骨格の酸素・炭素同位体比にみるサンゴ白化現象の記録(<特集>サンゴ年輪と低緯度の海洋環境)

概要

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Frequent coral bleaching has been observed in tropical and subtropical seas during the last three decades. These recurrent coral bleaching events may be a response to global warming. The influence of bleaching on the isotopic composition of coral skeletons has been controversial. Some studies reported clear changes associated with bleaching events, while these changes remained less evident in other reports. Since bleaching can result in a substantial decrease in skeletogenesis, a very fine sampling technique would be needed to detect the corresponding isotopic changes in the coral skeleton. We introduce a recent progress achieved by a highresolution skeletal isotope microprofiling technique. Using this technique, bleached corals from Pandora Reef, Great Barrier Reef and Ishigaki Island, Japan showed a dramatic decrease in skeletogenesis, together with a reduction in the carbon isotopic values, coincident with the worldwide severe bleaching event in 1997/98. Such changes are consistent with the hypothesis that reduced photosynthesis acts to decrease the carbon isotopic values of the skeleton. However, the drastic reduction in growth would lead to an increase in carbon isotope ratios and may have resulted in subduing the ^<13>C-response to bleaching. The results indicate that isotopic microprofiling may be the key to identifying gaps in coral growth that are diagnositic of past bleaching events.
2004-12-27