The geochemical fingerprint of biogenic calcite is largely governed by the physical environment and water chemistry at the place and time of calcification, which is in turn related to both the ecology and phenology of the target study species. We present data on the valve chemistry (δ18O, δ13C, Mg/Ca, Sr/Ca) of living Limnocythere inopinata, a common and eurytopic Holarctic ostracode species, and on simultaneously collected water chemistry data from 15 water bodies in western Mongolia. These selected lake and pond study sites provide a fair representation of the regional trend in solute evolution towards pronounced calcium depletion, which is further characterized by good correlation between Mg/Cawater and total dissolved solids. Ostracode valve chemistry analysis showed that the Sr/Ca ratio (Sr/Cavalve) correlates better with Sr/Cawater than Mg/Cavalve does with Mg/Cawater, perhaps because Sr/Ca is less affected by calcification rate and temperature. The difference in δ18O between the collected valves and a hypothetical ostracode calcite formed during mid-summer reveals an overall coherent trend of evaporative enrichment during summer in the sampled perennial water bodies, whereas smaller and/or ephemeral water bodies appear to be stronger impacted by stochastic rain events. Among-lake variation in δ13C likely reflects the regional gradient in aquatic productivity, and the uniform pattern of relatively small mean offset between the δ13C of ostracode valves and of surface-water dissolved inorganic carbon suggests epibenthic molting behavior in a well-mixed littoral habitat. The observed patterns in water and valve chemistry further suggest that females of L. inopinata, in this particular climatic setting, molt to adult in early summer. This information on calcification time and environment contributes to more rigorous paleo-environmental interpretation of lake-sediment records of this common species in central Asia. Our results also suggest potential for quantitative salinity reconstruction based on ostracode Mg/Cavalve in western Mongolian lakes, however this needs to be constrained by insight in the local hydrology and hydrochemistry of the reconstruction site.
Bibliographical noteFunding Information:
Y. Khand and S.N. Soninkhishig provided invaluable support during fieldwork. We also thank M. Solheid who offered training and technical assistance in the University of Minnesota Isotope Laboratory. R. Knurr (Department of Geology and Geophysics, University of Minnesota) performed cation analyses on valve residues. Collection of the study material was supported by the National Science Foundation (NSF) under grants DEB-0316503 to M. Edlund and J.E.A. (Science Museum of Minnesota). This research was funded by a PhD grant of the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) to the first author. This is Contribution 11–01 of the Limnological Research Center.
Copyright 2011 Elsevier B.V., All rights reserved.
- Central Asia
- Non-marine ostracodes
- Quantitative inference
- Solute evolution
- Stable isotopes
- Valve chemistry