科研之友
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摘要
Methane (CH(4)) is the second most important anthropogenic greenhouse gas in the atmosphere. Rapid variations of the CH(4) concentration, as frequently registered, 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 methane primarily associated with the presence of wetlands. In order to determine the exact time evolution of such fast concentration changes, CH(4) measurements of the highest resoution in the ice core archive are required. Here,we present a new, semicontinuous and field-deployable CH(4) detection method, which was incorporated in a continuous flow analysis (CFA) system. In CFA, samples cut along the axis of an ice core are melted at a melt speed of typically 3.5 cm/min. The air from bubbles in the ice core is extracted continuously from the meltwater and forwarded to a gas chromatograph (GC) for high-resolution CH(4) Measurements, The GC performs a measurement every 3.5 min, hence, a depth resolution of 15 cm is achieved at the chosen melt rate. An even higher resolution is not necessary due to the low pass filtering of air in ice cores caused by the slow bubble enclosure process and the diffusion of air in firn. Reproducibility of the new method is 3%, thus, for a typical CH(4) concentration of 500 ppb during an ice age, this corresponds to an absolute precision of 15 ppb, comparable to traditional analyses on discrete samples. Results of CFA-CH(4) measurements on the ice core from Talos Dome (Antarctica) illustrate the much higher temporal resolution of our method compared with established melt-refreeze CH(4) measurements and demonstrate the feasibility of the new method.
- 出版日期2009-7-15
- 单位British Antarctic Survey
