Towards understanding global variability in ocean carbon-13

We include a prognostic parameterization of carbon-13 into a global ocean-biogeochemistry model to investigate the spatiotemporal variability in ocean carbon-13 between 1860 and 2000. Carbon-13 was included in all 10 existing carbon pools, with dynamic fractionations occurring during photosynthesis, gas exchange and carbonate chemistry. We find that ocean distributions of δ¹³C_DIC at any point in time are controlled by the interplay between biological fractionation, gas exchange, and ocean mixing. In particular, the deep ocean δ¹³C_DIC is sensitive (by > 0.5‰) to the degree of ocean ventilation. On interannual timescales, although the variability in δ¹³ C_DIC is a first order function of the atmospheric δ¹³CO₂ and overall carbon flux, the spatial distributions are controlled by the degree to which surface waters are exposed to the atmosphere. The δ¹³C_POC is highly sensitive to the species of inorganic carbon assimilated during photosynthesis (by 10 to 17‰), as well as the intrinsic growth rate and in SAU [CO₂(aq)], suggesting that phytoplankton utilize both HCO₃^- and CO₂(aq). The relationship between Δ¹³C_DIC and anthropogenic carbon (C_ant) varies by ± 70% regionally and circulation and biotic effects can influence estimates of C_ant that are based on Δ¹³C_DIC.