Towards understanding global variability in ocean carbon-13

International audienceWe include a prognostic parameterization of carbon-13 into a global oceanbiogeochemistry 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 d 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 d 13 C DIC is sensitive (by > 0.5%) to the degree of ocean ventilation. On interannual timescales, although the variability in d 13 C DIC is a first order function of the atmospheric d 13 CO 2 and overall carbon flux, the spatial distributions are controlled by the degree to which surface waters are exposed to the atmosphere. The d 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 [CO 2 (aq)], suggesting that phytoplankton utilize both HCO 3 À and CO 2 (aq). The relationship between Dd 13 C 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 Dd 13 C DIC