We have developed a ~45 year carbon isotope record (δ13C, Δ14C) from the coralline sponge Acanthochaetetes wellsi from Vanuatu in an effort to examine air-sea CO2 exchange using both the δ13C Suess effect and the bomb-14C transient. From 1953 to 1999 δ13C decreased by 0.9?. Pre-bomb Δ14C is -59?, consistent with coral based estimates from the same region and the post-bomb maximum (+121?) is achieved in 1973. A 1-D box-diffusion model was employed to quantify vertical diffusivity and air-sea exchange rates. The model suggests that a low vertical diffusion rate (0.1 cm2 s-1) coupled with a moderate CO2 exchange rate produces the overall observed shape of the pre-post bomb Δ14C record and the general large scale features of the δ13C time series. These parameters are on the low end of values used in ocean-carbon GCMs but are consistent with microscale tracer experiments.