The role of volcanism in rapid global climate change events of the Paleogene

The greenhouse climate of the Paleogene was punctuated by transient hyperthermals, distinguished by negative carbon isotope excursions in the sedimentary record and rapid global warming. From ~50 Ma, the climate deteriorated into the Oligocene, with abrupt global cooling and ice sheet formation marking the Eocene-Oligocene transition (EOT). Research on large igneous provinces (LIPs) demonstrates their potential climate forcing ability: i) global warming through direct CO₂ input into the atmosphere and/or thermal alteration of organic-rich rocks by magmatic intrusions, and ii) global cooling by the rapid weathering of volcanic products and/or inciting changes in marine productivity (intensifying CO₂ drawdown). The North Atlantic Igneous Province (NAIP) was active during the late Paleocene–early Eocene, and the Afro-Arabian and Sierre Madre Occidental siliceous LIPs were active during the late Eocene–early Oligocene, presenting a potential connection to be explored between volcanism and Paleogene rapid climate change.

Mercury (Hg) is a trace component emitted during volcanic eruptions which can be globally distributed, deposited into the oceans, and transferred into sediments. To interpret volcanic-derived Hg anomalies, the sediment host phase of Hg must be considered to resolve changes in host phase concentrations. Organic matter and sulfides are the dominant Hg host phases, therefore this thesis analyses Hg/TOC and Hg/TS ratios in marine sediments. Osmium isotope ratios (¹⁸⁷Os/¹⁸⁸Os_(i)) are used to track seawater chemistry changes related to silicate weathering. This thesis finds no volcanic-derived (normalised) Hg at the EOT, and consequently, no evidence of volcanic forcing on climate. Similarly, there were no pronounced volcanic Hg/TOC or Hg/TS peaks around the early Eocene hyperthermals, and therefore no evidence of NAIP volcanic activity influencing climate at the onset of these events. However, unradiogenic Os isotope shifts occur prior to hyperthermal Eocene Thermal Maximum 2 (ETM2/H1) and the J event, which is interpreted as the weathering of previously emplaced NAIP volcanic deposits. The PETM demonstrated significant Hg, Hg/TOC and Hg/TS values, which are interpreted as volcanic signals from the NAIP to an extent, but significantly enhanced and altered by post-depositional processes.