干旱化对成土碳酸盐碳同位素组成的影响

土壤碳酸盐的碳同位素组成可以作为古环境变化的指标.本文对黄土高原地区S1以来成土碳酸盐和红粘土中碳酸盐的碳同位素进行了研究.根据渭南、吉县、长武和会宁4个剖面末次间冰期以来土壤碳酸盐的碳同位素分析结果,探讨了不同气候条件下成土碳酸盐碳同位素组成的特征及其环境意义,指出气候的干湿程度可能是影响黄土地区成土碳酸盐δ13C值的主要原因;西峰红粘土序列碳酸盐的碳同位素记录表明,δ13C值在4.0Ma B.P.前后有一个明显增加的趋势,反映了我国西北地区上新世干旱化的发展,可能与青藏高原在这一时期发生较大规模的隆升有关.

Aridification and its influence on carbon isotope composition of pedogenic carbonate

Yunnan Guizhou Plateau,the middle tier on the eastern slope of Qinghai Xizang Plateau,is a complex geomorphic unit with a large altitude gradient in the South Asia. Impacts of the Qinghai Xizang uplift on the modern environment in the area mainly embody:(1) barrier effect of global atmospheric pollutants and detaining effect of local atmospheric pollutants;(2) enhancement of regional chemical weathering and altitude related effect of physical weathering;(3) low latitude and high altitude effect of environmental geochemical process of surface earth. Lake sediments embrace materials originating not only from watershed but also from atmospheric deposition. 137 Cs is an excellent tracer for watershed erosion and lake deposition. 7 Be is an ideal tracer for seasonally transportation of environmental particles. Differentials of 7 Be/ 137 Cs in the top soils between western Yunnan and central Guizhou show different characteristics of 137 Cs and 7 Be deposition accumulation in the two regions. 7 Be inventories in the sediments of Erhai Lake correspond to that in the soils of its watershed in the western Yunnan. 7 Be inventories in sediments of Hongfeng Lake are much higher than the average value in the soil profiles of its watershed. 137 Cs inventories in sediments of Hongfeng Lake is 7.1 times of the Erhai Lake. The model analysis indicated that 7 Be atmospheric deposition in western Yunnan was similar to central Guizhou. Prior to 1986, 137 Cs inventories from atmospheric fallout in the western Yunnan and the central Guizhou were (0.11±0.01) Bq/cm 2 and (0.37± 0.01 ) Bq/cm 2,respectively. This indicates that fallout 137 Cs in the western Yunnan was much lower than that in the central Guizhou. The regional differentials of the 137 Cs fallout reflect that the uplift of Qinghai Xizang Plateau would have a barrier effect on the precipitation of global atmospheric pollutants in the western Yunnan.