sediment sedimentation rate values in the manila bay and thailand gulf using 210pb method che abd...
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Sediment Sedimentation rate values in the Manila Bay and Thailand Gulf using 210Pb method
Che Abd Rahim MohamedMarine Ecosystem Research Centre (EKOMAR)
Faculty of Science & TechnologyUniversiti Kebangsaan Malaysia
43600 Bangi, SelangorMalaysia
E-mail: [email protected]
Topics
• Introduction• Chronology• Sampling & Analytical procedure• Results & Discussion• Major Past, Current & Future Research Plans
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.
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
The natural Uranium-Thorium decay series
© AWI
geochemistry
Responsible: Michiel Rutgers v. d. Loeff WebmasterLast modified: 20.2.2001
Summary of U-Th decay series dating methodsDating method
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
Deep sea sedimentation rates, Mn nodule formation rate
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 Rapid sedimentation rates in shallow waters
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
Why using 210Pb methods?Lead-210 Chronology- Studies for human impacts (e.g. pollution, eutrophication, erosion), which
typically focus on the last 100-200 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.
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.
CalculationSedimentation rate from vertical profile of excess nuclide in core can
be calculated from the relation;
Az = Aoe(-t) ------- 1where,
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 0.0318/yr
Az = Aoe(-)(Z/S) --------- 2
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.,].
Teflon beaker
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
Sediment Sample AnalysisSediment Sample Analysis
Main Column
CATION COLUMN
Load liquid sample into the Cation Column
Rinse Cation Column with 100 ml of 1M HCl Rinse Cation Column
with 200 ml of 2M HCl
Collect Pb solution and dry to dryness
Dissolve white paste with 50 ml of 0.5M HNO3 and continue spike 1 ml of H2SO4
PbSO4
Counting 210Pb activities using Beta counter after 1 month
Collect Radium-Barium liquid and dry to dryness
Dissolve white paste with 50 ml of 0.5M HCl
and continue spike 1 ml of H2SO4
RaBaSO4
Counting 226Ra activities using Alpha counter after 1 month
Gross Alpha-Beta Spectrometry
Alpha Spectrometry
Gamma Spectrometry
0.01
0.10
1.00
10.00
0 10 20 30 40 50 60
Depth (cm)
210Pbexcess (dpm/g)
Thailand Gulf at GT 15
RESULTS
210Pbex (dpm/g)
0.1 1 10D
epth
(cm
)
20
25
30
35 S = 0.66 cm/yr
Manila Bay
MB 18
0
20
40
60
80
100
0 10 20 30 40 50 60 70 210Pb(Bq/kg)
Dep
th (c
m)
MB 18
y = -23.267x + 106.27R2 = 0.9823
0
20
40
60
80
100
0 1 2 3 4 Ln(210Pbex)
Dep
th (c
m)
S =0.721+0.002 cm/yr
MB 14
0
20
40
60
80
100
0 5 10 15 20 25 30 35 210Pb(Bq/kg)
Dep
th (c
m)
MB 14
y = -26.934x + 97.062R2 = 0.9941
0
20
40
60
80
100
0 1 2 3 4 Ln(210Pbex)
Dep
th (c
m)
S = 0.835+0.002 cm/yr
Sedimentation rate values in the various coastal regions.
CountryName Location Sedimentation
rate (cm/yr)References
Malaysia Southern South China Sea
Kelantan, Terenggau 0.10 – 0.38 This study
Malacca Straits Kedah, Selangor 0.06 -0.44 This study
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
0.21 Srisuksawad and Rungsupa (2002)
Station GT 15 13o 21.52`N; 100o 34.36`E
0.66 This study
Philippines Manila Bay 14o 30.58`N; 120o 44.92`E MB 14MB 18
0.91
0.8350.721
Sombrito et al (2002)
This studyThis study
Vietnam Cam Ranh Bay Ba Ngoi 1.17 Vu Nhu Ngoc et al (2002)
Indonesia Jakarta Bay ? ? Samples in progress
Major Past, Current & Future Research Plans
• Past– 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
POME Family at Jakarta 2007
thanks