HR: 0830h
AN: OS11A-04    [Abstracts]
TI: 228Ra and 226Ra Profiles from the Northern South China Sea
AU: * Lin, H
EM: ycchung@mail.nsysu.edu.tw
AF: Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan
AU: Chung, Y
EM: ycchung@mail.nsysu.edu.tw
AF: Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan
AU: Lin, C
EM: ycchung@mail.nsysu.edu.tw
AF: Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan
AB: We previously reported the distributions of 228Ra and 226Ra in the northern South China Sea (SCS) which showed that both nuclides in surface waters were much higher than those in the open oceans because the SCS was enclosed mostly by landmasses which are known as sources of these nuclides. Large temporal and spectial variations were also observed probably due to the monsoons and intrusion of the Kuroshio Current. During a recent cruise conducted in the northern SCS in February, 2004, three vertical 228Ra profiles were measured by gamma spectrometry on the Ra isotopes which were concentrated first by the MnO2-impregnated acrylic fiber and then acid-washed as sample solution for counting. The two deep water 228Ra profiles are remarkably similar, showing high values in the surface layer and fairly uniform at about 10 to 13 dpm/100L below 200m depth but with a clear increase toward the bottom due to input from the underlying sediments. The shallow water profile on the shelf shows higher 228Ra values due to both vertical and horizontal mixing of the shelf water with additional source from the shore zone. Additional 228Ra profiles measured on samples from earlier cruises show that the deep water values may differ significantly (up to 5 dpm/100L) at the same location in different seasons or cruises. The associated 226Ra profiles are also variable but quite comparable to those in the northwest Pacific in deep water. 226Ra activities in the shallow water (less than 1000m depth) are higher in the SCS than in the open oceans. The 228Ra/226Ra activity ratios vary mostly from about 0.3 to 0.5 in the deep water. These values are much higher than those in the open oceans which are generally less than 0.1.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4835 Inorganic marine chemistry
DE: 4850 Organic marine chemistry
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly