第162回汽水域懇談会 -デイビッド デットマン 博士-【02/24開催】

公開日 2023年02月06日

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 第162回の懇談会はデイビッド デットマン 博士(アリゾナ大学/エスチュアリー研究センター客員研究員)の話題提供でハイブリット形式により行います。皆様のご参加をお待ちしております。
 第162回汽水域懇談会(日程のポスター)


第162回汽水域懇談会

題目 : Laser absorption measurement of carbonate clumped isotope ratios, a new tool for paleotemperature measurement in aquatic and terrestrial systems.
   (レーザー吸収法による炭酸凝集同位体比の測定:水域・陸域における古水温測定のための新たな手法)
話題提供者 : デイビッド デットマン 博士 (アリゾナ大学/エスチュアリー研究センター客員研究員)
日時:2023年 2月24日(金)17:00–18:30
場所: ハイブリッド開催(センター2階セミナー室(201号室)とZoom を併用)
   16:30からZoomを開設
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【講演概要】
Clumped isotope ratios in carbonates are a powerful paleothermometer, and the use of this measurement is increasing in geology and paleoclimate work. However, the analysis tends to be time consuming and expensive when measured with traditional isotope ratio mass spectrometry (IRMS). By turning to laser absorption techniques, the high precision analysis of isotope ratios of many different isotopologues of carbon dioxide can be performed quickly and without the problem of common mass interferences that are seen in IRMS measurements. I will describe a fully automated Tunable Infrared Laser instrument that extracts CO2 from carbonate samples, cryogenically removes water and non-condensables, and then measures the four isotope species of CO2 that are required for a clumped isotope measurement (16O12C16O, 16O13C16O, 16O12C18O, and 16O13C18O). This system achieves precision equivalent to high quality IRMS data (0.01‰, 1 S.E.), and it surpasses typical IRMS measurements in several features: rapid measurement (50 minutes per carbonate sample); small sample size (<20 μmol of CO2, or <2 mg equivalent calcite); and no need for an assumed 17O abundance in the sample to correct for common-mass interference. An empirical calibration, using synthetic calcites grown or equilibrated across a temperature range of 6°C to 1100°C is consistent with other published calibrations.
The advantages and limitations of clumped isotope thermometry will be discussed based on preliminary data from current research projects. Regional fluvial temperatures and the oxygen isotope ratio of local rainfall can be reconstructed using modern unionid bivalve shells from across North America. A pilot study of Lake Turkana bivalves reveals information about seasonal runoff and temperature in a river delta as well as a possible way to study the thermal structure of shallow water in this lake. Finally, seasonal variation in local relative humidity is investigated using sequential samples in a pair of land snail (Achatina) shells using both clumped and conventional (18O/16O) isotope ratios.

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