Environmental Significance of the Boron Isotopic Composition in Coral Skeletons

• Main Authors: Bo-Shian Wang, 王博賢
• Other Authors: Chen-Feng You
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/84191299661479025276

碩士 === 國立成功大學 === 地球科學系碩博士班 === 93 === 　Carbon dioxide is one of the most important greenhouse gases tightly linking to the global climatic variation. Geochemical investigations have demonstrated that boron isotope in marine carbonates is the only validated record to understand pH or pCO2 of seawater in the past. In this study, coral skeleton collected from an offshore islet, Lutao, southeastern Taiwan, was used for high precision trace element and stable isotope (C, O and B) analyses. We modified the micro-sublimation technique for boron separation and purification, which was manifested not only to avoid the complicated resin procedures but also to eliminate most of the organic matter and salt interferences. A modified Cs2BO2+ TIMS technique was developed for boron isotopic analyses with precision of 0.09‰ and 0.19‰ for NBS951 (11B/10B = 4.0519, 2σm = ± 0.09‰，n = 33) and a coral standard (11B/10B = 4.1517, 2σm = ± 0.19‰, n = 7) respectively and applied successfully for 30 coral determination. The δ11B in Lutao coral skeleton varies largely from 21.3 to 29.1‰ during 1988 to 1990 (from pH = 7.6 to 8.3) with a mean value of 24.0‰. These results display strong seasonal variability, which is similar to the variation of carbon isotope and monthly average temperature. Interestingly, the variation of oxygen isotope is much smaller and shows no effect of seasonality. The boron isotopic composition of Lutao coral skeletons are affected mainly by: (1) variation of seawater pCO2 as a result of seasonal influence by intrusion of the Kuroshio Current or local upwelling; (2) short-term climatic event such as El Niño or La Niña; and (3) biological vital effect. The carbon isotopes reflect possible effects of symbiotic photosynthetic activity and the oxygen is mainly influenced both by temperature or kinetic. Future study will focus on laboratory culture experiments to evaluate possible vital artifact in coral skeleton.