Development of a method for continuous flow analysis of methane and its application to polar ice cores

Schüpbach, Simon (2010). Development of a method for continuous flow analysis of methane and its application to polar ice cores (Unpublished). (Dissertation, Universität Bern, Philosophisch–naturwissenschaftliche Fakultät, Physikalisches Institut, Abteilung für Klima– und Umweltphysik)

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Polar ice cores represent a major archive in paleoclimatology, providing a wide spectrum of information about past climate and in particular about the composition of the atmosphere as far back as 800 000 years. For a better interpretation of this valuable archive an exact synchronization of the time scales of different ice cores from various sites in Greenland and Antarctica is crucial. Rapid variations of the methane (CH4) concentration, as frequently occurring, for example, during the last ice age, have been used as reliable time markers for the definition of a common time scale of polar ice cores. In addition, these variations indicate changes in the sources of CH4 primarily associated with the presence of wetlands.
Established methods for measuring CH4 concentrations on discrete samples of air enclosed in ice cores have provided reliable records of one of the most important greenhouse gases in the atmosphere. In order to determine the exact time evolution of fast concentration changes, CH4 measurements of the highest resolution in ice cores are required.
During this PhD thesis a novel, semi-continuous CH4 detection method was developed, which is incorporated in a well-established continuous flow analysis (CFA) system traditionally used for analyses of aerosol constituents in ice cores. The air is extracted continuously from the melt water flow by using a gas-permeable hydrophobic membrane. Subsequently the gas is analyzed by regular injections of gas samples into a gas chromatograph providing a semi-continuous CH4 record with a typical depth resolution of 15 cm.
Measurements using the new high-resolution method on the Antarctic TALDICE ice core provided a CH4 record in unprecedented resolution back to the penultimate glacial period. The new data are used for refining the age scale of the TALDICE ice core based on CH4 synchronization with the Antarctic EPICA Dome C ice core, significantly reducing the uncertainty of the age scale in the discussed interval.
For measurements on the Greenland NEEM ice core, the CFA system, including the new CH4 method, was shipped to the NEEM camp. As a result of these measurements, the first continuous CH4 record of a Greenland ice core covering the entire last glacial period was produced.
In response to the successful continuous air extraction established within this thesis, two additional devices based on laser absorption spectroscopy have been connected to the CFA system to measure CH4 continuously on the NEEM ice core. First results of these measurements show that while synchronization of the NEEM ice core is possible with all three CH4 records, the records obtained with the novel laser spectroscopy devices have the potential to provide new information regarding the dynamics of atmospheric CH4 concentrations at very short time scales and of low amplitudes due to their even higher resolution and precision.
In parallel to the CH4 measurements continuous aerosol chemical records have been obtained using the CFA providing information of aerosol concentration changes from both polar regions over the last glacial cycle.

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