Controls on the stable isotope composition of seasonal growth bands in aragonitic fresh-water bivalves (unionidae) |
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| Institution: | 1. Institute of Geosciences, University of Mainz, Johann-Joachim-Becher-Weg 21, 55128 Mainz, Germany;2. Institute for Geology, Leibniz University Hanover, Callinstraße 30, 30167 Hanover, Germany;1. Illinois Natural History Survey, Illinois River Biological Station, Havana, IL 62644, USA;2. Center for Bottomland Hardwoods Research, US Forest Service, Oxford, MS 38655, USA;1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Centre for Research and Education on Biological Evolution and Environment and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210023, China;2. GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany;3. Department of Geology, Under the School of Earth, Biological and Environmental Science, Central University of South Bihar, SH 7, Gaya-Panchanpur Road, Village Karhara, Post Fatehpur, Gaya 824236, Bihar, India;4. Palaeontology Division, Geological Survey of India, Central Headquarters, 15 A & B Kyd Street, Kolkata 700016, India;5. Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 11, 24118 Kiel, Germany;6. Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany |
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| Abstract: | Water temperature, oxygen isotope composition and the δ13C of dissolved inorganic carbon were measured in 2 southern Michigan rivers, the Huron River and Fleming Creek, between late September 1990 and June 1992. The final full year of shell growth in 3 unionids collected in 1992 from these rivers was sampled for stable isotope analysis with a resolution of 30 μm. The δ18O of both shell nacre and the prismatic layer is accurately predicted by a fractionation relationship developed for biogenic aragonite. High resolution sampling of 3 species and bulk sampling of 3 other species suggest that all unionids adhere to this oxygen isotope fractionation relationship. This relationship is used to show that shell growth ceases below approximately 12°C. In these 2 settings the average δ18O value of shell (PDB scale) is within 0.5‰ of the average δ18O of river water (SMOW scale). Unionids can therefore be used in oxygen-isotope-based paleoclimatic and paleohydrologic reconstructions. In contrast, the carbon isotope ratio of shell is not accurately predicted by published fractionation factors between D.I.C. and carbonate. Shell δ13C is more negative than predicted values and the offset is highly variable suggesting a significant and variable incorporation of metabolic carbon into the shell carbonate. |
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