (UDOM). BC exported from rivers is highly aromatic and <500 14C years old, while open ocean samples contain less aromatic BC and have an age of 18,000 ± 3,000 14C years. The low abundance of BC in UDOM (0.5–3.5%) suggests that it is more labile than presently believed and/or the low molecular weight DOC contains a larger proportion of aged BC.