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土壤环境中广泛存在的支链甘油二烷基甘油四醚脂化合物(br GDGTs),为古气候与古环境重建研究提供了新的指标.br GDGTs的甲基化指数与环化指数分别用MBT和CBT表示,被认为主要受到年平均大气温度(MAAT)和土壤p H的控制.然而在综合不同环境样品的条件下,br GDGTs指标重建的温度和土壤p H与真实值之间存在着较大的偏差.本文报道了分别代表湿润气候(西双版纳、广州、上海)、半干旱气候(东营)以及干旱气候(兰州、青藏高原)环境下超过300个土壤样品中br GDGTs化合物随中国气候带的变化特征.总体数据表明,在湿润与非碱性环境下MBT/CBT指标重建的温度与真实温度的吻合比干旱/半干旱(MAP<500mm/a)及碱性环境下(p H>7.0~7.5)表现得更好.同样地,CBT指标在湿润与非碱性环境中可以较好地反映土壤p H的变化.与此相反的是,在干旱/半干旱与碱性环境下,CBT指标与p H之间趋于正相关关系.本文的结果表明了土壤p H、年均大气温度及降水量是控制br GDGTs在不同气候带分布的主要环境因素,并且土壤电导率、总有机碳、总有机氮与含水率在区域环境中同样起着重要作用.通过在CBT指标计算中去除br GDGT-II化合物得到了一个新的CBT指标.该指标可以提供更准确的p H估算,特别是在干旱/半干旱与碱性环境下.本文大量的中国土壤数据表明br GDGTs指标恢复的陆地大气温度与真实值之间可能存在较大偏差,因此在应用这一指标重建古气候或古环境时应相当谨慎.
Br GDGTs, which are widely existed in soil environment, provide a new index for palaeoclimate and palaeoenvironment reconstruction.br The methylation index and cyclization index of GDGTs were respectively calculated by MBT And CBT indicate that they are mainly controlled by the annual mean atmospheric temperature (MAAT) and the soil pH, however, there is a significant difference between the temperature at which the GDGTs index is reconstructed and the soil p H and the actual values under different environmental samples In this paper, we report the distribution of br GDGTs compounds in more than 300 soil samples under wet climate (Xishuangbanna, Guangzhou, Shanghai), semi-arid climate (Dongying) and arid climate (Lanzhou, Qinghai-Tibetan Plateau) The characteristics of the MBT / CBT index in wet and non-alkaline environments were consistent with the true temperature (MAP <500mm / a) and alkaline conditions (p H> 7.0 ~ 7.5). Similarly, the CBT index can better reflect the changes of p H in soils under both wet and non-alkaline conditions.Contrary to this, in the arid / semi-arid and alkaline environments, the CBT index Tends to be positively correlated with p H The results of this paper show that soil p H, mean annual temperature and precipitation are the main environmental factors controlling the distribution of br GDGTs in different climatic zones, and that the soil electrical conductivity, total organic carbon, total organic nitrogen and water content in the regional environment Also plays an important role in the removal of br GDGT-II compounds in the calculation of CBT index to obtain a new CBT index, which can provide more accurate p H estimation, especially in arid / semi-arid and alkaline environments The large amount of Chinese soil data in this paper indicates that there may be a large deviation between the terrestrial temperature and the true value of the restoration of the GDGTT indicator, so caution should be exercised when applying this indicator to reconstruct paleoclimate or paleoenvironment.