Oxygen-isotope systematics of the nektic ostracod australocypris robusta

Allan R. Chivas, Patrick De Deckker, Sue X. Wang, Joseph A. Cali

    Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

    37 Citations (Scopus)

    Abstract

    Individual specimens of the euryhaline non-marine nektic ostracod Australocypris robusta were reared from the penultimate growth stage to adulthood in controlled in-vitro experiments. Four different water temperatures (12°, 15°, 20°, 25°C), four different water salinities (15‰, 35‰, 45‰ and 65‰, each of sea-water like solute composition) encompassing 6 different water isotopic compositions (with δ18OV-SMOW varying from -13.2 to +4.3%o) were used. We measured the δ18O values of both ‘bulk’ ostracods (groups of 2 to 6 valves weighing from 95 to 225 µg/analysis), and individual, commonly poorlycalcified, valves (to as little as 12 µg CaC03), and show that 1SO/16O fractionation is independent of valve size or degree of calcification. The relationship between δ18O of the cultured valves and of the δ18O of their host waters is linear and strongly temperature-dependent. At 15-25°C, the ostracod calcite is about 0.7%o more enriched in 18O than inorganically precipitated calcite at the same temperatures. At 12°C, the 18O/16O fractionation more closely approaches that of inorganic calcite, indicating that the expected "vital effect" offset is reduced. We offer two possible testable explanations for this behavior; firstly, that isotopic fractionation can occur "out of equilibrium" in the lowest temperature range when the ostracods moulted close to their torpidity limit and, secondly, that the culture solution pH has exerted an influence on the δ18O value of the ostracod calcite. If the pH of lacustrine waters is a significant control on ostracod- calcite δ18O values, their paleoenvironmental interpretation will be more complicated than heretofore appreciated.

    Original languageEnglish
    Title of host publicationThe Ostracoda
    Subtitle of host publicationApplications in Quaternary Research, 2002
    EditorsAllan R. Chivas, Jonathan A. Holmes
    PublisherBlackwell Publishing Ltd
    Pages301-313
    Number of pages13
    ISBN (Electronic)9781118668689
    ISBN (Print)9780875909905
    DOIs
    Publication statusPublished - 2002

    Publication series

    NameGeophysical Monograph Series
    Volume131
    ISSN (Print)0065-8448
    ISSN (Electronic)2328-8779

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