UC Irvine

We report marine dissolved organic carbon (DOC) ?14C from seawater collected from the North central Pacific Ocean (NCP) in 2015. These measurements show DOC ?14C 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 δ14C profiles from the NCP in 1985 and 1987 reveals that deep DOC δ14C values have decreased. We discuss several possible mechanisms that could cause such a shift in DOC δ14C values, including spatial inhomogeneity and temporal variability due to changes in the dissolution and δ14C value of surface derived particles in the deep sea. We find that forthcoming profiles of DOC δ14C results from the NCP will determine the primary mechanisms controlling deep DOC δ14C distributions, and changes over the past three decades.