SEMINAR: OI Seminar Series - Tsuyoshi Watanabe

Title: High-resolution windows for marine environments and biological responses in biogenic carbonates

Abstract: Coral sclerochronology: Reef-builders of corals are present today in the tropical and sub-tropical oceans and can be found in a significant fraction of the geologic record extending back to the middle Triassic. Their skeletons continuously grow up to one of the largest biological architectures, which support various and wealth life in nutrient poor regions. Tropical corals could record long term growth histories in annual bands of their skeletons as well as marine environments during their growth periods up to several hundreds years. Other marine organisms such as molluscs and screlosponges have also daily to annul bands in their skeleton, which are useful as high-resolution chronology of the daily to century scale time windows. High-resolution reconstruction of tropical climates: The tropical oceans drive climatic phenomena such as the El Nino-southern oscillation (ENSO) and the Asian–Australian monsoon, which have global scale impacts. In order to understand climatic developments in future warming earth, it is essential to understand how the tropical climate has developed in the past, on both short and longer timescales. The geochemistry in biogenic carbonates such as 　corals, molluscs, and screlosponges has been widely used as proxies for past environmental changes in the tropical and subtropical oceans because the isotopic and elemental composition of their skeletons are believed to vary as a function of several environmental parameters (such as seawater temperature, salinity, light, nutrient). Biological responses in past and future warming earth: Experimental and model studies are suggesting that recent past and future global warming and ocean acidification due to rising atmospheric carbon dioxide concentrations would have dramatically influenced on the calcification processes of marine organisms. However, few direct evidences have existed to address how warming and acidification would play it for marine ecosystem. Geochemical and physiological data in biogenic carbonates from different time windows could be useful for future predictions of biological response in tropical oceans.