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Abiotic and biotic methane dynamics in relation to the origin of life
Stockholm University, Faculty of Science, Department of Geological Sciences.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Methane (CH4) plays an important role in regulating Earth’s climate. Its atmospheric concentrations are related to both biotic and abiotic processes. The biotic one can be formed either by chemoautotrophic or heterotrophic pathways by methanogens. Abiotic CH4 formation can occur from several sequential reactions starting with H2 production by serpentinization of Fe-bearing minerals followed by Fischer-Tropsch Type reactions or thermogenic reactions from hydrocarbons. In the presence of suitable electron acceptors, microbial oxidation utilizes CH4 and contributes to regulating its emission.  From the perspectives of astrobiology and Earth climate regulation, this thesis focuses on: (1) Dynamics of CH4 formation and oxidation in lake sediments (Paper I), (2) Constructing an automatic flux chamber to facilitate its emission measurements (Paper II), (3) dynamics of both abiotic and biotic CH4 formation processes related to olivine water interaction in temperature range 30 - 70°C (Paper III and IV).

Paper I showed that potential CH4 oxidation strongly correlated to in situ its formation rates across a wide variety of lake sediments. This means that the oxidation rates could be enhanced in environments having the high formation rates. Thereby, the oxidation would likely be able to keep up with potentially increasing the formation rates, as a result diffusive CH4 release from freshwater sediments might not necessarily increase due to global warming. Paper II presented a new automated approach to assess temporal variability of its aquatic fluxes. Paper III and IV together revealed that H2 can be formed via olivine-water interaction. Abiotic CH4 formation was formed likely by Fischer-Tropsch Type reactions at low inorganic carbon concentration but by thermogenic processes at high inorganic carbon concentration. Paper IV showed that biotic methanogenic metabolism could harvest H2 and produce CH4. The dynamics of these processes seemed strongly affected by carbonate chemistry.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University , 2012. , 50 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 348
Keyword [en]
methane, methanogens, methane formation, methane oxidation, lake sediment, olivine, origin of life
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-65895ISBN: 978-91-7447-428-2 (print)OAI: oai:DiVA.org:su-65895DiVA: diva2:466347
Public defence
2012-01-26, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Submitted. Available from: 2012-01-04 Created: 2011-12-15 Last updated: 2011-12-16Bibliographically approved
List of papers
1. Implications of temperature and sediment characteristics on methane formation and oxidation in lake sediments
Open this publication in new window or tab >>Implications of temperature and sediment characteristics on methane formation and oxidation in lake sediments
2010 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 100, no 1-3, 185-196 p.Article in journal (Refereed) Published
Abstract [en]

Methane emissions from aquatic environments depend on methane formation (MF) and methane oxidation (MO) rates. One important question is to what extent increased temperatures will affect the balance between MF and MO. We measured potential MF and MO rates simultaneously at 4, 10, 20 and 30A degrees C in sediment from eight different lakes representing typical boreal and northern temperate lake types. Potential MF rates ranged between 0.002 and 3.99 mu mol CH4 g(d.w.) (-1) day(-1), potential MO rates ranged from 0.01 to 0.39 CH4 g(d.w.) (-1) day(-1). The potential MF rates were sensitive to temperature and increased 10 to 100 fold over the temperature interval studied. MF also differed between lakes and was correlated to sediment water content, percent of organic material and C:N ratio. Potential MO did not depend on temperature or sediment characteristics but was instead well explained by MF rates at the in situ temperature. It implies that elevated temperatures will enhance MF rates which may cause increased methane release from sediments until MO increases as well, as a response to higher methane levels.

Keyword
Global warming, Greenhouse gas, Methane formation, Methane oxidation, Littoral sediment, Lake
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-47282 (URN)10.1007/s10533-010-9415-8 (DOI)
Available from: 2010-11-30 Created: 2010-11-30 Last updated: 2017-12-12Bibliographically approved
2. An automatic flux chamber for investigating gas flux at water – air interfaces
Open this publication in new window or tab >>An automatic flux chamber for investigating gas flux at water – air interfaces
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Aquatic ecosystems are major sources of greenhouse gases (GHG).  Representative measurements of GHG fluxes from aquatic ecosystems to the atmosphere are vital for quantitative understanding of climate related biogeochemistry. Fluxes occur at high temporal variability at diel or longer scales which are not captured by traditional short term deployments (typically on the order of 30 minutes) of floating flux chambers. High temporal frequency measurements are necessary but are extremely labor intensive if manual flux chamber based methods are used. Eddy correlation methods require expensive equipment and lead to uncertain results because of the high spatial variability of fluxes from restricted areas. Therefore we designed an inexpensive and easily mobile automatic flux chamber system (AFC) for extended deployments. This device includes a flux chamber and a box with the controller/datalogger, valves, a pump, a 12 V battery and a solar cell. Sensors tested in this study recorded CH4 concentration in the chamber headspace, temperature in the water and air and barometric pressure, but other sensors for CO2 and weather variables can also be attached to the system. The unit was designed to measure in situ accumulation of gas in the chamber and also to collect gas samples in an array of sample bottles for subsequent analysis in the laboratory, providing two independent ways of CH4 concentration measurements.  We here present the AFC design and function together with data from initial laboratory tests and from a field deployment.

National Category
Engineering and Technology
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-65894 (URN)
Available from: 2011-12-15 Created: 2011-12-15 Last updated: 2011-12-16Bibliographically approved
3. Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C
Open this publication in new window or tab >>Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C
Show others...
2011 (English)In: Geochemical Transactions, ISSN 1467-4866, E-ISSN 1467-4866, Vol. 12, no 6Article in journal (Refereed) Published
Abstract [en]

Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures   above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian   CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the   CH4 and H2 formation potential of forsteritic olivine.

The results show low temperature CH4 production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH4 source trapped in the crystal structure of the olivine showed no signs of incorporated CH4. Also, the available sources of organic carbon were not enough to support the total amount of CH4 detected in our experiments. There was also a linear relationship between silica release into solution and the net CH4 accumulation into the incubation bottle headspaces suggesting that CH4 formation under these conditions could be a qualitative indicator of olivine dissolution.

It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze   the formation of CH4, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH4 formation both on Earth and on other terrestrial bodies.

National Category
Other Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-61762 (URN)10.1186/1467-4866-12-6 (DOI)000293981700001 ()
Available from: 2011-08-29 Created: 2011-08-29 Last updated: 2017-12-08Bibliographically approved
4. The potential for abiotic methane formation fueled by olivine dissolution
Open this publication in new window or tab >>The potential for abiotic methane formation fueled by olivine dissolution
(English)In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908Article in journal (Refereed) Submitted
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-65502 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2017-12-08Bibliographically approved

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