黄土中氮化物及其氮同位素对古气候变化的记录

Paleo-fertility (Corg, N, P, K) have been researched in detail in the Luochuan loess section (S0-L1-S1) since the last intergacial period. Theses results indicate that individual element of paleofertility not only responds to but also denotes change of paleo-climate and paleo-environment .Main results are generalized as follows:.l.Corg and Norg: Distributions of Corg and Norg are similar to the change of magnetic susceptibility, being matched to marine oxygen-isotope records (SPECMAPd18O ). There were slightly different between distributions of Corg and Norg in Luochuan section, which is reflected by the result that C/N ratio distribution could obviously indicate two weak weathering and pedogenesis events in Malan Loess. Correlation between Corg and Norg revealed biodiversity of vegetation, Ecosystem is vegetation gradually growed up changed from hungriness to grassland to forest in paleosoils; Ecosystem is a furthest simple hungriness in dry and cold period during interglacial rank in Malan loess, and additionally grassland for a short time during interglacial rank. But there is complicatedly evolving process for the ecosystem during early glacial rank and last glacial rank..l.Fixed NH4+: Fixed NH4+ content is relatively steady. There is good correlation between Fixed NH4+content and clay fractions(<2mm) content. At the same time Fixed NH4+ abundant was calculated according to content of caly fraction each unit(16.67′10-6); Fixed NH4+ content has better correlation with clay fraction content, but decreasing of Fixed NH4+ content in clay fraction each unit(14.17′10-6) indicates Fixed NH4+ lost to certain degree because stucture of main occurring minerals - illite-has been partly destroyed with strengthening of weathering-pedogenesis..l.Phosphorus: Changes of Porg and Pinorg are great different in Loess-Paleosoil sequences, and could quantificationally denote paleocliamte condition,（1）Pinorg content is greatly steady in Malan loess, and Pinorg abundant in source material-dust was calculated about 504.7′10-6. （2）In paleosoil, there existed a relatively furthest warm and humid climate period in which change of Pinorg could quantificationally denote climate condition by two indicators: One is the most loss rate of Pinorg designating intensity of warm and humid cliamte, in S0 layer and in S1 layer was 0.136 and 0.353 respectively；The other is time intervals of the most Pinorg loss rate designating duration of the most warm and humid climate. The most warm and humid climate duration was a very short time in S0 layer, but the most warm and humid climate continued for about 0.02Ma in S1 layer.（3）Distribution of Porg is very similar to that of the <7.8mm fraction in Malan loess, and average content of Porg has good correlation with the <7.8mm fraction in each phrase. These results indicates that Porg in loess basically inherited Porg in dust. Porg in paleosoil totally lost owing to mineralizing and leaching of Porg. During the S1 period that the most warm and humid climate continued for 0.02Ma, Porg has evolved to a balance state, and Porg/Pinorg ratio wandered at approximately 0.38.（4）According to different evolution of Porg and Pinorg, a new proxy- Porg/Pinorg, reflecting paleoclimate conditions, has been established. The Porg/Pinorg ratio is consistent with magnetic susceptibility in Luochuan loess section, and could match well to marine oxygen-isotope records, reflecting intensity of summer monsoon..l.Potassium, Ktot, Kmineral, K slow release, and K available do not seem to respond to paleoclimate change. But K available change characteristically near L1/S1, which probably implies that a tundra had been occured near L1/S1.

本项目拟通过对更新世陕西的典型黄土剖面中的氮化物分布和氮同位素进行研究，阐明氮化物和氮同位素对环境气候变化特别是灾变性气候变化的批示作用；其中对黄土氮化物的研究，可弥补过去对黄土古“肥力”研究的不足，增加对黄土高奈植被生产力和黄土来源情况的了解；氮同位素的研究，可填补国际上对黄土研究的空白，为黄土研究提供新的示踪标型。