Department of Earth System Science

We report radiocarbon measurements of dissolved inorganic carbon (DIC) in surface water samples collected daily during 12 cruises to Station M in the northeast Pacific off central California. Individual surface ∆14C values ranged from 22‰ to 70‰ over 10 yr. Variability of average cruise values is highest during winter likely due to increased mixing. A general decrease of ∆14C values was observed at a rate of about 3‰ per year between 1994 and 2004, about half of that in atmospheric CO2 during this period (Levin and Kromer 2004). The ∆14C results ranged from 2-18‰ during individual cruises and were often significantly larger than the total uncertainty for individual measurements (±3.9‰). This indicates that a single ∆14C result from a surface site is not sufficient to capture the true variability of ∆14C in the surface ocean.