We report radiocarbon measurements of dissolved inorganic carbon (DIC) in surface water samples collected daily during cruises to the central North Pacific, the Sargasso Sea and the Southern Ocean. The ranges of Δ 14 C measurements for each cruise (11-30‰) were larger than the total uncertainty (7.8‰, 2-sigma) of the measurements. The variability is attributed to changes in the upper water mass that took place at each site over a two to four week period. These results indicate that variability of surface Δ 14 C values is larger than the analytical precision, because of patchiness that exists in the DIC Δ 14 C signature of the surface ocean. This additional variability can affect estimates of geochemical parameters such as the air-sea CO 2 exchange rate using radiocarbon.