| 氧化条件对样品有机碳同位素测定的影响因素讨论 |
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| 关键词:carbon isotopes soil organic matter oxide tion condition conditional experiments |
| 基金项目:本文得到国家重点基础研究发展规划项目（编号:2004CB720200)，国家自然科学基金项目（编号:40121303,40373008)，全国优秀博士论文研究基金项目，黄土与第四纪地质国家重点实验室开放基金（编号：SKLLQG0525)等的资助。 |
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| A Discussion on the Effects of Oxidation Conditions On δ13C of Organic Matter |
| The carbon isotopic composition of organic matter in soil has been widely used in global change research and in reconstruction of paleovegetation and paleoclimate. The basic principle of organic carbon isotopic analysis lies in transforming the organic matter into CO2 under the superfluous oxygen condition at high temperature, and then separating and purifying the resultants so as to get pure CO2 for determining their δ13C.
In the study of organic carbon isotope composition,various oxidation temperatures and oxidation durations have been used, but researches about possible effects of oxidation conditions on δ13C of organic matter are very insufficient. In order to understand whether various oxidation conditions may result in organic carbon fractionation, and what the degree of possible effects of various oxidation conditions on δ13C of organic matter is, the authors selected various types of samples (standard material for organic carbon，plants, modem soil, loess, red clay, etc.）and used the tube-sealed method to oxidize samples at various oxidation temperatures: 500℃，550℃，650℃，750℃，850℃，900℃and 950℃The oxidation temperature was then kept for 2. 5 hours, and after that the muffle was cooled to room temperature with door closed.
According to the experimental results, the oxidation temperature of 850℃ and the constant temperature time of 2.5 hours are enough to assure adequate oxidation of organic matter for such sam讨es as standard material for organic carbon, plants, modern soil and younger loess, with no fluctuation of their δ13C values and no fractionation.
Nevertheless, for older loess and red clay samples at oxidation temperature of 850℃and constant temperature time of 2.5 hours, the δ13C values cannot reach constancy and still have a somewhat positive trend. This is probably attributed to strong diagenesis of older samples which might contain some carbonaceous mineral inclusions. With the increase of oxidation temperature, these carbonaccous mineral inclusions begin to break down and release CO2 gas. For these samples, 850℃ or even higher oxidation temperature cannot guarantee the stableness of δ13C values of the organic matter, and hence further experiments are necessary for determining appropriate oxidation conditions. |
| CAO Yunning,LIU Weiguo,NING Youfeng,ZHANG Qingle,WANG Zheng.2005.A Discussion on the Effects of Oxidation Conditions On δ13C of Organic Matter[J].Acta Geoscientica Sinica,26(z1):55-56. |
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