Age determination, uranium, carbon and oxygen isotopes ratios of a stalagmite of the Villars cave

The signature of Dansgaard-Oeschger events - millennial-scale abrupt climate oscillations during the last glacial period - is well established in ice cores and marine records (Labeyrie, 2000, doi:10.1126/science.290.5498.1905; Blunier and Brook, 2001, doi:10.1126/science.291.5501.109: Bond et al., 2001, doi:10.1126/science.1065680). But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of 14C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using 234U/230Th ratios. We find rapid climate oscillations coincident with the established Dansgaard-Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel (Bar-Mathews et al., 2000, doi:10.1016/S0009-2541(99)00232-6), and deep-sea records (Bond et al., 1993, doi:10.1038/365143a0; Shackleton and Hall, 2001, doi:10.1029/2000PA000513), indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 +/-0.6 and 67.4 0.9 kyr ago.

Dansgaard-Oeschger 事件（Dansgaard-Oeschger events）的特征——末次冰期内的千年尺度突发性气候振荡——已在冰芯与海洋沉积记录中得到充分确立（Labeyrie, 2000, doi:10.1126/science.290.5498.1905; Blunier and Brook, 2001, doi:10.1126/science.291.5501.109; Bond et al., 2001, doi:10.1126/science.1065680）。但此类事件在陆相环境中的影响尚不明确，且其绝对年代学在14C测年（14C dating）界限之外，以及分别超出海洋沉积记录与冰芯的年纹层计数边界时，仍存在不确定性。本文报道了采自法国西南部一处石笋的碳、氧同位素记录，该石笋已通过234U/230Th比值法获得精确定年。我们在83000至32000年前的两条同位素记录中均发现了与已确立的Dansgaard-Oeschger事件相吻合的快速气候振荡信号。该氧同位素信号与以色列Soreq洞穴的相关记录（Bar-Mathews et al., 2000, doi:10.1016/S0009-2541(99)00232-6）以及深海沉积记录（Bond et al., 1993, doi:10.1038/365143a0; Shackleton and Hall, 2001, doi:10.1029/2000PA000513）高度相似，表明此次气候振荡具有广泛的空间尺度。碳同位素信号则为西欧地区——人类文化演化的关键区域——发生剧烈且快速的植被变化提供了直接证据。我们还在法国西南部发现了距今61.2±0.6至67.4±0.9千年的一段极端寒冷气候长期阶段的相关证据。