Abstract

The results of studying stable carbon isotopes of the organic matter of Late Pleistocene and Holocene soils of the Baikal region are presented. The δ¹³С values in soils of different ages varies from –30.00 to –21.36‰, which indicates the formation of their organic matter from C3 plants at least in the past 35 ka. Fractionation of isotopes during the organic matter mineralization leads to an increase in δ¹³С values with the depth. At the same time, in soils of steppe and forest-steppe landscapes, an increase in δ¹³С is about 3‰, whereas in forest soils it can reach 4–5‰, which is most likely associated with a slow transformation of organic residues in the upper horizons of forest soils. In the Late Glacial and Early Holocene soils, an elevated content of organic carbon is noted, in which the stable carbon isotopic composition is lighter than that in the recent soils. This may be explained by the influence of permafrost slowing down the transformation of organic matter. In the sequence starting with rather dry soils of the Ol’khon region and the Selenga Mountains to the forest-steppe soils of the Upper Angara region with its more humid conditions and, further, to the taiga soils in the south of Central Siberia, there is a marked decline of δ¹³С values in the organic matter. Thus, we deal with a bright example of the δ¹³С dependence on the soil water supply, i.e., on precipitation during the growing season. Reconstruction of precipitation based on δ¹³С values attests to a gradual aridization of the climate starting from the Late Glacial period with a maximum drying in the Middle Holocene, while in the Late Holocene the level of humidization increases. A tendency towards a gradual decrease in humidity was also observed during MIS-3. It is probable that the most humid climate was during the formation of the Early Karga soils. In the range of 36–31 ka BP, climatic humidity decreased and became comparable with the modern one. At the end of MIS-3, climatic humidity was below the current level.

中文翻译：

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贝加尔湖地区晚更新世和全新世土壤有机质的稳定碳同位素组成

摘要

给出了贝加尔湖地区晚更新世和全新世土壤有机物的稳定碳同位素研究结果。的δ ¹³在不同年龄的土壤С值变化从-30.00至-21.36‰，这表明它们的有机物从C3植物至少在过去的35 KA的形成。有机物矿化导致增加δ期间同位素分馏^13个与深度С值。与此同时，在草原和森林草原景观，增加δ土壤¹³С大约为3‰，而在森林土壤中则可以达到4-5‰，这很可能与森林土壤上层有机物的缓慢转化有关。在晚冰川期和全新世早期土壤中，有机碳含量升高，其中稳定的碳同位素组成比最近的土壤轻。这可能是由于多年冻土的影响减慢了有机物的转化。首先是奥尔康地区和塞伦加山脉的相当干燥的土壤，再到潮湿条件更为潮湿的上安加拉地区的森林草原土壤，再到西伯利亚中部南部的针叶林土壤，是δ的明显下降¹³ С值中的有机物。因此，我们处理了δ的一个很好的例子¹³在生长期间土壤水分供应，即对降水С依赖。基于δ沉淀的重建^13个С值证明了从晚冰期与中全新世最大干燥开始气候的逐渐干燥化，而在晚全新世的humidization的水平增加。在MIS-3期间还观察到了湿度逐渐降低的趋势。最潮湿的气候可能是在卡尔加早期土壤形成期间。在36-31 ka BP的范围内，气候湿度下降并与现代湿度相当。在MIS-3结束时，气候湿度低于当前水平。