首页

活动/通知

【聚焦关键】Past daily light cycle recorded in the Sr/Ca ratios of giant clam shells

2018-12-26 449

报告时间:2019年1月4日13:30-14:30

报告地点:天津大学卫津路校区会议楼第八会议室

主讲嘉宾:Yuji Sano (佐野有司教授日本东京大学

报告摘要:

Marine calcium carbonate such as coral skeleton and bivalve shell may record past environmental and/or ecological information as the chemical and isotopic compositions. These past information have been studied by the analyses of modern and fossil materials. Past climate reconstruction from the carbonate greatly contributes to understanding of the climate system and global warming. However, the climate change of tropical and sub-tropical region is relatively unknown due to the limited instrumental observation, luck of historical documents and insufficient dendrochronology. The aim of this study is to reconstruct the past marine environment at high resolution by the analysis of biogenic calcium carbonate using state-of-the-art microanalytical technique. The NanoSIMS is capable to analyze the solid sample surface with a high sensitivity and a high precision at sub-micron scale. Initial stage of this project comprised with the matrix-matched standard reference materials, and development of new analytical procedures at a few micro-meter. We have measured minor (Mg and Sr) and trace (Ba) elements of living giant clam and fossil clam shells. Living sample (Tridacna derasa) was cultivated from March 2002 to October 2005 at Kabira coral reef of Ishigaki Island in the southwestern part of the Ryukyu Archipelago, southern Japan. A clear seasonal variation in Sr/Ca ratio is observed in longer set of measurements with 50 micro-meter resolution. In addition, the ratio exhibits striking diurnal variations by 2 micro-meter resolution, reflecting the daily light cycle. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these annual and diurnal variations. About 5000 years old fossil sample (Tridacna gigas) was collected in August 2007 at Shiraho coast of the same island. The Sr/Ca ratios in the winter layers of the sample are characterized by a striking diurnal cycle consisting of narrow growth lines with high Sr/Ca ratios and broad growth bands with low Sr/Ca ratios. These variations, which are consistent with those of the cultivated clam shell, indicate the potential for the reconstruction of the variation in solar insolation during the middle Holocene at a few hours resolution.

嘉宾简介:

Yuji Sano is a professor of geochemistry at Atmosphere and Ocean Research Institute, the University of Tokyo in Japan. He received BS (1978), MS (1980) in chemistry, and doctorate degree (1983) in geophysics from the University of Tokyo. He studied the geochemistry of volatile element isotopes such as helium, carbon, and nitrogen in volcanic and environmental systems as a research associate in the Laboratory for Earthquake Chemistry, the University of Tokyo and as an associate professor in the Department of Earth and Planetary Science, Hiroshima University. After promotion to full Professor at Hiroshima University, he introduced a large ion microprobe (SHRIMP) and invented the method for U-Pb dating of apatite. He moved to the Atmosphere and Ocean Research Institute, the University of Tokyo in 2001 and established a noble gas laboratory for atmospheric and oceanic research and the NanoSIMS laboratory for paleoceanography and planetary sciences. He was editor-in-chief of Geochemical Journal from 2008 to 2011 and is a Fellow of the American Geophysical Union.