2003/09/16 第051回 - David L. Dettman 博士

第51回汽水域懇談会

9月30日(火曜日)夕方より第51回汽水域懇談会を行います。皆様お誘い合わせの上、 ご参加下さいますようお願い申し上げます。

 

『The use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual Colorado River discharge』

話題提供:Dr. David Dettman 島根大学汽水域研究センター客員教授

アリゾナ大学地球科学学部研究員のデットマン博士は、この7月に客員教授として 島根大学汽水域研究センターに赴任して来られました。安定同位体の解析などを手 法とした地球化学や古環境学、古生態学がご専門です。

 

日時:9月30日(火曜日)午後5時より1時間程度
場所:島根大学汽水域研究センター2階演習室(201)

安定同位体の解析などによって古環境や古生態系などをどのように解明していくの か、この分野の最先端を行く研究者から興味深いお話が聞けるものと思います。 皆様のご来聴をお待ちしております。


51th ReCCLE Seminar

This talk describes a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river-water / seawater mixing zone of the Colorado River estuary. Sclerochronological techniques are used to identify tidally- induced, fortnight-scale bundles of daily growth increments within shell cross-sections. These fortnightly markers are used to establish a chronology for samples taken for δ18O analysis. A composite seasonalδ18O profile derived from five shells that grew in the absence of river-water flow is used as a baseline against which profiles of river-influenced shells are compared. Because this comparison is between matched fortnights within a year, the temperature of shell growth is likely to be very similar. The difference inδ18O between the river-influenced shell and the "no-flow" composite shell therefore represents the change in theδ 18O of the water due to the presence of river water in the mixing zone. The river water end-member is also determined within a fortnightly context so that the change in theδ18O of mixing-zone water can be used to calculate the relative proportions of seawater and fresh-water. The fresh- water end-member is calculated from theδ18O of bivalves alive prior to the emplacement of dams and water diversions on the Colorado River. The marine end-member is based on direct measurements of theδ18O of northern Gulf of California water during times of no Colorado River flow. The system has been calibrated to absolute flow amounts using recent releases of known volume and rate.