贵州黑洞4750年以来高分辨率石笋δ^(13)C记录

A High-Resolution Stalagmiteδ^(13)C Record for the Past 4750 Years from Dark Cave,Guizhou,SW China

【目的】全球变暖背景下,喀斯特地貌广布的西南地区可能面临石漠化加剧的风险,对该区域石漠化演变历史的重建具有重要意义。【方法】通过采自贵州省黔西县黑洞一支石笋(HD12)的29个230Th年龄和954个δ^(13)C数据,重建了该地区过去4 750年的生态环境演变历史。【结果与结论】发现在4 322~3 526 a B.P.以及803~82 a B.P.时段存在两个显著的δ^(13)C正偏移,说明这两个时段洞穴上方的生态环境出现了恶化。HD12石笋δ^(13)C记录在约803 a B.P.的显著偏正持续了约290 a,其振幅达4.2‰,指示了该区域石漠化的扩张过程。这一时期西南地区多个洞穴石笋δ^(13)C值的一致偏正特征,可能指示了宋末靖康事件(823 a B.P.)后,人口的大量迁入和气候的干旱化导致了该区域石漠化的扩张。HD12石笋δ^(13)C值在4 322~3 526 a B.P.时期的偏正,振幅达4.9‰,其中4 322~3 977 a B.P.偏正过程对应于北半球4.2 ka事件,而3 777~3 526 a B.P.的偏正对应3.7 ka事件,两个时期的干旱事件在西南地区的多个石笋与湖泊记录中均有体现,说明在此期间,亚洲夏季风减弱,降水减少可能引起了该区域植被覆盖度大幅降低和土壤严重退化。

[Objective]Global warming may increase the risk of expansion of karst rock desertification(KRD)in Southwest(SW)China,where karst landscapes are widespread,so it is important to reconstruct the evolution of KRD in this region.[Methods]In this study,the regional eco-evolution of the past 4750 years was reconstructed based on 29230Th ages and 954δ^(13)C records collected from stalagmite HD12 in Dark cave,Qianxi county,Guizhou province.[Results and Conclusions]Two significant positiveδ^(13)C offsets were found at 4322-3526 a B.P.and 803-82 a B.P.,indicating deterioration of the ecological environment at those times.A significant positiveδ^(13)C record of the HD12 stalagmite at about 803 a B.P.persisted for about 290 years with an amplitude of 4.2‰,indicating expansion of KRD in the area.The consistent positiveδ^(13)C in stalagmites from several caves in SW China during this period suggests that the large-scale population migration and climatic drought after the Jingkang event(823 a B.P.)promoted the expansion of KRD in this region.During 4322-3526 a B.P.,the positive shift of HD12 stalagmiteδ^(13)C values had an amplitude of 4.9‰.The positive shift at 4322-3977 a B.P.corresponds to the 4.2 ka event,and for 3777-3526 a B.P.it corresponds to the 3.7 ka event.These two periods of drought are also reflected in several stalagmite and lake records in SW China,suggesting that the weakened Asian summer monsoon and reduced precipitation at those times may have caused a large reduction in vegetation cover and severe soil degradation in the region.