Stable Carbon And Oxygen Isotope Composition Of Bivalve Shells As Typomorphic Characters Of Ambient Environment

Aragonite is the main mineral composition of bivalve shells, which contains a lotof information about bivalve life history and ambient environment. Detailed study ofestablishment of environmental typomorphic characteristics (such as carbon andoxygen isotopes, etc.) is helpful for better understanding of past climate environment.The dissertation focuses on Paphia undulata (Born,1778) from the south China seaand Eurhomalea exalbida (Dillwyn,1817) from the southwest Atlantic, and putsforward the necessity of calibration study using modern shells, and further establishesthe useful typomorphic characteristics of environment (carbon and oxygen isotopeproxies); In addition, fossil shells from Holocene period provide important evidencefor the ancient climate events, including summer monsoon intensity of RomanOptimumand Little Ice Age, cold event of4000BP, and cold event of5500BP. Theclimate of South China Sea is mainly affected by the Asian monsoon system. In orderto study short time scale changes of past Asian monsoon, and evaluate and establishclimate archives of Asian monsoon changes, calibration study of P. undulata shellfrom Daya bay of SCS has been carried out. The results show that the shell growsuninterruptedly from March to mid November and are formed near oxygen isotopicequilibrium with the ambient environment. Shell stable carbon isotope values likelyreflect the relative amount of isotopically light terrestrial carbon that reaches theocean during the summer monsoon season. Therefore, shells of this species canprovide reliable, sub-seasonally resolved data on past Asian summer monsoonstrengths. As the typomorphic characteristics of monsoon climate，oxygen isotopicdata of fossil P. undulata has a considerable potential, and its high resolution data canprovide the frequency of exceptional summer monsoons. The study on E. exalbidafrom the Southwest Atlantic clearly demonstrates that, when the disequilibriumfractionation effect is taken into account, E. exalbida can serve as a high resolutionpaleoclimate archive for the southern South America. The species therefore providesquantifiable temperature estimates, which yields new insights into long termpaleoclimate dynamics for mid to high latitudes on the southern hemisphere. Oxygen isotopic data of fossil shells suggest that the species may experience the cold event inmiddle Holocene (5500BP), thus providing evidence to cold events of the past. Studyon different species from different water environments demonstrates that the bivalvespecies have strong species dependence during mineralization. Therefore, calibrationstudy using modern shells is indispensable for paleoclimate and paleoenvironmentstudy. In addition, it is of great significance for solving the species-dependentproblem and for establishment of the global digital climate models using differentspecies from the same water, and the same species from different regions, andmulti-species from multi-regions.