Vol.5 No.2 2012

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Research paper : Paleoclimate reconstruction and future forecast based on coral skeletal climatology (A. Suzuki)−84−Synthesiology - English edition Vol.5 No.2 (2012) analysis devices is essential in the advancement of research.7 Summary and future prospectIt was shown that the coral skeleton is excellent as a medium recording the past global climate changes, and that the attempts to read the record of climate change have advanced by using the state-of-the-art technology (Fig. 11). The necessity for coral skeleton research is expected to increase in the future as the global warming prediction becomes advanced. Also in the Fourth Assessment Report of the IPCC, the decrease in rainfall is predicted in the subtropical zone according to the climate model, but its accuracy must be raised.[9] The reconstruction of the past salinity oscillation that is closely related to rainfall, along with seawater temperature, is an immediate concern. This can be met by the composite index method using oxygen isotope ratio and Sr/Ca ratio as exemplified by the coral skeletons of Ogasawara. This method can be applied to fossil corals, and there is an example of investigation of coral fossils from the last ice age in the East China Sea.[19] The Fifth Assessment Report of the IPCC is scheduled for publication around 2013. Until then, it is necessary to promote the pH reconstruction by boron isotope ratio analysis and the analysis of climate change by the dual proxy method of oxygen isotope ratio and Sr/Ca ratio, and to reflect the results in the Fifth Assessment Report. Therefore, further promotion of coral skeletal climatology is needed.On the other hand, there are points that need to be clarified, such as the basic mechanism of why the climatological factors such as seawater temperature are recorded in the chemical and isotope compositions of the coral skeletons.[20] In addition to the geochemical methods, it is necessary to conduct culture experiments[21][22] and molecular biological methods[23] to clarify the biological mechanism. The researches that transcend the conventional disciplines may allow application to the prediction and evaluation of calcification inhibition of marine organisms that may be caused by the future marine acidification (Fig. 12).The 2011 off the Pacific coast of Tohoku Earthquake (Great East Japan Earthquake) occurred on March 11, 2011, and major damages occurred due to the tsunami to the Pacific coast of the Tohoku and Kanto regions. The re-evaluation of the past tsunami damages throughout Japan is an urgent issue. Particularly, the tsunamis of the Jogan Earthquake that struck the Tohoku region in 869 and of the Meiwa Earthquake that occurred in the South Ryukyu region in 1771 are gathering attention due to the similarities to the earthquake in 2011, in the height of the tsunami and the scale of casualties. The methods of coral skeletal climatology can be applied to disaster research by looking at the Porites boulders pushed ashore by the tsunami. The author’s research group applied the radiocarbon dating method and the coral skeletal climatology method to the Porites boulders scattered on the east coast of Ishigaki Island, Southern Ryukyu, and demonstrated that these were washed ashore by the Meiwa tsunami.[24][25] The contribution to the research on the Meiwa tsunami, which was a historical earthquake-caused tsunami in the Okinawa region, has high social demand from the perspective of regional disaster prevention.AcknowledgementThis paper is based on the joint researches with the people listed below. I express my sincere gratitude. Professor Hotaka Kawahata, Dr. Yusuke Yokoyama, and Dr. Mayuri Inoue of the Atmosphere and Ocean Research Institute, The University of Tokyo; Dr. M. K. Gagan, The Australian National University; Dr. T. Felis, Universität Bremen; Professor Kazuhiko Sakai, Dr. Akira Iguchi, and Dr. Akihiro Iwase of the Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus; Dr. Yukihiro Nojiri, Center for Global Environmental Research, National Institute for Environmental Studies; Professor Naotatsu Shikazono, Faculty of Science and Technology, Keio University; Professor Hironobu Kan, Okayama University; Dr. Tsuyoshi Watanabe, Hokkaido University; Kohei Hibino, General Environmental Technos Co., Ltd.; Dr. Sumiko Tsukamoto, Tokyo Metropolitan University; Dr. Masayuki Nagao, Dr. Takashi Okai, and Dr. Hitoshi Tsukamoto of AIST. I would also like to thank the following people who conducted coral skeletal research at AIST as interns: Yuriko Kashio, Takanori Sato (Tokyo Metropolitan University), Ikuko Kato (Okayama University), Dr. Tomoaki Tsunoda, Yuko Tago, Gene Taira, Hisato Izumida, Eri Takahashi (Keio University), Dr. Mari Mishima, Mamito Koizumi, Tatsuya Kobayashi, Dr. Hiroyuki Ushie, Daisuke Araoka, Yuta Kawakubo, Ayaka Fukushima, Erika Hayashi (The University of Tokyo), Dr. Tamano Omata (Japan Agency for Marine-Earth Science and Technology), and Tatsunori Kawashima (Hokkaido University).TerminologyTerm 1:Little Ice Age: the period of cold climate that occurred from about the mid 14th century to the mid 19th century. Concerning the degree of temperature decrease and regions, there is much that remains unknown.Term 2:Holocene: the most recent of the geological time divisions (epoch) and includes the present age. It covers from about 10 thousand years ago when the last ice age ended to present.Term 3:Pliocene: one of the geologic epochs of the Cenozoic Era. It covers the period from about 5 million years ago to about 2.58 million years ago. The first humans such as Australopithecines appeared during this epoch.

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