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Calibration Study of Bivalve Shells – Implications for Paleoenvironmental Reconstruction

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Calibration Study of Bivalve Shells – Implications for Paleoenvironmental Reconstruction Calibration study of bivalve shells – implications for paleoenvironmental reconstruction Dissertation zur Erlangung des Grades “Doktor der Naturwissenschaften“ im Promotionsfach Geologie/Paläontologie am Fachbereich Chemie, Pharmazie und Geowissenschaften der Johannes Gutenberg-Universität Mainz von Lina Yan geb. in Heilongjiang, China Mainz, 2013 Berichterstatter: Berichterstatter: Datum der mündlichen Prüfung: 16th December 2013 II DECLARATION I hereby declare on my honor that the thesis submitted is my own work except for quotations which have been listed in the References. Ich erkläre hiermit, dass ich die vorliegende Arbeit selbständig verfasst und keine anderen als die angegebenen Quellen und Hilfsmittel benutzt habe. Signature: Date: Place: III PREFACE With curiosity for the world and desire for knowledge, I landed in Frankfurt airport and started my Ph.D. study in Palaeotological group under the supervision of Prof. Dr. ***, in the University of Mainz at 01st September 2010. During the three years, I have been kept working on bivalve mollusk shells, which contain a wealth of environmental, climatic, and life history information, preserved as physical and chemical variations within the shells. Bivalve mollusk sequentially secrets its shell with periodicity, such as the annual, fortnightly and daily increments, recording the growth histories, metabolism and environmental conditions experienced during the deposition of that shell material. Furthermore, bivalve shells can preserve life history and environmental information during their growth as variations in 18 13 geochemistry, such as oxygen and stable carbon isotopes (δ Oshell and δ Cshell). Distinct shell growth structures, i.e. growth increments and growth lines, can enable precise calendar dating of each successive band of shell periodic accretion and estimation of ontogenetic age. Micro- 18 sampling technique of shell cross sections provides a means of high-resolution δ Oshell and 13 δ Cshell proxies for bivalve archives, which is essential to better understand processes and mechanisms of environmental changes in seasonal or sub-seasonal time scale. This Ph.D. dissertation has four main components, with one publication and one submission in high-impact, peer-reviewed journals, one prepared draft and one chapter with the preliminary results. The first paper, which has been published in Palaeogeography, 18 Palaeoclimatology, Palaeoecology, investigates if δ Oshell of the long-lived marine bivalve Eurhomalea exalbida can serve as a faithful proxy of temperature in southern South America. The second paper, a well-prepared draft, focuses on variations in inter-annual (ontogenetic) and intra- 13 13 annual (seasonal) δ Cshell to examine if δ Cshell in E. exalbida is a servable indicator of ambient environments on the basis of sclerochronology and environmental comparisons. The third paper, submitted to the Journal of oceanography, presents the detailed analysis of the life history traits, 18 13 δ Oshell and δ Cshell records of the short-lived marine bivalve Paphia undulata. The objective is to evaluate if shells of this species can provide reliable, sub-seasonally resolved data on past East Asian summer monsoon strengths, and to exploit the possibility into predictions of future monsoon-related climate extremes in SE Asia. Additionally, preliminary investigations on the freshwater pearlshells Margaritifera falcata are presented in the last part, which is meant to provide environmental implications on population age structures and shell growth rates of the freshwater mussel. IV This research includes the efforts of some other co-authors, especially Prof. Dr. ***. I would like to express my gratitude to his constructive comments and plenty of time spent on corrections to improve my writing. “Be always critical of your own data” is his famous words, which benefits me a lot in science. Furthermore, I would like to acknowledge the Chinese Scholarship Council (CSC) and the Earth System Research Centre-Geocycles (Johannes Gutenberg-University of Mainz), which makes this research project possible. I would also like to thank the providers of my study material and all the people who contributed to this study here. Signature: Date: Place: V ABSTRACT 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. 18 The first part (Chapter 2) is focused on δ Oshell and shell growth history of live-collected E. exalbida from the Falkland Islands (Southwest Atlantic). Results indicate that E. exalbida likely captures the full seasonal temperature amplitude in its shell. Annual growth line formation occurs between fall and early winter. 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. The stable carbon isotope of biogenic carbonates is generally considered to be useful for 13 reconstruction of seawater dissolved inorganic carbon. The δ Cshell composition of E. exalbida was therefore, investigated in the second part (Chapter 3) of this study. This chapter focuses on 13 inter-annual (ontogenetic) and intra-annual (seasonal) variations in δ Cshell. A decreasing trend in 13 δ Cshell is observed through ontogeny, as well as evident seasonal cycles in all studied specimens. 13 This decreasing trend and the seasonal cycles in δ Cshell both appear to be linked to the variations VI in shell growth rates, which can be attributed to the inverse correlation between the mantle 13 metabolic activity and shell growth rates. Furthermore, environmental records in δ Cshell are found to be strongly obscured by changes in shell growth rates, even if removing the ontogenetic 13 decreasing trend. This suggests that δ Cshell in E. exalbida may not be useful as an environmental proxy, but a potential tool for ecological investigations. In addition to long-lived bivalve species, short-lived species that secrete their shells extremely fast, can also be useful for environmental reconstructions, especially as a high- resolution recorder. Therefore, P. undulata from Daya Bay, South China Sea (SCS) was utilized in Chapter 4 to evaluate and establish a potential proxy archive for past variations of the East Asian monsoon (EAM) on shorter time-scales. Results indicate that this species lived for only three years and secreted their shells uninterruptedly between March and mid November near 18 oxygen isotopic equilibrium with the ambient environment. The δ Oshell can provide qualitative 13 estimates of the amount of monsoonal rain and terrestrial runoff and the δ Cshell likely reflect the relative amount of isotopically light terrestrial carbon that reaches the ocean during the summer monsoon season. Therefore, shells of P. undulata can provide serviceable proxy archives to reconstruct the frequency of exceptional summer monsoons in the past. The relative strength of 13 monsoon-related precipitation and associated changes in ocean salinity and the δ C ratios of the 13 18 13 dissolved inorganic carbon signature (δ CDIC) can be estimated from the δ Oshell and δ Cshell values as well as shell growth patterns. In the final part (Chapter 5) of this thesis, the freshwater pearl shell M. falcata from four rivers in British Columbia, Canada was preliminarily studied concerning the lifespans and the shell growth rates. Two groups separated by the Georgia Strait can be clearly distinguished. Specimens from the western group (Piercy Creek River and Chase River) exhibit a shorter lifespan, while the eastern group (Salmon River and Little Campbell River) live longer. Moreover, the average lifespan seems
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