• Marine Reservoir Correction for the Cocos (Keeling) Islands, Indian Ocean

      Hua, Quan; Woodroffe, Colin D.; Barbetti, Mike; Smithers, Scott G.; Zoppi, Ugo; Fink, David (Department of Geosciences, The University of Arizona, 2004-01-01)
      Known-age corals from the Cocos (Keeling) Islands, Indian Ocean, have been analyzed by accelerator mass spectrometry (AMS) for radiocarbon to determine marine reservoir age corrections. The R value for the Cocos (Keeling) Islands is 66 +/12 yr based on the analyses undertaken for this study. When our AMS and previously published dates for Cocos are averaged, they yield a R of 64 +/15 yr. This is a significant revision of an earlier estimate of the R value for the Cocos (Keeling) Islands of 186 +/66 yr (Toggweiler et al. 1991). The (revised) lower Delta-R for the Cocos (Keeling) Islands is consistent with GEOSECS 14C data for the Indian Ocean, and previously published bomb 14C data for the Red Sea, Gulf of Aden, and Cocos Islands. The revised Delta-R is also close to values for the eastern Indian Ocean and adjacent seas. These suggest surface waters that reach the Cocos Islands might be partly derived from the far western Pacific, via the Indonesian throughflow, and might not be influenced by the southeast flow from the Arabian Sea.
    • Radiocarbon in Annual Tree Rings from Thailand During the Pre-Bomb Period, AD 1938-1954

      Hua, Quan; Barbetti, Mike; Zoppi, Ugo (Department of Geosciences, The University of Arizona, 2004-01-01)
      Annual tree rings from Thailand were analyzed by radiocarbon AMS for AD 1938-1954. The results showed no significant depletion in atmospheric 14C over Thailand during the pre-bomb period, even though the air mass to Thailand during the growing season of tree rings is transported over a potentially significant source of oceanic 14C-depleted CO2, out-gassing in the northern Indian Ocean. When compared with Washington and Chile for different periods from the 17th century to AD 1954, Thailand appears to have the characteristics of Southern Hemisphere 14C. This supports our previous finding that Thailand was strongly influenced by the entrainment of Southern Hemisphere air parcels in the southwest Asian monsoon (Hua et al. 2004). For Thailand, this effect is much stronger than the reduction of atmospheric 14C in association with CO2 out-gassing in the northern Indian Ocean.