华县老官台全新世黄土剖面pH值及其古气候意义研究

pH value′s measurement and research of its palaeoclimatic meaning in the Holocene loess section

对华县老官台剖面190个样品的土壤pH值测定表明:pH值的变化从总体上与其他代用指标对应良好,可用于古气候环境的研究.当气候变得湿润时,植被生长茂盛,生物化学风化强烈,土壤pH值低;当气候变干冷时,植被稀疏,生物化学风化微弱,土壤pH值高.但就局部层位的对比情况看其pH值存在差异,主要表现在气候转型期的突变方面(不像其它指标的渐变),其两个低谷均突然出现在古土壤层S20和S10的中部,这两个古土壤层上部和下部又突然转为峰值.pH值的上述变化特点似乎说明其对降水的变化更加敏感,从这个意义上讲,pH值的变化是一个很好地反映降水情况非常敏感的气候代用指标,其可以用来定量恢复古气候中的降水量的多少,具体的实施方案还有待于进一步研究.

By measuring and analyzing of pH values of 190 samples of Laoguantai loess section in Hua county,it shows that the changes of pH values corresponds well with the change of other climatic proxy indexes and so it can be used to study palaeoclimate. The pH value is lower when climate is warmer and moister because of luxuriant growth of vegetation and intensity weathering of biochemistry, while climate is colder and drier the pH value is higher because of poor growth of vegetation and faint weathering of biochemistry. In addition, There exist differences in some layers between the curves of pH value and the other climatic proxy indexes, which mainly displays in the abrupt change during climatic transformation periods(do not like gradual change of the other proxy indexes)that its low valleys abruptly appear in the middle position of S^2_0 soil and S^1_0 soil, in up and down section nearby it abruptly transform peak values. Such changes of pH value seemly indicates its changes more sensibility to change of precipitation, which shows the change of the pH value is a good proxy index indicating precipitation condition and it can be used to determine precipitation quantitatively.