이끼섬 석산호 골격의 Sr/Ca를 이용한 대한해협의 해수 표층환경복원

Abstract

Geochemical compositions of massive coral skeletons have been used as common proxies for seasonal to decadal scale climate variations in tropical/subtropical regions. Sr/Ca ratios of coral skeletons are 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 despite the areas 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 5.5-m-long drill core of a coral mound were collected from Iki Island, Japan. The top 28 cm interval of modern Favia core and 5 cm long fossil Favia (2820 years BP) were analyzed for Sr/Ca ratios. The Sr/Ca ratios of the modern coral revealed 42 annual cycles attained by seasonal environmental changes from 1966 to 2007. Its clear seasonality likely reflects SST variation during the studied period. Sr/Ca of 2820 years old fossil Favia also showed seasonal variations, indicating their potential for a paleo-SST proxy. The results suggest that SST at 2820 BP was lower than that of today, judging from the higher Sr/Ca maxima. Weakening of the Kuroshio at 2820 years BP likely contributed to the low SST of this region. This study enables to predict the quantitative evaluation of climate change in this region.The temperature dependence of Sr/Ca ratios was estimated -0.0388 mmol/mol/˚C, whichis significantly smaller than that of the previously obtained values from Porites corals. This might demonstrate the possibility of growth stopping of coral skeleton in winter in the Korea Strait region. The agreement of winter maxima between the fossil and modern corals also indicates the lower limit of temperature that corals can calcify.