Radiocarbon in annual tree rings from Thailand during the pre-bomb period, AD 1938-1954

Annual tree rings from Thailand were analyzed by radiocarbon AMS for AD 1938-1954. The results showed no significant depletion in atmospheric C-14 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 C-14-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 C-14. 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 C-14 in association with CO2 out-gassing in the northern Indian Ocean.