6月21日（木曜日）夕方より第80回汽水域懇談会を行います。今回はDavid L. Dettmanさんに講演をしていただきます。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。
「Geochemical partitioning of the landscape: a tool for ecology and migration studies」David L. Dettman（アリゾナ大学）
Over the last 50 years geochemists have worked to understand stable isotope variation in the landscape and the causes for the patterns that are present. This variation has a large number of causes, ranging from global cycles in elements and energy - to local temperature and hydrological variability - to nutrient and habitat partitioning in water bodies. This variability and our understanding of the underlying causes have set the stage for broad advances in the use of geochemistry in ecological studies. This talk will look at four stable isotope studies in which ecological questions and animal migration play a role. All four are based on isotopic gradients inherent in the landscape and related to significant habitat differences.
The first is a survey of bird feathers from the Matsue / Yonago region. The patterns seen in the feather chemistry reveal significant differences in food and drinking water resources for aquatic birds vs. songbirds and for local resident birds vs. long distance migrants.
Marine-terrestrial differences can also be seen in the d18O of water in an estuary. The salinity gradient in an estuary controls the distribution of habitats and the local hydro-environment that animals exploit. In the Gulf of California mixing of fresh and sea water establishes both a salinity and a d18O gradient and different d18O values are recorded by animals utilizing different salinity regions. Isotopic analysis of both shells and fish otoliths demonstrate habitat preferences and utilization.
Elevation is a major control on climate and habitat for animal communities and the study of paleoelevation has become a hot-topic in the geological community. There are a number of studies using the isotopic chemistry of mammal teeth to infer local elevation. Although the isotopic composition of tooth enamel can be related to the d18O of drinking water and food, the variation of carbon and oxygen isotopes in the landscape do not always allow the inference of paleo-elevation. A study in northwest North America seems to work well, while there are significant problems with tooth (and stable isotope) based studies of Tibetan Plateau paleoelevation.
The isotopic chemistry of large columnar cacti in the Sonoran desert reflect seasonal cycles in cool/dry and hot/wet climate. Variability in these cycles shows the balance between drought and wet years in the monsoon environment of southern Arizona. Carbon isotope ratios reflect seasonal changes in the photosynthetic strategies caused by the degree of aridity. Oxygen isotope ratios reflect the integrated evaporative loss of water through the epidermis of the Saguaro.