Traces of past oceanic and environmental conditions are stored in deep sea sediments as ‘proxy records’. When these ‘proxy records’ are deciphered, they can contain valuable information that can be used to reconstruct past chemical and physical conditions of the ocean throughout time. Though, these records can be distorted by a variety of chemical, physical, and biological processes including bioturbation, dissolution, and variations in sedimentation rate, complicating the relationship between stratigraphic depth and age of a geochemical proxy, and making it more difficult to translate past climates and environments. As CO2 levels continue to rise in our atmosphere, an understanding of how past extreme warming events, such as the Paleocene-Eocene Thermal Maximum (PETM, ~55.9 Ma), impacted environmental conditions and ecosystem dynamics can better inform how our modern ocean ecosystems will react to anthropogenic warming. During the PETM, a rapid injection of isotopically light carbon into the ocean and/or atmosphere, indicated by a negative carbon isotope excursion (CIE), resulted in global warming, changes in ocean ecosystem dynamics including a severe benthic foraminifera extinction, and global dissolution of deep-sea carbonates due to shoaling of the calcite compensation depth (CCD). This subsequent dissolution erased the onset of the PETM CIE at many deep sea locations, while the impact on the deep sea macrobenthic community remains unexplored. In this dissertation I investigate the response of the deep sea benthic and infaunal macrofauna response to the PETM by quantifying bioturbation intensity utilizing the ichnofabric index (ii) by identifying and measuring trace fossil community change in 46 deep sea sediment cores. I find global decreases in trace fossil community size, with over half of the locations ceasing bioturbation following the onset of the PETM. I utilize a novel burrow-specific sampling technique to investigate the movement of bulk sediment within discrete trace fossils. I find the most significant impact on the geochemical record occurs in concurrence with the CIE. I utilize neodymium isotopes in the North Atlantic at IODP site U1403 to investigate circulation patterns and find no change from Southern dominated deep water formation throughout the PETM.

The Eocene-Oligocene Transition (EOT) from 35-33 Ma, centered at 33.9 million years ago (Ma), marks the transition from a Greenhouse to an Icehouse earth. It is associated with the appearance of bulk-feeding whales, and the widespread increase in opal sedimentation in the earliest Oligocene, and has been interpreted to record the initiation of a highly productive Southern Ocean ecosystem. We measured accumulation rates of pelagic fish teeth and shark denticles (ichthyoliths) in a global array of ocean cores that span the EOT to test the impact of this transition on mid-level pelagic consumers, which could serve as trophic links between the opal-producing diatoms and larger, predatory whales. We find that there is no increase in fish productivity across the Eocene Oligocene Transition in any of our records; indeed, few records show any changes in fish production associated directly with the E/O boundary or the Oi-1 glaciation event at 34 Ma. Moreover, we find that export productivity was lower in our Southern Ocean sites compared to lower latitude sites in both the Atlantic and tropical Pacific for the duration of the records. Ecosystem models predict that diatom-based food webs should support abundant top predators. However, with reduced fish productivity, we speculate that diatoms instead formed the base of a food web which short-circuited fishes, perhaps feeding krill and other seasonally blooming zooplankton that in turn directly supported seasonally present top predators such as large whales.