Variability of Dissolved Inorganic Radiocarbon at a Surface Site in the Northeast Pacific Ocean

Abstract

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  14 C 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  14 C values was observed at a rate of about 3‰ per year between 1994 and 2004, about half of that in atmospheric CO 2 during this period (Levin and Kromer 2004). The  14 C 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  14 C result from a surface site is not sufficient to capture the true variability of  14 C in the surface ocean.

Comparison of Particulate Organic and Dissolved Inorganic Radiocarbon Signatures in the Surface Northeast Pacific Ocean

“…This average POC  14 C value is slightly lower than the average of all DIC  14 C values determined during the same study (Table 1; 47 ± 14‰; Druffel et al 2010). Model II (geometric mean) regression analysis of all average POC and DIC  14 C values resulted in a weak correlation (Figure 2; R 2 = 0.11, p = 0.0287).…”

“…Surface seawater samples were collected for DIC at the same time as that for the POC samples using a bucket as described previously (Druffel et al 2010). POC particles were collected with a 33-µm mesh phytoplankton net using a clean, glass cod-end (250 mL).…”

“…A summary of individual and averaged POC  14 C values are shown together with contemporaneous DIC  14 C values (Druffel et al 2010) in both Table 1 and Figure 1. Individual  14 C values ranged from -82‰ to 66‰.…”

“…With the ultimate goal of testing the hypothesis that  14 C signatures of POC approximate those of DIC, here we report  14 C measurements of POC and DIC (Masiello et al 1998;Druffel et al 2010) samples collected from the surface water during 10 cruises from 1995-2004 in the northeast Pacific.…”

“…Here, we report ∆14C measurements of surface POC samples and compare them with contemporaneous DIC ∆14C measurements from the northeast Pacific Ocean (Hwang et al 2004;Druffel et al 2010). Samples were collected from surface waters at Station M off California between 1995 and 2004.…”