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Johannes Gutenberg Universität Mainz

1. Yan, Lina. Calibration study of bivalve shells : implications for paleoenvironmental reconstruction.

Degree: 2013, Johannes Gutenberg Universität Mainz

The accretionary shells of bivalve mollusks can provide environmental information, such as water temperature, precipitation, freshwater fluxes, primary productivity and anthropogenic activities in the form of variable growth rates and variable geochemical properties, such as stable oxygen and carbon isotopes. However, paleoenvironmental reconstructions are constrained by uncertainties about isotopic equilibrium fractionation during shell formation, which is generally acknowledged as a reasonable assumption for bivalves, but it has been disputed in several species. Furthermore, the variation in shell growth rates is accepted to rely on multiple environmental variables, such as temperature, food availability and salinity, but can differ from species to species. Therefore, it is necessary to perform species-specific calibration studies for both isotope proxies and shell growth rates before they can be used with confidence for environmental interpretations of the past. Accordingly, the principal objective of this Ph.D research is to examine the reliability of selected bivalve species, the long-lived Eurhomalea exalbida (Dillwyn), the short-lived and fast growing species Paphia undulata (Born 1778), and the freshwater mussel Margaritifera falcata (Gould 1850), as paleoenvironmental proxy archives.rnThe first part is focused on δ18Oshell and shell growth history of live-collected E. exalbida from the Falkland Islands. The most remarkable finding, however, is that E. exalbida formed its shell with an offset of -0.48‰ to -1.91‰ from the expected oxygen isotopic equilibrium with the ambient water. If this remained unnoticed, paleotemperature estimates would overestimate actual water temperatures by 2.1-8.3°C. With increasing ontogenetic age, the discrepancy between measured and reconstructed temperatures increased exponentially, irrespective of the seasonally varying shell growth rates. This study clearly demonstrates that, when the disequilibrium fractionation effect is taken into account, E. exalbida can serve as a high-resolution paleoclimate archive for the southern South America. The species therefore provides quantifiable temperature estimates, which yields new insights into long-term paleoclimate dynamics for mid to high latitudes on the southern hemisphere.rnThe stable carbon isotope of biogenic carbonates is generally considered to be useful for reconstruction of seawater dissolved inorganic carbon. The δ13Cshell composition of E. exalbida was therefore, investigated in the second part of this study. This chapter focuses on inter-annual and intra-annual variations in δ13Cshell. Environmental records in δ13Cshell are found to be strongly obscured by changes in shell growth rates, even if removing the ontogenetic decreasing trend. This suggests that δ13Cshell in E. exalbida may not be useful as an environmental proxy, but a potential tool for ecological investigations. rnIn addition to long-lived bivalve species, short-lived species that secrete their shells extremely fast, can also be useful for environmental…

Subjects/Keywords: Bivalven Sklerochronologie; Paläoklima; Stabile Kohlenstoff- und Sauerstoffisotope; Bivalve sclerochronology; Paleoclimate; Stable carbon and oxygen isotopes; Paleontology Paleozoology

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APA (6th Edition):

Yan, L. (2013). Calibration study of bivalve shells : implications for paleoenvironmental reconstruction. (Doctoral Dissertation). Johannes Gutenberg Universität Mainz. Retrieved from http://ubm.opus.hbz-nrw.de/volltexte/2014/3613/

Chicago Manual of Style (16th Edition):

Yan, Lina. “Calibration study of bivalve shells : implications for paleoenvironmental reconstruction.” 2013. Doctoral Dissertation, Johannes Gutenberg Universität Mainz. Accessed October 19, 2019. http://ubm.opus.hbz-nrw.de/volltexte/2014/3613/.

MLA Handbook (7th Edition):

Yan, Lina. “Calibration study of bivalve shells : implications for paleoenvironmental reconstruction.” 2013. Web. 19 Oct 2019.

Vancouver:

Yan L. Calibration study of bivalve shells : implications for paleoenvironmental reconstruction. [Internet] [Doctoral dissertation]. Johannes Gutenberg Universität Mainz; 2013. [cited 2019 Oct 19]. Available from: http://ubm.opus.hbz-nrw.de/volltexte/2014/3613/.

Council of Science Editors:

Yan L. Calibration study of bivalve shells : implications for paleoenvironmental reconstruction. [Doctoral Dissertation]. Johannes Gutenberg Universität Mainz; 2013. Available from: http://ubm.opus.hbz-nrw.de/volltexte/2014/3613/

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