Toward quantifiable temperature reconstructions from bivalve shells
Zusammenfassung der Projektergebnisse
Goal of present study was to establish new means for reliable and quantitative temperature reconstructions from mollusk shells. For this purpose, experiments with living animals were conducted in a series of lab and field experiments during which relevant environmental variables were closely monitored. Experiments were conducted with specimens from freshwater, brackish and fully marine environments. Main results are as follows. (1) Shell microstructure react sensitive to environmental stress. Temperatures beyond speciesspecific optimum conditions resulted in an increased number of disturbance lines in the freshwater gastropod Viviparus viviparus. These lines differ structurally from adjoining shell portions and are typically made of irregular simple prismatic microstructures, i.e., evolutionarily the most primitive shell architectures. (2) Temperature stress resulted in overall microstructures that differed vastly from those formed under optimum conditions. Instead of slim and slender first order lamellae, stressed specimens of V. viviparus formed broad, ramified first order lamellae. However, these aberrant structures were only formed during de novo fabrication of biominerals. On preexisting aragonite, subsequently deposited shell was structurally invariant. (3) Under low-oxygen and low-salinity conditions, Arctica islandica forms thinner shells (inner layer and portion of the middle layer dissolved) with a larger number of disturbance lines. The typical shell microstructure is difficult to recognize, because a greater amount of organic matrices is present in such specimens. (4) A clear link exists between the element chemistry and architecture of the shell. Trace impurities are highly heterogeneously distributed in the shells. For example, portions consisting of irregular simple prismatic microstructures such as annual and daily growth lines tend to be enriched in certain trace elements including Sr. Chemical analyses should ideally be confined to structurally similar shell portions (and the same shell layer) and portions with a more uniform microstructure (e.g., the hinge plate). (5) Despite biological controls on the incorporation of trace impurities in the shells, Sr/Cashell values of Arctica islandica (fully marine, nature), Corbicula fluminea (freshwater, lab experiment) and Cerastoderma edule (brackish, nature) are clearly negatively correlated to ambient water temperature (provided that samples were taken in structurally identically shell portions). In these species, ca. 40 to 45% of the variability in Sr/Cashell is typically explained by temperature changes. Crystal growth kinetics and growth rate (food supply) have no statistically relevant influence on the Sr/Cashell vs. temperature relationship. (6) Li/Cashell and, in particular, Sr/Lishell values of Cerastoderma edule may serve as even better temperature proxies than Sr/Cashell. More than 80% explained variability was found. (7) The carbonate clumped isotope thermometer does not seem to work well in shells of Cerastoderma edule. ∆47-based temperature estimates greatly exceeded maximum recorded temperatures during the growing season. (8) Na/Cashell of Arctica islandica does not co-vary with salinity. Instead, we not only observed a considerable variability of Na/Cashell data among contemporaneous specimens and a large scatter, but also significant differences between time-series taken from single specimens. (9) Physical and chemical pre-treatment methods can significantly influence light stable isotope values. Great care must be taken that chemical analyses are completed on pure shell material. Future studies need to verify the findings of this project using other mollusk species. Chemical analyses of mollusk shells should be accompanied by a detailed description of the shell microstructure. Morphological and crystallographical properties of biomineral units potentially contain information of ambient temperature. Future studies should explore the usefulness of this proxy. Results obtained during lab experiments should be verified by field studies.
Projektbezogene Publikationen (Auswahl)
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2013. Arctica islandica (Bivalvia): A unique paleoenvironmental archive of the northern North Atlantic Ocean. Global and Planetary Change 111, 199-225
Schöne BR
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2014. Assessment of the mechanism of elemental incorporation into bivalve shells (Arctica islandica) based on elemental distribution at the ultrastructural scale. Geochimica et Cosmochimica Acta 126, 307-320
Shirai K, Schöne BR, Miyaji T, Radermacher P, Krause RA Jr and Tanabe K
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2014. Microstructures in shells of the freshwater gastropod Viviparus viviparus: A potential sensor for temperature change? Acta Biomaterialia 10, 3911-3921
Füllenbach CS, Schöne BR and Branscheid R
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2015. Strontium/lithium ratio in shells of Cerastoderma edule (Bivalvia) - A new potential temperature proxy for brackish environments. Chemical Geology 417, 341-355
Füllenbach CS, Schöne BR and Mertz-Kraus R
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2016. Controls on strontium and barium incorporation into freshwater bivalve shells (Corbicula fluminea). Palaeogeography, Palaeoclimatology, Palaeoecology
Zhao L, Schöne BR and Mertz-Kraus R
