Marine Carbon and Sulfur Geochemical Cycling: Reassessing Sulfate Reduction and Anaerobic Oxidation of Methane
| dc.contributor.advisor | Dickens, Gerald R. | en_US |
| dc.contributor.committeeMember | Lee, Cin-Ty A. | en_US |
| dc.creator | Miller, Clint Matthew | en_US |
| dc.date.accessioned | 2019-05-16T20:28:05Z | en_US |
| dc.date.available | 2019-05-16T20:28:05Z | en_US |
| dc.date.created | 2017-08 | en_US |
| dc.date.issued | 2017-11-28 | en_US |
| dc.date.submitted | August 2017 | en_US |
| dc.date.updated | 2019-05-16T20:28:05Z | en_US |
| dc.description.abstract | Anaerobic oxidation of methane (AOM) likely represents a globally important process impacting chemical cycling of C and S across Earth’s surface. Although ubiquitous along continental margins, AOM remains underappreciated, as clear from its absence in most models for global C and S cycling. To some degree, this is because of longstanding ideas regarding the decomposition of particulate organic carbon, which assume organoclastic sulfate reduction (OSR) is the engine of carbon oxidation. Perhaps, more importantly, many sites purportedly dominated by AOM lack high-resolution pore water data, a full suite of pertinent sedimentary analyses, or both. Here, we collect and describe published seafloor organic carbon data, identify more than 400 locations with AOM in shallow sediments globally, and measure dissolved and solid concentrations of phases containing C and S at three locations to test whether AOM can drive most mass fluxes of these elements. The sites, located on slopes east of Peru and west of Japan, are under different oceanographic conditions and at different water depths (330-5086 m), but display commonalities in pore water profiles consistent with AOM. Dissolved SO42-, HS-, Ca2+, Mg2+, and Sr2+ fluxes display strong inflections at the sulfate-methane transition (SMT), while dissolved Mn2+ and Fe2+, though strongly correlated, are little affected at the SMT. Solid sulfides and perhaps S-bound organic carbon begin precipitating within 0.1 m below the seafloor (mbsf), culminating in sediment S contents of 1.18 wt. %. By contrast, authigenic carbonates begin to precipitate about 2 mbsf. Calculated sulfur mass accumulation rates (1200-4400 mol S m-2 ky-1), and authigenic carbonate precipitation rates (7.1-12.0 mol CaCO3 m-2 ky-1) are comparable to OSR published values. Inverse modeling of pore water profiles produce depth profiles with SMTs between 6.3 and 9.6 m thick, conversion of Ca2+, Mg2+, Sr2+ from solute to solid, and C and S mass balance. Additionally, modeled Fe-AOM and Mn-AOM rates are at least three orders of magnitude less than SO42-. These results show that AOM removes similar amounts of C and S from the ocean as OSR. Globally, we find AOM occurs on all continental margins at water depths up to 5500 m, indicating high CH4 flux is a common occurrence in today’s ocean. If this has also been the case in the geologic past, elemental flux models of Earth’s history may need to be revisited. | en_US |
| dc.format.mimetype | application/pdf | en_US |
| dc.identifier.citation | Miller, Clint Matthew. "Marine Carbon and Sulfur Geochemical Cycling: Reassessing Sulfate Reduction and Anaerobic Oxidation of Methane." (2017) Diss., Rice University. <a href="https://hdl.handle.net/1911/105519">https://hdl.handle.net/1911/105519</a>. | en_US |
| dc.identifier.uri | https://hdl.handle.net/1911/105519 | en_US |
| dc.language.iso | eng | en_US |
| dc.rights | Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder. | en_US |
| dc.subject | Anaerobic oxidation of methane | en_US |
| dc.subject | barium | en_US |
| dc.subject | carbon | en_US |
| dc.subject | methane | en_US |
| dc.subject | organic carbon | en_US |
| dc.subject | organoclastic sulfate reduction | en_US |
| dc.subject | sulfate | en_US |
| dc.title | Marine Carbon and Sulfur Geochemical Cycling: Reassessing Sulfate Reduction and Anaerobic Oxidation of Methane | en_US |
| dc.type | Thesis | en_US |
| dc.type.material | Text | en_US |
| thesis.degree.department | Earth Science | en_US |
| thesis.degree.discipline | Natural Sciences | en_US |
| thesis.degree.grantor | Rice University | en_US |
| thesis.degree.level | Doctoral | en_US |
| thesis.degree.major | Geochemistry | en_US |
| thesis.degree.name | Doctor of Philosophy | en_US |
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