In this study, the settling particulates
collected by time-series sediment traps, sediment
cores, and seawater samples taken in the western
South Okinawa Trough were analyzed for 210Pb and
210Po in order to understand the characteristics
of the particulates and sediments based on the
distribution of these two nuclides and the extent
of their radioactive disequilibrium.
Two sediment traps were deployed at T18 (24¢X45'N 122¢X18'E, about 300m and 100m above bottom)
from February to August 1999. The results show
that higher mass fluxes were observed from
February to April, ranging between 16 and 56
g/m2/d. The 210Pb activity increases
systematically with time from about 80 to 100
dpm/g, and the upper trap has slightly higher
values. Similar to 210Pb, the 210Po activity
also increases, but from near zero to only 27
dpm/g for both traps, much lower than the
corresponding 210Pb activity.
The 210Pb activities are quite different
between the settling particulates collected by
traps at T18 and the surface sediment taken
nearby (the former have a mean activity of about
85 to 90 dpm/g; the latter has a value of only 11
dpm/g). The size distribution and elemental
composition are also different between the
trapped particulates and the sediment. Thus the
underlying sediments were not directly derived
from the overlying trapped particulates. Except
for T4 core below 15cm and T19 entire core, the
210Po/210Pb activity ratio in the sediments
varies greatly, from near zero to 0.7, indicating
deficiency of 210Po. Both 210Po and 210Pb
activities are much lower in the sediments than
in the settling particulates. A T19 both 210Po
and 210Pb activities in the core decrease steeply
from 120 dpm/g at surface to 60 dpm/g at 4 cm,
indicating radioactive equilibrium. This is
entirely different from the cores taken at other
stations.
The total 210Po/210Pb activity ratio in the
water column at T17 is nearly constant at about
0.6, but drops to 0.3 below 700m, i.e. 210Po
activity is deficient in the entire water
column. At T18, the activity ratio is about 1.3
between 100m and 300m, indicating a 210Po excess
in this layer. Below 400m, the ratio is about
0.6 to 0.7, showing 210Po deficit again. These
observations indicate that the water columns at
T17 and T18 are stratified, probably due to
lateral transport. Based on the 210Po/210Pb
activity ratio the mean residence time of 210Po
with respect to particulate scavenging ranges
from 3 to 16 months.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0719101-103520 |
| Date | 19 July 2001 |
| Creators | Chu, Kevin |
| Contributors | S. Lin, Y. C, Chung, 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-0719101-103520 |
| Rights | unrestricted, Copyright information available at source archive |
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