Constraining the 2-component model of marine dissolved organic radiocarbon

Keeling plots of dissolved organic carbon (DOC) concentration and Δ¹⁴C depth profiles imply rapid, diapycnal transport of DOC to the meso- and bathypelagic zones, but do not constrain the mechanism of redistribution. We review the 2-component Keeling plot model, and present an alternative formulation explicitly based on homogenization of water parcels. Applying this new model to DOC and dissolved inorganic carbon (DIC) depth profiles suggests that the dominant controls on DOC redistribution differ throughout the water column. DOC concentration and Δ¹⁴C gradients were consistent with biogeochemical processing in the epipelagic and advection in the mesopelagic. Vertical gradients in DOC concentration and Δ¹⁴C were insufficient for further interpretation in the bathypelagic. Ultimately, additional concurrent measurements of DOC and DIC concentrations and Δ¹⁴C values throughout the water column at more locations are needed to constrain the applicability of two-component mixing models to marine DOC.