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 ∆14C data for a coastal southern California site. From a suite of samples collected daily from 16 October to 11 November 2004, ∆14C values averaged 32.1 +/- 4.4. Freshwater input from the Santa Ana River to our site caused ∆14C and 13C 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 ∆14C, delta-13C, salinity, and sigma-CO2 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 delta-13C DIC values. ∆14C DIC values over the 2005-2006 period averaged 33.7; high ∆14C 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 ∆14C, salinity, and the Bakun index, suggesting that the ∆14C record is an indicator of upwelling in the Southern California Bight.