Soil nitrogen isotopic composition of the Xifeng loess-paleosol sequence and its potential for use as a paleoenvironmental proxy

The isotopic composition of soil nitrogen (soil delta N-15 values) has been widely used to explore the soil biogeochemical cycle and study land vegetation conditions. However, the delta N-15 values in the loess-paleosol sequence have not been thoroughly studied. In this study, we provide the first report of delta N-15 values from the Xifeng loess-paleosol profile, which spans the last 130 ka. The delta N-15 values show great variation (2.1 parts per thousand-6.1 parts per thousand) in the Xifeng loess sequence. According to these results, the delta N-15 values have a similar pattern with changes in the magnetic susceptibility (MS) and exhibit significant differences within the glacial-interglacial cycle over the last 130 ka. We hypothesize that climate conditions and land vegetation conversion could be reflected by the changes in the delta N-15 values within the glacial-interglacial cycle. (1) The delta N-15 values are positively correlated with the reconstructed mean annual temperature (MAT) and mean annual precipitation (MAP) on the glacial-interglacial time scale. Moreover, it appears that the MAT may be more effective than the MAP for the delta N-15 changes in the Xifeng loess-paleosol sequence. (2) Vegetation changing from grasses to shrubs may cause N-15 depletion during the glacial period. In addition, increasing grass groups may cause N-15 enrichment of the soil during the interglacial stage in the Xifeng loess-paleosol sequence. Because nitrogen is one of the most significant nutrient elements for vegetation, paleovegetation changes may be the main controlling factor for delta N-15 values in the loess-paleosol section. Therefore, delta N-15 values have the potential for use as a proxy in paleoenvironmental reconstructions of the Chinese Loess Plateau. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.