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: carmohd@ukm.my

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 

                                                                                                                                                                                                                                                 

     

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   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