Isotope characterisation of Villars Cave stalagmites

We present a new mid-latitude speleothem record of millennial-scale climatic variability during OIS3 from the Villars Cave that, combined with former published contemporaneous samples from the same cave, gives a coherent image of the climate variability in SW-France between ~55 ka and ~30 ka. The 0.82 m long stalagmite Vil-stm27 was dated with 26 TIMS U-Th analyses and its growth curve displays variations that are linked with the stable isotopes, both controlled by the climatic conditions. It consists in a higher resolved replicate of the previously published Vil-stm9 and Vil-stm14 stalagmites where Dansgaard-Oeschger (DO) events have been observed. The good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions, especially high resolution pollen records (ODP 976 from the Alboran Sea, Monticchio Lake record from southern Italy) and the nearby MD04-2845 Atlantic Ocean record, permits to draw a specific climatic pattern in SW-France during the OIS3 and to see regional differences between these sites. Main features of this period are: 1) warm events corresponding to Greenland Interstadials (GIS) that are characterized by low speleothem d13C, high temperate pollen percentages, warm temperatures and high humidity; among these events, GIS#12 is the most pronounced one at Villars characterized by an abrupt onset at ~46.6 ka and a duration of about 2.5 ka. The other well individualized warm event coincides with GIS#8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher d13C; 2) cold events corresponding to Greenland Stadials (GS) that are clearly characterized by high speleothem d13C, low temperate pollen abundance, low temperature and enhanced dryness, particularly well expressed during GS coinciding with Heinrich events H5 and H4. The main feature of the Villars record is a general cooling trend between the DO#12 event ~45.5 ka and the synchronous stop of the three stalagmites at ~30 ka ±1, with a first well marked climatic threshold at ~41 ka after which the growth rate and the diameter of all stalagmites slows down significantly. This climatic evolution differs from that shown at southern Mediterranean sites where this trend is not observed. […]本研究报道了一条采自维拉尔洞穴（Villars Cave）、记录了海洋同位素阶段3（OIS3）期间千年尺度气候变率的中纬度洞穴碳酸盐沉积（speleothem）新序列。结合该洞穴此前已发表的同期样品，本序列构建了约55 ka至约30 ka法国西南部地区气候变率的连贯图景。本次研究的石笋Vil-stm27总长0.82 m，通过26次热电离质谱铀钍（TIMS U-Th）测年获得年代框架，其生长曲线呈现的变化与稳定同位素特征相关，二者均受气候条件调控。该序列是此前发表的Vil-stm9与Vil-stm14石笋的高分辨率复本，其中已识别出丹斯果德-厄施格（Dansgaard-Oeschger, DO）事件。该三支石笋间的良好一致性，以及与其他古气候重建结果——尤其是高分辨率孢粉记录（阿尔沃兰海大洋钻探计划976航次（ODP 976）、意大利南部蒙蒂奇奥湖记录）与邻近海域大西洋MD04-2845岩芯记录——的对比，使得我们能够明确海洋同位素阶段3期间法国西南部的特定气候模式，并揭示各站点间的区域差异。该时期的主要特征包括：1）对应格陵兰间冰段（Greenland Interstadials, GIS）的暖期事件，其典型特征为石笋δ¹³C值偏低、温带孢粉百分含量偏高、气温升高且湿度增大；其中GIS#12是维拉尔洞穴最为显著的暖期事件，其起始时间约为46.6 ka，持续时长约2.5 ka。其余特征清晰的暖期事件与GIS#8对应，但该事件的强度远弱于GIS#12，且发生于一段以生长速率偏低、δ¹³C值偏高为特征的较冷时段内。2）对应格陵兰冰段（Greenland Stadials, GS）的冷期事件，其典型特征为石笋δ¹³C值偏高、温带孢粉丰度偏低、气温降低且干燥程度加剧，该特征在与海因里希事件（Heinrich events）H5和H4同期的格陵兰冰段中表现尤为明显。维拉尔洞穴序列的核心特征是，在DO#12事件（约45.5 ka）至三支石笋同步停止生长（约30 ka±1）的时段内，整体呈现降温趋势；其中约41 ka处存在一个显著的气候阈值，此后所有石笋的生长速率与直径均出现明显减缓。这一气候演化过程与地中海南部站点的记录存在差异，后者并未观测到该降温趋势。[…]