Time: 15:00-16:00, 19 July (Friday)
Venue: Lecture Hall 221, Institute of Surface-Earth System Science (Building No. 16)
Topic: Coral Sclerochronology: High-temporal resolution windows for palaeoclimatology, paleoceanography, and paleoecology
Speaker: Dr. Tsuyoshi Watanabe (Hokkaido University/KIKAI institute for coral reefs sciences)
Dr. Tsuyoshi Watanabe is currently a senior lecturer in the Department of Earth and Planetary Sciences, Hokkaido University. In 1999, he obtained his doctoral degree in Environmental Earth Science at Hokkaido University. During 1999-2004, he did post-doctoral research in the Geological Survey of Japan, The Australian National University, University of Tokyo, and Laboratoire de Sciences du Climat et de l'Environnement, Laboratoire Mixte CNRS-CEA. He has worked at Hokkaido University since 2004, during which he was a visiting researcher at the University of Tokyo, RWTH Aachen University and University of Hawaii. He was honored The Geochemical Society of Japan Award for Young Scientist in 2003, and the Kawaguchi Award (Japanese Coral Reef society) in 2008. Research interests of Dr. Watanabe include: 1) High-resolution climate/environmental reconstruction of palaeoenvironments using carbonates, 2) Bio mineralizarion and preservation of biogenic carbonates, and 3) Biogeochemical cycles and biological response on climate changes throughout the earth history. As first/corresponding author, he has published several papers in a series of high impact journals, such as Nature, Geology, GCA, GRL, JGR, etc.
Abstract:
The daily and annual growth bands formed in biogenic carbonates such as coral skeletons and molluscan shells could serve as the high-temporal resolution archives for the environmental and/or physiological changes during their life span. We use skeletological and geochemical approaches to investigate the histories recorded in living and fossil specimens. Understanding the past climate variability and oceanographic events in the tropical ocean is a high priority as long-term observation is very limited in these areas. Tropical shallow water corals could live up to several hundred years and the decadal to century-scale of climate and oceanic signals such as global warming, ocean acidification, El no-Southern Oscillation (ENSO), anthropogenic CO2 uptake, atmosphere, marine pollution, river discharge, and ocean circulation dynamics could be detected via reconstructing temperature, salinity, pH, nutrient, and chemical composition in seawater by using isotopic (e.g. oxygen, carbon, boron, lead, and nitrogen isotopes) and elemental (e.g. Sr/Ca, Mg/Ca, and Ba/Ca ratios) analysis along growth direction.
Ocean acidification and rising atmospheric CO2 with global warming are also predicted to severely damage the calcification processes of marine organisms and, thus, the sustainability of marine ecosystems in the near future. The skeletal density, extension rate, and calcification rate deduced from coral cores could be useful to estimate the response and acclimatization against such environmental changes during last few hundred years and to predict the future of coral reefs and ecosystems exhibiting coral acclimation to warmer, more acidified, and polluted conditions.
On the other hand, such recent advance of microanalytical techniques also revealed large heterogeneity of these isotopic and elemental composition in nano to sub-micrometer scale of skeletal microstructures, which are difficult to explain simply by surrounding environmental changes, suggesting understanding biomineralization processes in cellular level with more complexity and plasticity are important to establish more reliable proxy for past environmental changes. I would like to introduce our recent and on-going researches applied on modern and fossil specimens in the western Pacific, Indian Ocean, and the Caribbean Sea and also recent efforts to understand the biomineralization process of coral reef dweller.
References:
Yamazaki, et al. (2016) A 150-year variation of the Kuroshio transport inferred from coral nitrogen isotope signature, Paleooceanography.
Yamazaki, et al. (2014) The coral d15N record of terrestrial nitrate loading varies with river catchment land use, Coral Reefs.
Ohmori, et al. (2013) Lead concentration and isotopic composition in the Pacific sclerosponge (Acanthochaetetes wellsi) reflects environmental lead pollution, Geology.
Sano et al. (2012) Past daily light cycle recorded in the strontium/ calcium ratios of giant clam shells, Nature Communication.
Watanabe, et al. (2011) Permanent El Nino during the Pliocene warm period not supported by coral evidence, Nature, 471.
