Delta C-14 AND delta C-13 OF SEAWATER DIC AS TRACERS OF COASTAL UPWELLING: A 5-YEAR TIME SERIES FROM SOUTHERN CALIFORNIA

Marine radiocarbon (C-14) is a widely used tracer of past ocean circulation, but very few high-resolution records have been obtained. Here, we report a time series of carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from the Newport Beach pier in Orange County, within the Southern California Bight, from 2005 to 2010. Surface seawater was collected bimonthly and analyzed for Delta C-14, delta C-13, and salinity. Results from May 2005 to November 2010 show no long-term changes in delta C-13 DIC values and no consistent variability that can be attributed to upwelling. Delta C-14 DIC values have lowered from similar to 34% to about similar to 16%, an 18% decrease from the beginning of this project in 2005, and is consistent with the overall C-14 depletion from the atmospheric thermonuclear bomb pulse at the end of the 1950s. Delta C-14 DIC values, paired with salinity, do appear to be suitable indicators of upwelling strength with periods of upwelling characterized by more saline and lower DIC Delta C-14 values. However, a similar signal was not observed during the strong upwelling event of 2010. These results were obtained in the Southern California Bight where upwelling is fairly weak and there is a complex oceanographic circulation in comparison with the remaining western USA coastline. It is therefore likely that the link between DIC Delta C-14, salinity, and upwelling would be even stronger at other sites. These data represent the longest time series of Delta C-14 data from a coastal Southern California site performed to date.