1. E-mail: carmohd@ukm.my
Sediment Sedimentation rate values in the Manila Bay and Thailand Gulf using 210Pb method
Che Abd Rahim Mohamed Marine Ecosystem Research Centre (EKOMAR) Faculty of Science & Technology Universiti Kebangsaan Malaysia Bangi, Selangor Malaysia

2. Topics Introduction Chronology Sampling & Analytical procedure
Results & Discussion
Major Past, Current & Future Research Plans

3. Introduction
Why Date Marine Sediments? Usually dated with two goals in mind:
(1) to establish the timing of past environmental change, and
(2) to determine the accumulation of materials (e.g. sediment, pollutants, micro-fossils) in the reservoirs.

4. Radioactive classified into two group as;
1. Natural – cosmogenic and primodial
cosmogenic – 26Al, 10Be, 7Be, etc
primodial – 238U series, 232Th series
2. Artificial or man-made – 137Cs, 241Am

5. The natural Uranium-Thorium decay series
                                                                                                                                                                                                                                                       
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6. Summary of U-Th decay series dating methods
Half-life
Dating range
Application
230Thexcess
75,200 yr
< 300,000 yr
Deep sea sedimentation rates, Mn nodule formation rate
231Paexcess
34,300 yr
< 150,000 yr
226Ra
1,602 yr
10,000 yr
Marine and terrestrial
210Pbexcess
22.3 yr
100 yr
Sedimentation rate in lakes, estuaries and coastal marine environment
228Thexcess
1.913 yr
10 yr
Rapid sedimentation rates in shallow waters
234Thexcess
24.1 days
100 days

7. Why using short half-life radionuclide?
Deposition of sediment at the coastal water, lake and estuary areas was controlled by;
a. bioturbation
b. tidal cycles
c. bottom currents
d. human activity
e. suspended solid input

8. Why using 210Pb methods? Lead-210 Chronology
- Studies for human impacts (e.g. pollution, eutrophication, erosion), which typically focus on the last years, the dating method of choice is 210Pb.
Lead-210 is a naturally occurring radioisotope in the 238U-decay series formed by decay of 226Ra, and the subsequent evasion of the intermediary 222Rn (an inert gas) from the earth's surface.
Radon-222 decays through a series of short-lived daughters to 210Pb which is stripped from the atmosphere in precipitation and accumulates in lake sediments and wetlands where it decays away with a half-life of 22 years.
Cores are typically dated by analyzing a series of stratigraphic levels from the core surface to a depth where unsupported 210Pb is no longer measurable (roughly 5-8 half-lives).
From the resulting 210Pb profile, dates are calculated according one of several mathematical models that make assumptions regarding the accumulation of 210Pb and sediment at the core site.

9. The model assumed that;
a. the flux of excess nuclides to the sediment-water interface is constant
b. the sedimentation rate is constant at all times.
c. there is no post-depositional migration of the radionuclide within the sediments.
d. the activity of daughter supported by parents in the sediments is independent with depth.

10. Calculation
Sedimentation rate from vertical profile of excess nuclide in core can be calculated from the relation;
Az = Aoe(-t)
where,
Az is the activity of excess study nuclide (dpm/g) in the sediment at any depth Z (cm) from the sediment-water interface
Ao is the activity of excess study nuclide (dpm/g) in the freshly deposited at depth Z = 0 (sediment-water interface)
t is time (year) or t = Z/S
S is the sedimentation rate (cm/yr)
210Pb is decay constant/half-life or /yr
Az = Aoe(-)(Z/S)

12. Analytical procedure
Generally, analytical procedure for uranium-thorium nuclides in sediments, suspended solid (TSS), seawater, freshwater and organisms are combination with acidification, precipitation, purification and electrodeposition.
The analytical methods using anion or cation are well established [i.e, Koide & Bruland, 1975; McCabe et al., 1979; Harada & Tsunogai, 1985; Mohamed et al., 1996 & etc.,].

13. Teflon beaker

14. 1~2 g dried sediment samples (< 125 um)
Sediment Sample Analysis
1~2 g dried sediment samples (< 125 um)
Digestion with HNO3 + HCLO4 + H2O2
Spike with Pb and Ba carrier solution
Digest 2 hours
Filter with 0.45 um
Sample solution
Heating on the hotplate
Dryness
Dissolved with 50 ml of 1% HCLO4 +
CATION COLUMN

15. Main Column

16. CATION COLUMN

18. Gross Alpha-Beta Spectrometry

19. Alpha Spectrometry

20. Gamma Spectrometry

21. RESULTS Thailand Gulf at GT 15 0.01 0.10 1.00 10.00 10 20 30 40 50 6010 20 30 40 50 60
Depth (cm)
210Pbexcess (dpm/g)
RESULTS
Thailand Gulf at GT 15

22. S = 0.66 cm/yr

23. Manila Bay
S = cm/yr

24. S = cm/yr

25. Sedimentation rate (cm/yr)
Sedimentation rate values in the various coastal regions.
Country
Name
Location
Sedimentation rate (cm/yr)
References
Malaysia
Southern South China Sea
Kelantan, Terenggau
0.10 – 0.38
This study
Malacca Straits
Kedah, Selangor
Sabah Coast
Sipitang
0.03
Tee et al (2004)
Thailand
Eastern coast Thailand Gulf
13o18.23`N;
100o 54.82`E
0.21
Srisuksawad and Rungsupa (2002)
Sichang-Sriracha
13o 7.30`N;
100o 51.7`E
Station GT 15
13o 21.52`N;
100o 34.36`E
0.66
Philippines
Manila Bay
14o 30.58`N;
120o 44.92`E
MB 14
MB 18
0.91
0.835
0.721
Sombrito et al (2002)
Vietnam
Cam Ranh Bay
Ba Ngoi
1.17
Vu Nhu Ngoc et al (2002)
Indonesia
Jakarta Bay ?
Samples in progress

26. Major Past, Current & Future Research Plans
Setup Marine Ecosystem Research Centre for conducting research in various field such science & non-science.
Current
Transboundary research in various elements
Future
South China Sea cruise on July 2008
National & International research on marine radiochemistry

27. thanks
POME Family at Jakarta 2007