Department of Earth System Science

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 the¹⁴C-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 and¹⁴C ages are correlated. Photochemical mineralization may therefore be an important control on the persistence of ¹⁴C-depleted DOC in the ocean.