Biotic Change and Landlocked Seas: Ecosystem responses to climate and sea level variability in the Plio-Pleistocene of the Pontocaspian basins

Abstract

This thesis aims to understand the response of ecosystems to changes in climate and sea level in the Black Sea and Caspian Sea (Pontocaspian region) over the past 5.3 million years. The focus of the research is primarily on two groups of organisms that can easily be traced through the fossil record: land plants, such as trees, shrubs and herbs (which leave fossils in the form of pollen grains), and marine planktonic microorganisms, such as dinoflagellates and microalgae. Part of this thesis is devoted to developing methods for use in the study of past climate and ecosystems, and also to developing approaches to challenging areas, such as refining classification of dinocyst species from geological deposits. The Black Sea became connected to, and then disconnected from, the Mediterranean Sea several times during the last 430,000 years. These switches affected dinoflagellate communities, causing extinctions, disappearances and reappearances of certain species over time. We also demonstrate a major disruption to dinoflagellate communities caused by the flooding of marine water into the Caspian Sea at a time known as the Plio-Pleistocene transition (approx. 2.7 million years ago). Current evidence suggests that the source of the water could have been the Arctic Ocean. Conversely, the flooding appears to have had a moderating effect on land plants, providing moisture needed to sustain broad leaved forests even at a time of cooling and drying of climate globally. This demonstrates the importance of landlocked seas in controlling environments in the central parts of large landmasses such as Eurasia.