Temporal Variability of Dissolved Organic Radiocarbon in the Deep North Pacific Ocean

We report marine dissolved organic carbon (DOC) ∆ 14 C from seawater collected from the North central Pacific Ocean (NCP) in 2015. These measurements show DOC ∆ 14 C values averaged –235±5‰ ( n =3) in the mixed layer (24–81 m) and –544±5‰ ( n =5) in the deep water (1500–5139 m). A comparison of these data with two previously published DOC ∆ 14 C profiles from the NCP in 1985 and 1987 reveals that deep DOC ∆ 14 C values have decreased. We discuss several possible mechanisms that could cause such a shift in DOC ∆ 14 C values, including spatial inhomogeneity and temporal variability due to changes in the dissolution and ∆ 14 C value of surface derived particles in the deep sea. We find that forthcoming profiles of DOC ∆ 14 C results from the NCP will determine the primary mechanisms controlling deep DOC ∆ 14 C distributions, and changes over the past three decades.