Deep-sea ostracoda faunal dynamics across evolution of the cenozoic climate

Abstract

Cenozoic icehouse climate is characterized by a 45-million-year progressive cooling, development of a glacial earth, orbital climate variability, and enhanced Arctic amplification. Current climate change is threatening marine biota through warming, deoxygenation, and other factors involving processes such as the Arctic amplification. However, an unresolved key question is the detailed biotic responses to various scales and rates of environmental changes. To improve our understanding on this topic, I focus on deep-sea ecosystems under a comprehensive framework of climate, ocean, and timescale perspectives, and Ostracoda as a model organism. I conducted ostracod microfaunal analyses using marine sediment cores in multiple ocean systems spanning evolution of the Cenozoic icehouse climate, specifically across the Eocene/Oligocene boundary, the middle Pleistocene climate events, and the last 2-million-year glacial-interglacial cycles. The results show that at a long-term macroevolutionary scale, global diversity patterns of deep-sea ostracods met a major threshold around the Eocene-Oligocene onset of the icehouse climate. Across secular-scale Pleistocene climate events (i.e. the Mid-Pleistocene Transition and the Mid-Brunhes Event) involving amplified glacial variability, benthic fauna in multiple seas show various responses, including extinctions of certain groups and faunal transitions associated with temperature changes or sea-ice development. In the Sea of Japan marginal ocean system, numerous orbital-scale cycles of extirpation events occurred due to deoxygenation, and opportunistic species dominated during transitional stages. This thesis demonstrates the sensitivity and vulnerability of deep-sea ecosystems at various temporal and spatial scales, especially with respect to the current concerns about deoxygenation and Arctic amplification. Future work on evolutionary processes of marine biodiversity patterns is needed to provide important insight into the assessment of current threats from anthropogenic impacts.