Abstract
This thesis discusses 226Ra distribution in the seawater of the East China Sea and the sea off northeastern Taiwan. Six profiles and fifteen surface water samples were measured. Water samples were collected during cruises 493 and 523 in July, 1997 and July, 1998, respectively. 226Ra measurements were performed by the regenerated 222Rn method that had been widely used for seawater samples. The surface water 226Ra activities vary between 8.7 and 15.9 dpm/100kg in the East China Sea. There is an increase in surface water 226Ra northward toward the estuary of the Changjiang. This variation is somewhat similar to that observed in the East China Sea by Nozaki et al. (1976). The surface water 226Ra activities vary between 9.1 and 10.8 dpm/100kg in the area off northeastern Taiwan. There values are higher than KEEP-MASS cruise of July, 1992. The Kuroshio Current not easy to enter shelf, so the dilution effect of Kuroshio is smaller. Otherwise, There are 226Ra in profiles were measured from six stations on Cruise 493 (13 and 15) in Kuroshio area and Cruise 523 (5, 7, 13 and 15) in shelf. The deep water profile on Cruise 493 (st.13) displays a phenomenon 226Ra increase from about 9.7 dpm/100kg at 5m to about 14.3 dpm/100kg at 500m, station 15 from Cruise 493 displays a phenomenon 226Ra increase from about 9.8 dpm/100kg at 5m to about 17.7 dpm/100kg at 800m. 226Ra profile at station 7 showed that the gradient from 600m to 750m is large, and 226Ra concentration does not increase below this depth. 226Ra maybe associated with nepheloid layer due to lateral or horizontal transport of the water mass.
Each 226Ra profile shows a downward increase from less than 10 dpm/100kg at the surface, and shows the underlying sediments as the main source.
Based on the radioactive disequilibrium observed between 210Pb and 226Ra, all the ratios of Pb-210/Ra-226 in Station 13 are greater than 1, except at 400m. The 210Pb concentration is high and the ratio of Pb-210/Ra-226 is greater than 1 at 800m.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0914101-135829 |
| Date | 14 September 2001 |
| Creators | Chang, Terry |
| Contributors | Y. C. Chung, S. W. Lin, C. C. Chen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0914101-135829 |
| Rights | unrestricted, Copyright information available at source archive |
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