| Summary: | <p> Evidence from modern oceanography, climate simulations of future conditions, and paleoceanographic archives motivates the need to reconstruct Oxygen Minimum Zone (OMZ) changes during past events of abrupt climate warming and carbon system perturbation. This dissertation focuses on the loss of oxygen in the Eastern Pacific Ocean through the most recent deglaciation event, in order to understand the spatial magnitude of oceanic deoxygenation and to quantify disturbance and recovery dynamics in seafloor biodiversity. New evidence from a shallow post-glacial sediment core (MV0811-15JC) from Santa Barbara Basin, California, USA, demonstrates the remarkable shallowness of OMZ influence to within ~300 meters from the ocean surface during the recent deglaciation. This site confirms that paleoceanographic reconstructions of hypoxia from Santa Barbara Basin are a product of regional expansions and contractions of the OMZ. Microfossil archives of seafloor metazoans (Echinodermata, Arthropoda and Mollusca; >5,350 individuals) from site MV0811-15JC demonstrate the extreme sensitivity of seafloor metazoan communities to abrupt (<100 year) deoxygenation of the Eastern Pacific, and expand known timescales of biological recovery by one order of magnitude, from <100 years to >1,000 years. Molluscan communities provide a complex interpretive window with which to understand environmental change through the deglaciation. Chemosynthetic and symbiotic molluscs numerically dominate the faunal record, yet these extremophiles do not strongly co-occur, indicating the development of heterogeneous extreme environments as a result of hydrographic regimes and the development of sulfur oxidizing bacterial mats. These analyses reveal that previous deoxygenation events dwarf modern scales of ecological disturbance, and illustrate the role that climate and oceanographic change have in driving long-term successional oscillations in ocean ecosystems. More broadly, the global inventory of deglacial and post-glacial sediment records exhibits remarkable synchrony in reconstructing subsurface hypoxia, and reveals that OMZs across the entire Eastern Pacific margin expanded and intensified concurrently. Most strikingly, these results uncover the capacity for large contiguous swaths of the ocean interior to rapidly lose dissolved oxygen, resulting in the expansion of OMZ ecosystems and the compression of surface ocean oxygenated ecosystems. Climate-forced changes to ocean systems introduce a scale of environmental disturbance that only has analogue in the rapid warming events of past climates. These critical analogues serve to illustrate the scale and ecological consequences of climate-forced deoxygenation.</p>
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