Laschamp地磁场漂移事件发生的确切年代(~42 ka BP)已通过相对独立的同位素定年手段确定,并被证实具有全球性特征。但这一事件在我国马兰黄土地层中的记录存在着明显的空间差异。本文初步对比了最近发表的黄土高原洛川剖面^(10)Be记录的Laschamp漂移信息和前人根据该剖面古地磁参数异常结合Heinrich冷事件所确定的Laschamp记录层位结果,进一步证实了这一地磁漂移事件在马兰黄土地层中记录的真实性.同时初步对比也显示根据旧Be产率异常增高对应的磁场强度低值确定的Lashcamp层位偏上,而古地磁异常确定的Laschamp层位相对偏下约76 cm。排除因采样剖面分辨率不同的可能影响,两种手段记录同一地磁漂移事件的显著层位差异具有指示意义,可能为未来研究黄土-古土壤序列沉积剩磁获得过程提供新的途径。
A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River,Shanxi Province,China.Based on the tree-ring-width indices,a 157-year long Palmer Drought Severity Index(PDSI) was reconstructed,which explains 53.7% of the variance of the modeled PDSI over the common period 1957-2008.The drought periods in the study area include 1914-1931 and 1970 to the present,whereas the wet periods were 1866-1892 and 1932-1969.The drought of 1914-1931 was a severe long-lasting drought with a low inter-annual variability,and the drought of 1970-2009 was an overall long-term drought with a high inter-annual variability.The period of 1866-1892 is a continuously wet period with a low inter-annual variability and the period of 1932-1969 is an overall long-term wet period with a high inter-annual variability.The reconstructed PDSI series in the source of the Fenhe River shows synchronous variations with the regional drought/wetness indices.Spatial correlation analyses indicate that the higher correlations lie exclusively in the Fenhe River Basin.This indicates that the reconstructed PDSI has regional representativeness and can represent the drought history of the entire Fenhe River Basin to some extent.Furthermore,the reconstructed PDSI matches with the variability of the per unit yield of summer grain crops in Shanxi Province very well and they have significant correlation.From a long-term perspective the reconstructed PDSI series could supply scientific and valuable information to the water resources management and then help the sustainable development in agricultural production,economic development,and ecosystem balance.
