Constraining ocean acidification and anoxia during the end-Guadalupian and end-Triassic extinctions with calcium and uranium isotopes
Abstract/Contents
- Abstract
- Many mass extinctions are contemporaneous with emplacement of large igneous provinces (LIPs), suggesting that the environmental effects of LIP volcanism were important kill mechanisms. Of major interest is whether rapid injection of volcanic carbon dioxide into the ocean and atmosphere resulted in seawater acidification and eutrophication. The end-Guadalupian (ca. 260 Ma) and end-Triassic (ca. 201 Ma) extinctions were both associated with LIPs and saw preferential extinction of marine animals sensitive to changes in seawater pH or oxygen content. Carbon isotope fluctuations are consistent with some type of carbon cycle perturbation, and local proxies of acidification and anoxia are widespread. However, we have not yet been able to quantify the severity of acidification or anoxia during these events at a global scale. Calcium and uranium isotopes can be combined with carbon isotope data to constrain these phenomena. This is because the carbon cycle is linked to the calcium cycle via burial of calcium carbonate and chemical weathering of Ca-minerals, and to the uranium cycle via organic carbon production and precipitation of uranium under reducing conditions. For my dissertation, I use these non-traditional isotope systems, along with numerical models of their mass and isotopic fluxes, to constrain the cause of carbon cycle perturbations and the seawater geochemistry during each extinction. Chapter one discusses the end-Guadalupian extinction event. Contrary to claims of large carbon cycle perturbations during the end-Guadalupian extinction, calcium isotope data suggest that acidification was minimal and that carbon isotope excursions were generated or amplified by local conditions. This finding is consistent with much lower revised extinction rates based on new compilations of fossil occurrences. Chapters two and three discuss the end-Triassic extinction event. In contrast to the end-Guadalupian, the end-Triassic calcium isotope record contains a large (0.7‰) negative excursion just above the extinction horizon. Numerical modeling of the carbon and calcium cycles demonstrate that these patterns are consistent with acidification and enhanced calcium isotope fractionation due to higher precipitation rates during recovery from acidification. Uranium isotope data show similarly large perturbations, with a 0.6‰ negative isotope excursion suggesting a 35x increase in the extent of anoxic bottom waters following the end-Triassic extinction. Together, these projects demonstrate the power of combining non-traditional isotope systems with other proxies to constrain the nature of environmental change surrounding mass extinctions in the geologic record.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Jost, Adam Barrett |
|---|---|
| Associated with | Stanford University, Department of Geological Sciences. |
| Primary advisor | Payne, Jonathan L |
| Thesis advisor | Payne, Jonathan L |
| Thesis advisor | Lowe, Donald R, 1942- |
| Thesis advisor | Maher, Katharine |
| Advisor | Lowe, Donald R, 1942- |
| Advisor | Maher, Katharine |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Adam Barrett Jost. |
|---|---|
| Note | Submitted to the Department of Geological Sciences. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Adam Barrett Jost
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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