サンゴなどの生物起源炭酸塩および鍾乳石の酸素・炭素同位体比にみる反応速度論的効果

概要

論文の詳細を見る
In this review, we examined the signal-recording ability of hermatipic corals, together with speleothem, by analyzing their fluctuations of oxygen and carbon isotope ratios (δ^<18>O and δ^<13>C) and controlling factors. Corals provide high-resolution climate and environmental records for the tropical shallow waters. The coral δ^<18>O reflects to changes in the sea surface temperature and δ^<18>O of the ambient seawater (which is related to salinity). The observed offset of the coral δ^<18>O-temperature relationship from isotope equilibrium, which is known as the "vital effect", is apparently caused by growth-rate related kinetic isotope effects. Skeletal δ^<18>O and δ^<13> showed out-of-phase annual fluctuations in shallow waters, faster-growing corals from Sekisei Reef of the Ryukyu Islands. In contrast, in deep waters, slower growing corals, δ^<18>O and δ^<13>C fluctuations were in phase, which was identified as a pattern influenced by kinetic isotope effects. A temperature-controlled tank experiment revealed that the observed large variation (〜1‰) in δ^<18>O values was attributable to growth-rate-related kinetic isotope effects. Because such large influences from kinetic isotope effects were observed in coral skeletal records, careful examination is needed for attributing these offsets to possible environmental causes. Similar story can be seen in isotopic records of speleothem, which is a unique archive of past climate on land. Calcite precipitated in disequilibrated condition may not record proper environmental signals due to strong influences of kinetic isotope effects. So-called "Hendy test" can serve as a useful tool for excluding speleothem records unsuitable for paleoclimate reconstruction.
2007-03-25

サンゴなどの生物起源炭酸塩および鍾乳石の酸素・炭素同位体比にみる反応速度論的効果

スポンサーリンク

概要

著者

関連論文

スポンサーリンク