Vol.5 No.2 2012

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Research paper : Paleoclimate reconstruction and future forecast based on coral skeletal climatology (A. Suzuki)−83−Synthesiology - English edition Vol.5 No.2 (2012) This result refutes the possibility of the permanent El Niño theory that states that El Niño will not occur in global warming which has been the major way of thinking. Also, it strongly indicates that El Niño will continue to persist on the warmed earth. This result will provide new hints to predict El Niño and its effects in the future global warming. 5 Coral bleaching phenomenon and decreased biological diversity of coral reef caused by abnormally high seawater temperaturesThe coral bleaching phenomenon that occurred in the Great Barrier Reef of Australia in the southern hemisphere at the beginning of 1998 shifted to the northern hemisphere with the passage of seasons, and coral bleaching at a scale unseen before occurred in the coral reefs around the Ryukyu Islands in August 1998.[11] Although the biological and biochemical researches for coral bleaching were done actively particularly on the relationship between the coral and symbiotic algae, here, the focus will be on the coral skeletons. When the corals are bleached, what records are left in the skeletons?In the coral reef off the coast of Yasurazaki in the east coast of Ishigaki Island, there is a massive colony consisting of three fused Porites colonies. It was observed that during the large-scale bleaching event in 1998, bleaching was seen in one colony while bleaching did not occur in the adjacent two colonies.[12] A jump that corresponded to the bleaching period was observed in the oxygen isotope ratio profile analyzed at high resolution along the growth axis of the skeleton, and this was interpreted as the halt of coral skeleton growth for a few months immediately after bleaching.[13] Columnar samples were collected again from these colonies in September 2002, four years after the large-scale bleaching event, and x-ray images were taken for observation. It can be seen that the growth speed significantly declined in the skeletons during 1998 only (Fig. 10). As the global warming progresses and high seawater temperatures occur frequently, the growth of coral skeletons is inhibited and the environment may become unsuitable for growth. On the other hand, if the high seawater temperature condition is resolved in a short time, some of the corals such as the Porites can recover from bleaching and may be able to survive. The evaluation of the effect of abnormally high temperatures on the coral and the coral reef ecosystem is an important research topic.6 Effect of marine acidification phenomenon on the coral reefMarine acidification is recently gaining attention as a new global environmental issue.[14] The carbon dioxide released into the atmosphere by human activity migrates into the ocean to reduce the pH of seawater and the saturation of carbonates, and negatively affects the development of marine organisms and calcification of coral and foraminifers.[15][16] It is reported that in the skeletal analysis of the 328 colonies of Porites collected in 69 marine regions of the Great Barrier Reef, the calcification rate that had been stable for the past 400 years rapidly changed and decreased 14 % after 1990, and the relationship with marine acidification was indicated.[17] The boron isotope ratio (ratio of 11B and 10B) in the coral skeleton is an excellent index of seawater pH,[18] and the reconstruction of the changes in past seawater pH using the long-length coral samples and fossil corals is an important future topic of research. The analysis of boron isotope ratio is measured using the thermal ionization mass spectrometry (TIMS) or the multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and the introduction of such high-performance Fig. 11 Basic methodology of the coral skeletal climatology (lower left) and the development of three researches addressed in the paperThe meaning and interpretation of the indices used and the scenario of contribution to the final goal are presented for the three studies addressed in the paper, “Near past climate change of Ishigaki and Ogasawara reconstructed from coral skeleton,” “Reconstruction of El Niño by fossil corals from the Pliocene Warm Period,” and “Coral bleaching by abnormally high temperature.”El Niño as a universal phenomenon during the warm periodOxygen isotope ratio … El Niño index(Basic methodology) Changes in the climate system around JapanGrowth inhibition during abnormally high temperatureCoral record of Pliocene Warm Period (3.5 million years ago)Clarification of phenomenon, paleoclimate reconstructionClimatological index development (analysis + verification)Sample collectionOxygen isotope ratio … temperature index (growth index)Clarification of climate change during the warm period due to natural causesRecent abnormally high temperature and coral bleachingReconstruction of artificial global warming process after the Industrial RevolutionOxygen isotope ratio … temperature, salinitySr/Ca ratio… temperature→Dual proxy methodSkeletal record of coral beaching in 1998Coral records of Ryukyu and Ogasawara in the 19-20th centuryAdvancement of global environmental prediction (Air and seawater temperature, rainfall, coral reef and marine ecosystem)Geophysics, geologyClimatology, paleooceanographyICP element analysisCarbonate inorganic chemistryBiology, paleontologyAnalytical chemistry, geochemistryGeologyBiology, molecular biology (Integration and application of methods) (Background, elemental technology)Investigation by culture experimentSample exploration, geological survey◯Increased precision and advancement of micro-sampling method (increased temporal resolution)◯Diversification of subject element and isotopes (diversification of environmental indices)◯Increased high precision and analysis speed for element and isotope ratio◯Advancement in data analysis◯Understanding the properties of coral record (understand the quirks and use them wisely)Coral skeletal climatologyTsunami, typhoonDisaster prevention・Abnormally high temperature and mass coral bleaching・Ocean acidification and decreased calcificationDiagnosis of coral reef and marine environment(Outcome)・Increased temperature, change in rainfall・Variation in East Asian monsoons・Variation in El NiñoGlobal warming predictionOxygen and carbon isotope ratio analysisIsotope geochemistryCoral skeletonFig. 12 Scheme of research development for coral skeletal climatologyThis scheme shows the elemental technologies of the research, the basic fields, the integration of the methods that compose the body of the coral skeletal climatology and its application to the actual subject, and the social demands to which the outcome may contribute.

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