Geochemistry of ostracode calcite: Part 2. The effects of water chemistry and seasonal temperature variation on Candona rawsoni

J. Xia, D. R. Engstrom, Emi Ito

Research output: Contribution to journalArticle

99 Scopus citations

Abstract

Reconstruction of lake paleochemistry from the isotope and trace-element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonally of shell formation. Monthly field collections of live Candona rawsoni from two hyposaline lakes in the eastern Dakotas reveal large variations in δ18O values (2-5‰) and Mg/Ca and Sr/Ca ratios (up to 35%) among individual adults within the same assemblage. Because the measured variations in water chemistry were small, the amplitude of ostracode δ18O and Mg/Ca variations must result from seasonal temperature variation. Ostracode Sr/Ca ratios, which should be temperature independent, shows strong positive covariance with shell Mg/Ca. These results imply that Sr uptake in ostracode calcite increases with the Mg content of the shell. The partitioning coefficient for Mg, on the other hand, appears to decreases at high values of Mg/Ca in the host water. The geochemical variability in the field collections indicates that C. rawsoni populations are composed of multiple overlapping generations that attain maturity at different times. Many juveniles apparently undergo several molts in mid-summer and persist as penultimate instars (A-1) into the following spring. Geochemical analysis of late-instar juvenile C. rawsoni from lacustrine sedimentary records is likely to provide information on mid-summer conditions. Large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate-region lakes.

Original languageEnglish (US)
Pages (from-to)383-391
Number of pages9
JournalGeochimica et Cosmochimica Acta
Volume61
Issue number2
DOIs
StatePublished - Jan 1997

Fingerprint Dive into the research topics of 'Geochemistry of ostracode calcite: Part 2. The effects of water chemistry and seasonal temperature variation on Candona rawsoni'. Together they form a unique fingerprint.

  • Cite this