黄土碳酸盐碳同位素环境意义讨论

Disscussion on Environmental Implications of Carbon Isotope of Carbonate in Loess

中文关键词:  碳酸盐  碳同位素  钙结核  黄土  古土壤  环境意义

英文关键词:Carbonate  Carbon isotope Composition  Calcium nodule  Loess-paleosol  Environmental implication

中文摘要:

      黄土碳酸盐碳同位素广泛应用于第四纪气候环境变化的研究中,以往研究中多利用钙结核、次生碳酸盐或成壤碳酸盐,认为其反映了C₄植物的丰度。黄土高原碳酸盐碳同位素表现为黄土层高,古土壤层中低,即黄土层中C₄植物丰度高于古土壤层。然而,这样的结果和黄土有机碳同位素得到的结果矛盾,有机碳同位素的结果表明温度对C₄植物的分布起到了决定性作用。由于有机碳同位素对植物类型的反映更为直接而可靠,因此碳酸盐碳同位素反映C₄植物丰度存在疑问。对黄土高原黄土碳酸盐碳同位素的系统概括后认为,第四纪期间黄土碳酸盐碳同位素与C₄植物有直接联系,但C₄植物丰度不是唯一决定性的因素,碳酸盐碳同位素的指示意义存在复杂性。在黄土高原地区,植被发育程度、与大气CO₂交换程度、植被本身的碳同位素值的变化以及原生碳酸盐的影响等因素都会对碳酸盐碳同位素产生影响。由黄土碳酸盐碳同位素的讨论可延伸到不同土壤碳酸盐碳同位素揭示的环境指示意义,不同的土壤环境,其气候条件、植被类型及发育程度、大气CO₂的交换情况、微生物的活动及土壤次生碳酸盐受原生碳酸盐溶解的影响等因素都会对碳同位素产生不同程度影响,哪种或哪几种因素产生主要作用,在不同区域土壤环境中是不一样的。具体研究中需确定影响的核心因素,才能确定碳同位素的环境指示意义。

英文摘要:

      Carbon isotopic composition of carbonate in Loess is widely applied in researches on Quaternary climatic-environmental change.Carbon isotopic composition,whatever in calcium nodule,secondary carbonate or pedogenic carbonate,reflects C₄ plant abundance in most researches on past climate change.In Loess Plateau,the carbon isotopic composition of carbonate is high in loess and low in paleosol,which means C₄ plant abundance is higher in loess than that in paleosol.However,this result contradicts with the result from organic carbon isotopic composition in loess.The result of organic carbon isotopic composition in Loess shows that temperature is decisive on the distribution of C₄ plant.As the organic carbon isotopic composition reflects plant type much directly and reliably,it becomes doubt that the carbon isotopic composition of carbonate reflects the abundance of C₄ plant.Based on systematically generalizing carbon isotopic compositions of carbonate in Loess Plateau,we believe that the carbon isotopic composition of carbonate in Loess Plateau during Quaternary is related to C₄ plant,but it is not the only and decisive factor.The implication of carbon isotopic composition of carbonate in loess is very complicated.On Loess Plateau,the degree of vegetation development,the exchange degree of soil CO₂ with CO₂ in atmosphere,the change of carbon isotopic composition of vegetation itself and impact of primary carbonate,all these factors will affect the carbon isotopic compositions of carbonate in loess.Thus we can conclude that in different soil environment,such as climatic conditions,vegetation type and degree of vegetation development,soil CO₂ exchange with atmospheric CO₂,microbial activity and the effect of dissolution of primary carbonate,have impacted on carbon isotopic composition of carbonate.In different climatic region,which factors is more important in soil environment is not the same.It needs to make sure the dicisive factor on carbon isotopic composition of carbonate,then one can understand the implications of carbon isotopic composition.