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Large variations of C-13 values in stalagmites from southeastern China during historical times: implications for anthropogenic deforestation

机译:历史时期中国东南部石笋中C-13值的巨大变化:对人为砍伐森林的影响

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Variations in speleothem C-13 values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined C-13 variations in two stalagmites growing for the last 2200 years in Shennong Cave, Jiangxi Province, SE China. The two C-13 records corroborate well one another and show a prominent 6 parts per thousand enrichment of the C-13 values from AD 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between O-18 and C-13 values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between Mg/Ca and Sr/Ca ratios and divergent changes between C-13 values and Mg/Ca and Sr/Ca ratios from AD 700 to 1100 reveal that the prior calcite precipitation (PCP) and water-rock interaction did not dominate the increase of C-13 values. It is plausible that the obvious C-13 variation was largely influenced by the changes in vegetation cover overlying the cave. Our C-13 results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to AD 700, small fluctuations in relatively light C-13 values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during AD 700-1100, the drastic increase in C-13 values indicates persistent and massive deforestation associated with large-scale immigration into northern Jiangxi after the Rebellion of An & Shi (AD 755-763) in the Tang Dynasty and the subsequent development of agriculture and economic activity; and (iii) since AD 1100, fluctuations in relatively high C-13 values suggest that local vegetation during the last millennium has been sparse. Since the Rebellion of An & Shi, southeastern China was progressively developed, coincident with deforestation and vegetation deterioration caused by human disturbance in the form of deforestation and cultivation.
机译:鞘脂C-13值的变化可以反映上覆地表植被的变化,在历史时间尺度上,这可能代表人类活动的影响。在这里,我们研究了中国江西省神农洞最近2200年生长的两个石笋中C-13的变化。两条C-13记录相互证实,并显示了公元700年至1100年C-13值的千分之六的富集。现代方解石的同位素平衡以及O-18和C-13值之间的负相关生长轴表明动力学分级的影响可以忽略不计。 Mg / Ca和Sr / Ca比值之间的各种相关性以及公元700年至1100年C-13值与Mg / Ca和Sr / Ca比值之间的发散变化表明,先前的方解石沉淀(PCP)和水-岩相互作用并不占主导地位C-13值的增加。显然,C-13的明显变化很大程度上受洞穴上覆植被的变化影响。我们的C-13结果以及历史文献记录中的气候和人类活动记录表明:(i)在公元700年之前,相对较轻的C-13值的小幅波动反映出洞穴上方茂密的森林覆盖率,这几乎没有受到人类活动的干扰; (ii)在公元700-1100年期间,C-13值的急剧上升表明在唐代安祖氏叛乱(公元755-763年)和大韩民国叛乱后,大规模移民到江西北部造成了持续的大规模森林砍伐。农业和经济活动的后续发展; (iii)自公元1100年以来,较高的C-13值出现波动,表明最近一千年中当地植被稀疏。自从安安之乱起,中国东南部就逐渐发展起来,与森林砍伐和耕种形式的人为干扰引起的森林砍伐和植被恶化同时发生。

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