WANG Ning-Lian, YAO Tan-Dong, L. G. THOMPSON
Nitrate(NO3-) in precipitation comes from various sources, which cause many difficulties in understanding its environmental implication. Nevertheless, study of the major sources of NO3- in an ice core can not only recognize its environmental implication, but also interpret its secular variation. By analyses, it is found that solar activity, oxidation of nitrous oxide in the stratosphere and continental air mass (mainly including crustal dust and content of soluble materials in vapour in air mass) are the major sources of NO3- in the Guliya ice core. Spectral analysis of the variation of NO3- concentration in the recent 1 500 years shows strong periodicities of 23.3 a, 88.1 a, 30 a, 5.5 a and 10.4 a. Nearly all the periodicities are close to or consistent with solar activity periodicities of 22 a, 80~100 a, 5~6 a and 11 a, except the periodicity at 30 a, which is close to the periodicity of water level variations of lakes in the central Asia, about 31~34 a. Solar activity is a major factor in controlling the variation of NO3- concentration in the ice core. The secular variation of solar activity and NO3- concentration show a remarkable positive correlationship. The Maunder Minimum, Sporer Minimum, Medieval Maximum and Medieval Minimum of solar activity can be seen obviously in the curve of the variation of NO3- concentration in the Guliya ice core in the recent 1 500 years. By cross spectral analysis, it is found that there is a phase lag, about 1.5 a, between the variation of NO3- concentration in the ice core and solar activity at the periodicity of 11 a, and the variation of sunspot numbers are in advance.