[B-PT04] バイオミネラリゼーションと環境指標

[BPT04-P04] Variation of geochemical tracers in coral skeletons (Acropora digitifera vs Porites australiensis) based on the temperature controlled culture experiment

阪田 祥子¹、*井上 麻夕里¹、田中 泰章⁵、中村 崇³、酒井 一彦²、池原 実⁴、鈴木 淳⁶ (1.岡山大学大学院自然科学研究科、2.琉球大学熱帯生物圏研究センター、3.琉球大学理学部、4.高知大学海洋コア総合研究センター、5.ブルネイ大学理学部、6.産業技術総合研究所地質情報研究部門)

キーワード：環境指標、サンゴ骨格、温度

While biogenic carbonates such as foraminifera and coccolithophorid are attractive tools to reconstruct the past environments, scleractinian corals also provide environmental data around tropical to subtropical region with much higher time resolution. For example, oxygen isotope ratio (δ¹⁸O) and strontium-calcium (Sr/Ca) ratio have been used for reconstructing sea surface temperature and salinity by generally using massive Porites sp. However, reconstructions of paleoenvironments using only Porites are sometime limited to Indo-Pacific region and specific time windows. Therefore in this study, we focus on Acropora digitifera, in addition to Porites, which dwell even in the Caribbean Sea in addition to Indo-Pacific ocean and are often found as fossil corals. We compare chemical components contained in A. digitifera and P. australiensis based on temperature controlled culture experiments in which three colonies of both corals were used. As a result, A. digitifera showed a strong negative correlation between the mean δ¹⁸O and water temperature (R²= 1.0), and the temperature dependency was comparable with that of Porites sp. Thus δ¹⁸O of A. digitifera was suggested to be useful as a temperature proxy although they were also slightly influenced by skeletal growth rate. A negative strong correlation was also observed between mean Sr/Ca ratio and temperature in A. digitifera and P. australiensis (R²= 1.0 and 0.93, respectively) without clear effects from skeletal growth rate. Therefore, it was suggested that skeletal Sr/Ca ratio in coral was predominantly controlled by water temperature although large deviations of Sr/Ca in A. digitifera even at same temperature settings were found. This deviation would be improved by subsampling along an appropriate skeletal structure composed of single polyp.