Kevin C Druffel-Rodriguez

The Keck Carbon Cycle AMS laboratory, University of California, Irvine: Initial operation and a background surprise

A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported (super 14) C AMS background: charge exchange tails from (super 14) N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.

Magnesium Perchlorate as an Alternative Water Trap in AMS Graphite Sample Preparation: A Report on Sample Preparation at KCCAMS at the University of California, Irvine

We present a brief discussion of sample preparation procedures at the Keck Carbon Cycle Accelerator Mass Spectrometer (KCCAMS), University of California, Irvine, and a systematic investigation of the use of Mg(ClO (sub 4) ) (sub 2) as an absorptive water trap, replacing the standard dry ice/ethanol cold finger in graphite sample preparation. We compare high-precision AMS measurement results from oxalic acid I and USGS coal samples using Mg(ClO (sub 4) ) (sub 2) under different conditions. The results obtained were also compared with those achieved using the conventional water removal technique. Final results demonstrate that the use of Mg(ClO (sub 4) ) (sub 2) as an alternative water trap seems very convenient and reliable, provided the Mg(ClO (sub 4) ) (sub 2) is replaced frequently.

VARIABILITY OF MONTHLY RADIOCARBON DURING THE 1760s IN CORALS FROM THE GALAPAGOS ISLANDS

Radiocarbon (∆14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average ∆14C value of -62‰ is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760-1771 (±6 yr). High ∆14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low ∆14C values were obtained mid-year during strong upwelling. The average seasonal variability of ∆14C was 15-25‰, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high ∆14C values were found during 1762-1763 and 1766. A spectral analysis revealed that the spectral density for the ∆14C data displays most of its variance at the 5-yr cycle, which is reflective of El Nino periodicity during the 20th century. Corals reflect the ∆ 14 C in surface DIC and provide time histories of ∆ 14 C on timescales of months to millennia. Records of ∆ 14 C in the surface ocean reveal past variability of surface-subsurface mixing and horizontal current shifts. We report monthly ∆ 14 C measurements from a Galapagos coral representing the 11-yr period AD 1760-1771 (±6 yr). We show that ∆ 14 C is high during the beginning of the year, when trade winds and upwelling were weak, and low ∆ 14 C values during the rest of the year, when wind-driven upwelling was strong.