Biogeochemistry of Oceanic Euxinia in Earth History: Numerical Modeling and Evaluation of Biomarkers Using Modern Analogs
Open Access
- Author:
- Meyer, Katja Maria
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 19, 2008
- Committee Members:
- Lee Kump, Dissertation Advisor/Co-Advisor
Lee Kump, Committee Chair/Co-Chair
Katherine Haines Freeman, Committee Chair/Co-Chair
Jennifer Macalady, Committee Member
John Michael Regan, Committee Member - Keywords:
- euxinia
Earth system model
Permian-Triassic boundary
mass extinction
hydrogen sulfide
carotenoid
biomarker - Abstract:
- The present study is a multi-disciplinary exploration of the overarching factors that contribute to oceanic euxinia and its sedimentary signature. Using the GENIE Earth system model, I investigated the physical and chemical factors that enhance euxinia in the geological record. Sustained global warmth, ocean circulation patterns replete with nutrient-trapping geographies, and elevated nutrient conditions initiate biological feedbacks that stimulate euxinia based on this numerical analysis. I then use the example of the end-Permian, an interval during which euxinia and mass extinction coincide, to further explore the biogeochemical controls on the buildup of sulfide in the global ocean. With the end-Permian configuration of GENIE, I examine the distribution of H2S accumulation in the ocean and quantify the impact of anoxygenic phototrophy in reducing surface-water [H2S] under a range of oceanic phosphate conditions. The modeled spatial predictions largely agree with the geological record of geochemical and biotic change across the Permian-Triassic boundary. Addition of a nitrogen cycle to GENIE results in further reduction of hydrogen sulfide buildup. The high productivity euxinic ocean is N-limited as evidenced by low N:P ratios in the deep ocean. This work serves as a quantitative basis for linking the fossil record of extinction to the geochemical record of carbon and sulfur cycle perturbation. The geologically stable remnants of carotenoids from the anoxygenic green and purple sulfur bacteria are a powerful method of identifying photic zone euxinia in the rock record. I used pigment and clone library analyses from planktonic and benthic samples collected in a microbially dominated meromictic lake (Fayetteville Green Lake, New York) to test the hypothesis that the purple sulfur bacterial carotenoid, okenone, is only produced in planktonic settings. We report evidence of okenone and purple sulfur bacteria in both benthic and planktonic environments of Fayetteville Green Lake. This finding highlights the need for continued study of modern environments and the physiology of carotenoid expression in modern microbes to aid interpretation of biomarkers for photic zone euxinia in the geological record.