Photochemical reactivity of ancient marine dissolved organic carbon

Marine dissolved organic carbon (DOC) is the largest reservoir of reduced carbon in seawater and persists up to 4,000-6,000 conventional radiocarbon (¹⁴C) years on average. Photochemical degradation has been suggested as a geochemical sink for these long-lived molecules, yet there have been no studies relating photochemical lability to the 14C-ages of surface DOC. We observed apparent second order (2°) kinetics with respect to DOC and a strong trend from Δ¹⁴C-enriched to depleted values during exhaustive photomineralization of surface marine DOC with high energy UV light. Geochemically, these results suggest that surface DOC is an isotopically- heterogeneous mixture of molecules for which photochemical lability and ¹⁴C ages are correlated. Photochemical mineralization may therefore be an important control on the persistence of ¹⁴C-depleted DOC in the ocean. Citation: Beaupré, S. R., and E. R. M. Druffel (2012), Photochemical reactivity of ancient marine dissolved organic carbon, Geophys. Res. Lett., 39, L18602.