Abstract
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 Δ14C 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 Δ14C 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 Δ14C 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 Δ14C result from a surface site is not sufficient to capture the true variability of Δ14C in the surface ocean.
Highlights
Radiocarbon levels in dissolved inorganic carbon (DIC) of non-polar surface ocean waters were approximately 4–7% lower than CO2 in the pre-bomb atmosphere, causing a reservoir age of ~300– 600 14C yr in mixed layer DIC
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
We report daily surface DIC 14C values obtained for 12 cruises to Station M (Stn M), a high-productivity site located 220 km west of Point Conception, California
Summary
Radiocarbon levels in dissolved inorganic carbon (DIC) of non-polar surface ocean waters were approximately 4–7% lower than CO2 in the pre-bomb atmosphere, causing a reservoir age of ~300– 600 14C yr in mixed layer DIC. Temporal variability of the reservoir age at a given location in the surface ocean has been studied using seasonal and monthly coral skeletons (Brown et al 1993; Guilderson et al 2000) and daily surface water samples collected at sea (McDuffee and Druffel 2007; Druffel and Griffin 2008). Measurements of surface seawater in the Sargasso Sea during June 2000 indicated a change in water mass that was coincident with an increase in variability of 14C values (McDuffee and Druffel 2007) halfway through the cruise. Druffel and Griffin (2008) showed that daily sampling at 3 locations (north central Pacific, Sargasso Sea, and Southern Ocean) over the course of 2 4 week periods revealed surface 14C values that varied by 11 30‰, more than the total uncertainty of the measurement (7.8‰, 2 ) during all 6 cruises.
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