Ramped pyrolysis oxidation (RPO) carbon isotope data from DOC in water samples collected during R/V Western Flyer Benthic-Pelagic Coupling expedition to Station M in the eastern Pacific Ocean in April 2018

The >5000-year radiocarbon age (14C-age) of much of the 630±30 Pg C oceanic dissolved organic carbon (DOC) reservoir remains an enigma in the marine carbon cycle. The fact that DOC is significantly older than dissolved inorganic carbon (DIC) at every depth in the ocean forms the basis of our current framing of the marine DOC cycle where some component persists over multiple cycles of ocean mixing. As a result, 14C-depleted, aged DOC is hypothesized to be present as a uniform reservoir with a constant 14C signature and concentration throughout the water column. However, a key requirement of this model would be direct observations of DOC with similar 14C signatures in the surface and deep ocean. To address this data gap, we applied a thermal fractionation method to investigate DOC in water samples collected from a range of water column depths during the R/V Western Flyer cruise to Station M off the coast of central California in April 2018. This dataset presents carbon isotope data for both bulk samples and samples processed using ramped pyrolysis oxidation (RPO) procedures.