대한해협에 분포하는 석산호 골격의 Sr/Ca를 이용한 고해양의 고해상도 복원

Abstract

Geochemical composition of massive coral skeletons has been used as a common proxy for seasonal to decadal scale climate variations in tropical/subtropical regions. Sr/Ca ratio of coral skeletons is especially useful for reconstruction of past sea surface temperature (SST) since it varies depending only on SST. Favia sp. (Family Faviidae), a hermatypic massive coral, is distributed from tropical to higher latitude regions, even in the Korea Strait, located at 34N, despite the area's low SST. Thus, Favia can serve as a high-resolution paleoenvironmental archive in the East Asia marginal seas including the Korea Strait.For paleo-SST reconstruction of the Korea Strait region, a 90 cm-long core of living Favia speciosa and a 5.5 m-long drill core of coral mound were collected from Iki Island, Japan in 2007. The top 28 cm interval of modern Favia core and 5 cm long fossil Favia (2820 yr BP) were selected for the measurement of Sr/Ca and then SST reconstruction. The analytical works are still in progress. So far, the determined Sr/Ca of the modern coral revealed 21 annual cycles attributed by seasonal environmental changes from 1987 to 2007. Such a clear seasonality seems likely to reflect SST variations. The temperature dependence of Sr/Ca was estimated -0.0388 mmol/mol/C, which may demonstrate the possibility of stopping of coral skeleton growth in winter. Sr/Ca of 2800 year-old fossil Favia also showed seasonal variations, indicative of their potential for a paleo-SST proxy. SST seemed lower in 2820 yr BP judging from its higher summer maxima than the modern one. The similarity of winter maxima between Sr/Ca of the fossil and modern corals indicates the lower limit of temperature that corals can calcify. With completion of Sr/Ca measurement for modern Favia coral, it is possible to reveal SST variations of the study region for the past 41 years. This study is expected to enable to evaluate global warming in this region quantitatively.