• Water Column Profiles of Dissolved Inorganic Radiocarbon for the Kuroshio Region, Offshore of the Southern Japanese Coast

      Tsuboi, Tatsuya; Iwata, Hiroshi; Wada, Hideki; Matsuzaki, Hiroyuki; Sohrin, Rumi; Hiroe, Yutaka; Ichikawa, Tadafumi; Hidaka, Kiyotaka; Watanabe, Tomoo (Department of Geosciences, The University of Arizona, 2011-12-16)
      We present the water column profiles (surface to 2000 m depth) for dissolved inorganic radiocarbon ([delta]14CDIC) from 2 stations in the Kuroshio region including the Kuroshio large meander (LM) of 2004–2005. Surprisingly, the [delta]14CDIC value varied up to 125‰ in the intermediate layer, especially near 600 m depth. In addition, the [delta]14CDIC value was approximately -150‰ at 200 m depth at the northern station of Kuroshio in August 2005. This value is ~100‰ less than other [delta]14CDIC values for the same depth. In comparison, the [delta]14CDIC water column profiles for the southern station of Kuroshio and GEOSECS station 224 decrease down to 600 m depth and were similar below 600 m depth. Our results suggest that strong upwelling associated with the Kuroshio LM has a powerful influence on the [delta]14CDIC water column profiles in the study region.
    • Δ14C and δ13C of Seawater DIC as Tracers of Coastal Upwelling: A 5-Year Time Series from Southern California

      Santos, Guaciara M.; Ferguson, Julie; Acaylar, Kayla; Johnson, Kathleen R.; Griffin, Sheila; Druffel, Ellen (Department of Geosciences, The University of Arizona, 2011-12-16)
      Marine radiocarbon (14C) 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 14C, 13C, and salinity. Results from May 2005 to November 2010 show no long-term changes in 13C DIC values and no consistent variability that can be attributed to upwelling. 14C DIC values have lowered from ~34 to about ~16, an 18 decrease from the beginning of this project in 2005, and is consistent with the overall 14C depletion from the atmospheric thermonuclear bomb pulse at the end of the 1950s. 14C 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 14C 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 14C, salinity, and upwelling would be even stronger at other sites. These data represent the longest time series of 14C data from a coastal Southern California site performed to date.