From Continental Margins to the Deep Ocean

Oxygen minimum zones (OMZs) occupy ~9% of the ocean but strongly influence marine biogeochemical cycles. The response of these zones to climate change is uncertain, making reconstructions of past redox conditions, to better understand the future, essential. For this porpose, redox-sensitive proxies are widely used, but their signals can be altered by depositional and diagenetic processes. In this thesis, we investigate the behavior of these redox proxies. This thesis examines three environments: the Peruvian Margin (continental margin), the Guaymas Basin (semi-restricted), and Pacific Gyres (oxic pelagic, ~90 Myr). Proxies such as iron speciation, Mo and U concentrations, and isotopes (δ98Mo, δ15N) were used to reconstruct redox conditions and assess proxy reliability. Results show that proxies are not always straightforward indicators of bottom-water redox. In pelagic sediments, δ98Mo is not preserved over long timescales and can be altered by hydrothermal input. In the Guaymas Basin, high FeHR/FeT reflects diagenetic pyritization rather than euxinic conditions. On the Peruvian Margin, elevated FeHR/FeT and U values are influenced by terrigenous input and lateral transport, not solely redox conditions. After accounting for these effects, clearer patterns emerge. At Site 680, Mo accumulation varied over ~620 kyr, with particulate control during interglacials and diffusion during glacials. Site 679 records stronger Pliocene anoxia linked to tectonic changes, while Site 682 shows a shift to better oxygenation over time. In the Guaymas Basin, past anoxia was stronger than today, with Mo mainly controlled by diffusion. Overall, diagenesis, terrigenous input, and lateral transport can obscure primary redox signals, and must be considered for reliable paleoceanographic reconstructions.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Christian-Albrechts-Universität zu Kiel

Year

2026

Author dc:creator

• Fraga Ferreira, Paula Luiza

Contributors dc:contributor

• Frank, Martin
• Scholz, Florian

• Redox proxies
• Paleoenvironment
• Oxygen; Isotopes
• Molybdenum
• Uranium
• Iron Speciation
• Peruvian Margin
• Guaymas Basin
• Oxygen Minimum Zone
• Pelagic Clays
• Deep Sea Sediments

Repository record source_url

https://macau.uni-kiel.de/receive/macau_mods_00008109

OAI identifier oai:identifier

oai:macau.uni-kiel.de:macau_mods_00008109