New Radiocarbon Constraints on the Global Cycling of Solid‐Phase Extractable Dissolved Organic Carbon

Abstract

AbstractRadiocarbon (∆14C) measurements suggest the deep ocean stores marine dissolved organic carbon (DOC) on millennial timescales. The mechanisms that mediate this residence time remain unconstrained. Solid‐phase extraction (SPE) has emerged as a widely used technique to isolate DOC for subsequent analyses. We present SPE‐DOC concentrations and ∆14C values for three GO‐SHIP Repeat Hydrography transects, spanning the Pacific, Southern and Indian Oceans. Comparisons of SPE‐DOC with total DOC ∆14C values are used with an isotopic mass‐balance to estimate the size of the refractory DOC (RDOC) reservoir and changes in RDOC relative abundance in the global ocean. Estimated RDOC abundance is similar across the deep Pacific and Indian Oceans (average = 93 ± 5%, 35 ± 6 μM), whereas RDOC in the surface ocean varies as a function of total DOC concentration. Our results fill in spatial SPE‐DOC ∆14C sampling gaps for the global ocean, and our mass‐balance RDOC estimates are consistent with previous observations.