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Title :サンゴ骨格への微量元素の共沈を規定するサンゴ礁環境因子に関する研究
Title alternative :Studies on factors controlling coprecipitation of minor and trace elements in coral skeletons associated with coral reef environments
Authors :田中, 健太郎
Authors alternative :Tanaka, Kentaro
Issue Date :Mar-2011
Abstract :学位の種類(博士(理学)),学位授与機関(琉球大学),授与年月日(平成23年3月23日),学位記番号(理工研第205号)
The purpose of this study is to investigate the relationship between minor element in coral skeleton and seawater environment such as carbonate equilibrium system and heavy metal pollution. In order to elucidate the controlling factors for fluoride incorporation into coral aragonite (CaCO_3), the mole ratio of fluorine to calcium (F/Ca) in coral skeletons was analyzed by using the ion-chromatograph method. The analyzed F/Ca in coral shows a simple linear correlation with calculated seawater [F^-]^2/[CO_3^<2->]. This finding suggests that F/Ca in coral skeletons is possibly controlled by carbonate ion concentration in seawater. Such a correlation was also observed between non-symbiotic coral from Tosa Bay (water depth 185-350m), Japan and calculated [F^-]^2/[CO_3^<2->] in deep water. In order to elucidate the controlling factors for boron concentratiop in coral aragonite, the mole ratio of boron to calcium (B/Ca) in coral skeletons was determined by using prompt gamma ray analysis (PGA). Assuming the ion-exchange reaction: CaCO_3(s) +B(OH)_4^-(aq) = Ca(HBO_3)(s) + HCO_3^-(aq) for the coprecipitation process of B in coral aragonite, B/Ca is expressed as: B/Ca =K'_B [B(OH)_4^-]/[HCO_3^-], suggesting that B/Ca in coral is controlled by K'_B and seawater [B(OH)_4^-]/[HCO_3^-]. With an increase in temperature (19-29 ℃), the value of K'_B clearly shows a trend of decrease at ~50%, while seawater [B(OH)_4^-]/[HCO_3^-] increases at ~35%, indicating that temperature dependence of K'_B is larger than that of seawater [B(OH)_4^-]/[HCO_3^-]. Therefore B/Ca in coral decreases with increasing temperature. This finding suggests that B/Ca in coral is mainly controlled by K'_B which has strong temperature dependency. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique was applied for the analysis of heavy metal (V, Cd, Hg, Pb) content in Porites corals collected from Khang Khao Island between 1982-2008 in order to elucidate the anthropogenic input of heavy metals into the Gulf of Thailand. For some coral samples from Khang Khao, unsystematic variation and large peaks in metal content are observed. The average metal content in Khang Khao coral is larger than that in coral from an unpolluted reef (Rukan-sho, Okinawa). These findings indicated that the Gulf of Thailand is suffered from discontinuous inputs of anthropogenic heavy metals between 1980's to 2000's.
Type Local :学位論文
Publisher :田中健太郎
URI :http://hdl.handle.net/20.500.12000/21232
Appears in Collections:Doctoral Dissertation (Graduate School of Engineering and Science)

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