Carbon Isotope Measurements of Surface Seawater from a Time-Series Site Off Southern California

Abstract

We report carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from a time-series site off the Newport Beach Pier in Orange County, California. These data represent the first time series of Δ14C data for a coastal southern California site. From a suite of samples collected daily from 16 October to 11 November 2004, Δ14C values averaged 32.1 ± 4.4‰. Freshwater input from the Santa Ana River to our site caused Δ14C and δ13C values to decrease. Since this initial set of measurements, a time-series site has been maintained from November 2004 to the present. Surface seawater has been collected bimonthly and analyzed for Δ14C, δ13C, salinity, and ΣCO2 concentrations. Water samples from the Santa Ana River were collected during the wet season. California sea mussels and barnacle shells, ranging from 4 to 6 months old, were also collected and analyzed. Results from May 2005 to January 2008 show no long-term changes in δ13C DIC values. Δ14C DIC values over the 2005–2006 period averaged 33.7‰; high Δ14C values were observed sporadically (every 6–7 months), suggesting the presence of open water eddies at our site. Finally, in 2007, a stronger upwelling signal was apparent as indicated by correlations between Δ14C, salinity, and the Bakun index, suggesting that the Δ14C record is an indicator of upwelling in the Southern California Bight.