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 delta(13) C-DIC at any point in time are controlled by the interplay between biological fractionation, gas exchange, and ocean mixing. In particular, the deep ocean delta(13) C-DIC is sensitive ( by > 0.5%) to the degree of ocean ventilation. On interannual timescales, although the variability in delta(13) CDIC is a first order function of the atmospheric delta(13) CO2 and overall carbon flux, the spatial distributions are controlled by the degree to which surface waters are exposed to the atmosphere. The delta(13) C-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 situ [CO2(aq)], suggesting that phytoplankton utilize both HCO3 -and CO2( aq). The relationship between Delta delta(13) C-DIC and anthropogenic carbon (C-ant) varies by +/- 70% regionally and circulation and biotic effects can influence estimates of Cant that are based on Delta delta(13) C-DIC.