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 43600 Bangi, Selangor Malaysia 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                                                                                                                                                                                                                                                         © AWI    geochemistry   Responsible: Michiel Rutgers v. d. Loeff Webmaster Last modified: 20.2.2001

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  

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.  

Calculation Sedimentation rate from vertical profile of excess nuclide in core can be calculated from the relation; Az = Aoe(-t) ------- 1 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 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) 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

Main Column

CATION COLUMN

Gross Alpha-Beta Spectrometry

Alpha Spectrometry

Gamma Spectrometry

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

S = 0.66 cm/yr

Manila Bay S =0.721+0.002 cm/yr

S = 0.835+0.002 cm/yr

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 0.06 -0.44 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

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

thanks POME Family at Jakarta 2007