New Insights into the Marine Oxygen Cycle from Manganese Oxide Minerals and Reactive Oxygen Species

Kevin Sutherland, Ph.D., 2019
Colleen Hansel, Co-Advisor
Scott Wankel, Co-Advisor

The redox cycling of oxygen has profound influence on Earth’s climate and habitability. In this thesis, I explore two aspects of the marine oxygen cycle. First, I investigate the ability of manganese (Mn) oxide minerals to incorporate the oxygen isotopic signature of dissolved O₂ during Mn(II) oxidation. Using stabile isotope techniques, I measure the oxygen isotope fractionation factors associated with Mn oxidation, and determine that approximately half of the oxygen atoms in Mn(III,IV) oxides are incorporated from dissolved oxygen. I use triple oxygen isotope measurements to demonstrate that Mn oxides from the marine environment retain dissolved oxygen signatures for at least 30 million years. I next examine the role of dark, extracellular superoxide production by marine microbes in the marine oxygen budget. I measure superoxide production rates by abundant marine microbes and use these rates to estimate that extracellular superoxide production yields a net sink of 5‑19% of marine O₂. Lastly, I determine the fate of superoxide’s primary decay product, hydrogen peroxide, across a range of environmental conditions. Altogether, this thesis illuminates a path toward investigating the oxygen cycle on million-year timescales in Earth’s recent past and demonstrates the importance of microbial superoxide production in the biogeochemical cycling of O₂.