Stable Isotope Geochemistry of Shelled Marine Invertebrates: Wide-Ranging Applications

Mollusks grow by adding discrete growth layers throughout their lifetime (i.e., accretion). More specifically, most marine mollusks precipitate their shells in oxygen isotopic equilibrium with seawater or with a constant offset from equilibrium. The stable oxygen isotope values (δ18O) of their shells are determined by the temperature and δ18O values of the surrounding water during calcification without significant vital effects. In comparison, the stable carbon isotope values (δ13C) of their shells reflect those of the dissolved inorganic carbon (δ13C- DIC) and respired carbon dioxide. Therefore, variations in the oxygen and carbon isotope composition of the accretionary skeletons of mollusks should record a plethora of temporal information about the hydrological conditions and nutrient sources they have experienced throughout their lifetime. In Chapter One, stable oxygen and carbon isotopic compositions were analyzed in sclerochronological profiles of late Pliocene-to-modern shells of the venerid bivalve genus Chione in south Florida to infer any temporal changes in age-at-death and maturation time using the profiles as proxies of life history changes. This chapter aimed to test the hypothesis that the rise of Chione bivalve-dominated assemblages at the Plio-Pleistocene fossil record was a real ecological event and not a taphonomic artifact driven by a life history change. In Chapter Two, marine gastropod shells of the Strombus alatus species complex in south Florida were analyzed for their shell δ18O and δ13C values to investigate the timing, magnitude, and direction of changes in paleoenvironmental conditions since the late Pliocene, a period of accelerated environmental and biotic change for Florida\u27s marine ecosystems. The stalked barnacle Lepas anatifera has multiple calcitic plates that also grow by accretion. Therefore, the analysis of the plates\u27 oxygen and carbon isotopic composition in sclerochronological profiles should provide information about the water temperature experienced by the barnacles throughout their lifetimes. In Chapter Three, calcite δ18O values of L. anatifera shells reared under controlled laboratory conditions were used to develop an empirically-derived paleotemperature equation. The relationship was then used with published δ18O data of L. anatifera barnacles that were found attached to a beached flaperon in Reunion Island, which was identified as belonging to the missing Malaysian airplane flight MH370, to backtrack the drifting path of the flaperon before its arrival to the island. This dissertation explores multiple applications of stable oxygen and carbon isotope geochemistry of shelled-marine mollusks (bivalves and gastropods) and crustaceans (barnacles). The results reported in Chapter One and Chapter Two provide valuable information for understanding spatial and temporal changes in paleoenvironmental conditions in south Florida since the late Pliocene. Similarly, the findings of Chapter Three demonstrate how the geochemistry of the calcitic plates of the stalked barnacle L. anatifera is potentially useful as geochemical tracking devices in the open ocean