| This dissertation is composed of three individual studies that further our knowledge of the carbon cycle through three themes: (1) biological production and particle transport, (2) sedimentation, and (3) ocean circulation and climate. Paleoredox and paleoproductivity tracers are applied to marine sediments on both long (106 years) and short (104 years) timescales at a variety of locations throughout the ocean basins.;In chapter one, I documented the biological production and particle transport at Ocean Drilling Program (ODP) Site 1237 in the Southeast Pacific. This study traced the past 30 Myr record and tectonic evolution of Nazca Ridge as this fossil hotspot moved from the Oligotrophic open-ocean to the coastal upwelling region off Peru. I show that increases in concentrations of phosphorus (P) and biogenic barium (bio-Ba), tracers of nutrient burial and export productivity, respectively, coincide with the site moving closer to South America. A color change roughly in the middle of the stratigraphic section is associated with a shift in the elemental ratios of the paleoredox tracers manganese (Mn) and uranium (U). This is likely a relict redox boundary with oxygenated conditions below and more reducing bottom-waters above.;Chapters two and three focus on a transient perturbation to the carbon cycle that induced global greenhouse warming. This event occurred ∼55 million years ago and is known as the Paleocene-Eocene thermal maximum (PETM). The thermal dissociation of methane hydrates is the most plausible source of warming. Release of methane in the oceans oxidizes to carbon dioxide, depleting available bottom-water oxygen concentrations.;Chapter two focuses on sedimentation and variations in the oxidation state of the sediment-water interface across the PETM. I measured Mn and U in cores from a depth transect of sites in the Southeast Atlantic on Walvis Ridge (ODP Leg 208, Sites 1262, 1263, and 1266). During the PETM, the deep and intermediate sites shift from oxygenated bottom-waters to more reducing conditions, then return to oxygenated in the recovery. The shallowest site displays reducing conditions throughout the sampled interval and may have been situated in an oxygen minimum zone.;In chapter three, I apply the paleoredox tracers to a suite of sites representing the global ocean basins during the PETM. I test the hypothesis that methane release occurred in the Atlantic Ocean and comment upon the possibility of reversed deep ocean circulation during this event. My results indicate that intermediate water depth sites in the Atlantic are the most reducing and are probably closest to the site of methane hydrate release, while sites furthest from the source (Pacific locations) are well oxygenated. The gradient in oxidation state of bottom-waters between the Atlantic and Pacific support a transient reversal in deep-ocean circulation relative to modern. |
