| Summary: | Tesis con mención internacional In order to accurately predict how organisms will respond to the rapidly changing climatic conditions, we need to understand how they adapted to past climate changes and why some of them became extinct. Marine phytoplankton are considered key climatic regulators, and among them, especially diatoms and coccolithophores, as it is through their photosynthetic activity that they modulate CO2 variability, while promoting carbon export from the surface ocean to the deep sediments via increasing ballasting efficiency. Diatoms are responsible for more than half of the global marine primary production, being the world¿s main biosolicificators, while coccolithophores are the main carbonate producers in the modern and past ocean, highly enhancing ballasting efficiency and carbon sequestration into the deep sediments. Given the reciprocal influence of diatoms and coccolithophores on climate, the geochemical analysis of their fossils can be used to trace the paleoceanographic history of certain oceanic regions, while providing information on their evolutionary response to past climate variations. In this thesis, the biominerals produced by coccolithophores and diatoms were used to apply the previously-calibrated coccolith Sr/Ca proxy to reconstruct paleoproductivity of the Atlantic sector of the Southern Ocean during the penultimate glacial cycle, to develop the new geochemical frustule B content proxy of diatom active bicarbonate uptake, and to develop and apply the coccolith Ca isotopic composition (¿44/40Ca) proxy to evaluate the mechanisms controlling coccolith Ca isotopic fractionation. Chapter I describes how the coccolith Sr/Ca paleoproductivity record of the Agulhas Bank slope (Atlantic sector of the Southern Ocean; core MD96-2080) during the penultimate glacial-interglacial cycle, provided information to resolve temporal changes in the westerlies¿ dynamics and clarify the role of obliquity in controlling their latitudinal displacement and strength. The productivity signal was ...
|
|---|