抄録
Large consumption of fossil fuels has marked the 20th century, resulting in significant introduction of CO2 into the atmosphere with its concentration increasing from a pre-industrial value of about 280 ppm in the 18th century to about 380 ppm at present and predicted further increase. Global warming related to excess emission of carbon dioxide is a burning issue for the world's environment nowadays. In turn, carbonate sediments are common and abundant in earth's surface environments. Carbonate rocks such as limestone and dolomite are a sink for extremely large amounts of carbon compared with atmospheric carbon dioxide. The mass fluxes between the atmosphere and oceans are partly controlled by reactions between carbonate minerals and natural waters. Therefore, it is potentially important to study carbonate geochemistry for understanding global and local environmental issues. The pioneer work on carbonate geochemistry in Japan was first performed by Minami and Honda at the University of Tokyo in 1942. They reported Sr/Ca in carbonate sediments and discussed the aquatic geochemical cycle of Sr-Ca (Minami and Honda, 1950). They also pointed out that Sr and Ca occur together in marine carbonates such as coral and provided a Sr/Ca value of 1.0 % (atom ratio) which is recognized as a very precise value even now. Under their great insight, they succeeded in estimating the Sr contents of stalactites and stalagmites to be 〜0.001% (w/w), even though they had no methods which could analyze Sr at such low contents (Marvin, 2003). The pioneer work by Minami and Honda might encourage Japanese carbonate geochemists to start their studies on polymorph of carbonates and the distribution of trace elements about 50 years ago. Over half a century has passed since the pioneer work. The latest technical developments of sophisticated equipment such as ICP-AES, ICP-MS, TIMS and SIMS make it possible to determine ultra-trace amounts of target elements or compounds and precise isotope ratios and also provide significant information on the palaeo environment in which the carbonate mineral was formed. In this issue, recent studies on carbonate geochemistry were compiled as a memory of the annual meeting of the Geochemical Society of Japan, held at University of the Ryukyus in September 2005. Among 22 subjects presented as oral (15) and poster (7) in the special session of carbonate geochemistry, eight selected papers are presented here. We hope these papers could help for better understanding of carbonate geochemistry associated with environmental changes.
