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CHEMICAL WEATHERING ACROSS SPATIAL AND TEMPORAL SCALES:
FROM LABORATORY EXPERIMENTS TO GLOBAL MODELS
by
Mark Albert Torres
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
August 2015
Copyright 2015 Mark Albert Torres
Object Description
| Title | Chemical weathering across spatial and temporal scales: from laboratory experiments to global models |
| Author | Torres, Mark Albert |
| Author email | marktorr@usc.edu;markt253@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2015-05-26 |
| Date submitted | 2015-07-29 |
| Date approved | 2015-07-30 |
| Restricted until | 2015-07-30 |
| Date published | 2015-07-30 |
| Advisor (committee chair) | West, A. Joshua |
| Advisor (committee member) |
Amend, Jan Fischer, Woodward |
| Abstract | When exposed at Earth’s surface, rocks are out of thermodynamic equilibrium with respect to their environment. This disequilibrium drives the chemical transformation, or weathering, of these rocks into soils and governs the chemical composition of natural waters and the atmosphere. Over geologic timescales, complex feedbacks associated with weathering processes are presumed to regulate the concentrations of CO₂ and O₂ in the atmosphere with profound implications for the habitability of the planet. However, a mechanistic understanding of how biologic, tectonic, and climatic conditions interact to control weathering fluxes has remained elusive. In part, our understanding of weathering processes is hindered by the fact that they operate continuously over an enormous range of spatial (atomic to global) and temporal (microseconds to millions of years) scales, but we can only make measurements over discrete ranges of these values. While each scale of observation available offers unique insights, it is often difficult to link observations made at different scales. For my Ph.D., I focused on three distinct projects that span the range of observable scales in order to better understand the links between chemical weathering and long-term biogeochemical cycles. ❧ Chapter 2: Laboratory insights into microbial mineral dissolution. Rocks and minerals represent a major reservoir of bio-essential nutrients. While abundant, some of these lithogenic nutrients, like iron, are not readily bio-available. As a result, many organisms produce metal-binding ligands to scavenge these trace nutrients from the environment. Using targeted laboratory experiments with live microbial cultures and purified microbial ligands, I explored efficacy by which microbes can access trace nutrients from common silicate minerals (Torres et al., in prep). In addition to providing insight into biological nutrient scavenging strategies, this work also provides the basic research necessary to develop microbe-based CO₂ sequestration techniques since the dissolution of silicate minerals for nutrient acquisition also sequesters CO₂. ❧ Chapters 3 & 4: Geomorphic control on the hydrology and carbon budget of weathering. Erosional processes and hydrology are known to influence chemical weathering rates by controlling the timescales over which minerals react. Accurately describing the complex linkages between weathering, erosion, and hydrology observed in natural environments remains a major research challenge. To help address this problem, a major part of my Ph.D. was focused on characterizing how chemical weathering and hydrology are coupled in distinct erosional environments. This work combines hydrologic monitoring, solute chemistry, and water isotope analyses in order to robustly document how water is stored in catchments and link this to measured solute fluxes from chemical weathering (Clark et al., 2014; Torres et al., 2015). The results of this study are intriguing in that the hydrological control of weathering was found to vary predictably with the erosional regime, which has important implications for how changes in tectonic activity affect global weathering fluxes. ❧ By affecting the timescales over which weathering reactions occur, erosional processes also influence which minerals react due to the intrinsic variability in the reaction rates of different minerals. Rapid erosion rates favor the oxidation of sulfide minerals relative to the dissolution of silicate minerals, which leads to the release of CO₂ into the ocean-atmosphere system. To trace sulfide oxidation and its effect on the carbon budget, I combined multiple isotopic systems (e.g., S, C, and Sr) with major and trace element analyses (Torres et al., in prep). By making observations in catchments with diverse erosional regimes, it was possible to interrogate how sulfide oxidation fluxes relate to erosional processes. My results showed that sulfide oxidation dominates in rapidly eroding environments and leads to the significant release of CO₂. This is in contrast to more slowly eroding environments, where CO₂ consumption during silicate weathering dominates. ❧ Chapter 5: The evolution of the Cenozoic carbon cycle. My research on sulfide oxidation in modern systems suggested a link between tectonic uplift and the carbon budget of weathering processes with important implications for the long-term carbon cycle. To test this hypothesis, I incorporated the effects of sulfide-oxidation driven CO₂ release into a model of the Cenozoic carbon cycle. The Cenozoic carbon cycle has long plagued geochemists as isotopic records suggest changes in weathering fluxes that appear to be inconsistent with the requirement of mass balance in the long-term carbon cycle. By incorporating sulfide oxidation as a CO₂ source, I was able to provide a novel solution to the "Cenozoic isotope-weathering paradox" (Torres et al., 2014). |
| Keyword | weathering; rivers; olivine; pyrite; silicate |
| Language | English |
| Format (imt) | application/pdf |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Torres, Mark Albert |
| Physical access | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-TorresMark-3763.pdf |
| Archival file | Volume4/etd-TorresMark-3763.pdf |
Description
| Title | Page 1 |
| Repository email | cisadmin@lib.usc.edu |
| Full text | CHEMICAL WEATHERING ACROSS SPATIAL AND TEMPORAL SCALES: FROM LABORATORY EXPERIMENTS TO GLOBAL MODELS by Mark Albert Torres A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (GEOLOGICAL SCIENCES) August 2015 Copyright 2015 Mark Albert Torres |
