古土壤中胡敏酸和胡敏素^(14)C测年值统计分析

STATISTICS ANALYSIS ON THE ^(14)C AGE OF HUMIC ACID AND HUMIN IN PALEOSOL

文中使用统计方法对44个不同气候条件下形成的古土壤中胡敏酸、胡敏素的14C测年结果进行分析,探讨不同组分14C年龄的可靠性。对比和统计分析结果表明,从总体上胡敏素可能是古土壤中最古老的惰性组分,其14C年龄可代表古土壤形成(平均)年龄;形成于晚更新世的地质样品胡敏酸与胡敏素的14C年龄差异并不明显,但全新世尤其晚全新世的沉积物中胡敏酸与胡敏素的14C年龄差异比较显著,可能因埋藏较浅而受到更多的污染影响;对全新世(尤其晚全新世)古土壤样品开展不同组分14C测年是保证地质事件年龄准确可靠的有效手段。

Based on 44 ^14C dates of humic acids and humins under different weather conditions, a statistics analysis was made to estimate their performance in paleosols. The following suggestions are reached： （1） A normal distribution analysis for HA/HM values deduced from 44 ^14C dates results in average value of 0.98 with standard deviation of 0.20. This seems that the humin may be the oldest fraction of soil and its ^14C age can represent the age of the paleosol. （2） The relationship between HA/HM value and the age of paleosol samples shows that the ages of humic acid and humin are indistinguishable for samples deposited in late Quaternary, but are obviously different from paleosol samples in Holocene. Their different behaviors in late Quaternary and Holocene may be related to the pollutant due to Holocene soil exposed to the surface and easily influenced by pollutant. Therefore it is suggested to use the different fractions for Holocene soil to obtain reliable radiocarbon ages for soil samples. （3） Assuming that the modern carbon pollutant entered into soil one-off, the amount of modern carbon into original carbon is estimated to be about 1.49% for late Quaternary soil sample, but this value increases to 21.37% in Holocene soil. Therefore, the amount of pollutant for Holocene soil is over 15 times than that for late Quaternary soil. If such pollutant continues to enter into soil with similar quantity during deposition, the impact percentages are 5.71% and 30.46% for late Quaternary and Holocene soil samples, respectively. The amount of modern carbon by continuously entering into soil is 2.6 times that of the one-off entering into soil for one sample in the same condition. It is further needed to state that which fractions could obtain more reliable ages for soil samples still depends on other factors such as geomorphic location, climatic zone, and soil type.