华北倒二冰消期的气候变率及相位关系：高分辨石笋记录

A series of questions about the penultimate deglaciation have continuously been raised by emerging paleoclimate data since the launch of the oxygen isotope sequences of calcite veins from Devils Hole, such as"causality problem", "one or two phase problem", "variability problem" and so on. The problems of the penultimate deglaciation have become relatively independent paleoclimate research branch. Over the past years, high-precision dating of stalagmite records from the South China of the East Asian monsoon region provides a new time framework for the analysis and discussion on the mechanism of glacial termination, but also reveals many discrepancies between stalagmite records themselves, as well as with other records. It could gives us hope to understand and answer these questions to obtain new records from northern China, another key area of the East Asian monsoon region. Here we propose the stalagmite XL-4 from Xinglong Cave located in northern China, which covers the complete penultimate deglaciation with no hiatus. The preliminary analysis indicates that the precision of its uranium series dating is better than 0.5%. And moreover, it could be expect to improve the precision by enlarging sample size. With accurately sampling using Micromill, stable isotope analysis could be able to mill up to 13 subsamples/mm, it means that the average resolution of the time series could be reached 5a. Based on the establishment of high-resolution stable isotope sequence controlled by precise time scale, this stalagmite record will reveal climate variability and phase relationship (with respect to insolation and other records) during the penultimate deglaciation in northern China, which may help to understand some major scientific questions such as the interaction between high and low latitude, the relationship between internal and external forces, as well as the solution of the "causality problem".

自从Devils Hole方解石脉的氧同位素序列发表以来，倒二冰消期的"因果问题"、"阶段性问题"以及"气候变率问题"不断被新的古气候记录提出并刷新。过去数年，来自东亚季风区中国南方的高精度定年石笋记录为冰期终止机理的分析和讨论提供了新的年代框架，同时也发现了石笋记录本身、以及石笋记录与其他记录之间在倒二冰消期不吻合。如何进一步理解和回答这些问题？从东亚季风区另一关键区域华北获得新记录是希望之一。申请者最近获取的河北兴隆洞石笋XL-4跨完整倒二冰消期时段，无沉积间断，初步定年分析表明其铀系年代精度优于0.5%。若稳定同位素分析采用Micromill精确取样，可实现13个样/mm，平均分辨率达到5a。在建立具有精确时标的高分辨稳定同位素序列基础上，揭示倒二冰消期华北的气候变率与相位关系，将有助于对高低纬相互作用，及内外力驱动关系等重大科学问题的理解，并有助于解决"因果难题"。

与已经研究得非常充分的末次冰消期相比，倒二冰消期的发生时间和结构仍存在争议，因为该时段高质量地质记录比较匮乏。本研究对采集于河北兴隆洞的一根沉积于133.4±0.3和126.6±0.3 ka BP之间，包含倒二冰消期主要过程的石笋样品XL-4进行了高精度的铀系年代（精度优于3‰）和高分辨率的氧碳同位素比值分析（平均分辨率38年）。XL-4氧同位素比值时间序列显示华北末次间冰期开始于129.4±0.3 ka BP，与中国南方石笋记录一致，进一步说明北半球高纬夏季太阳辐射是驱动冰期终止的关键因子。在末次间冰期开始之前，XL-4记录有一个持续数千年的氧同位素比值正偏事件，即“倒二冰消期弱季风时段”，对应于北大西洋冰筏事件Heinrich 11。在这个“弱季风时段”内，兴隆洞石笋记录又出现了一个持续约1600年的氧同位素比值负偏事件（中心位于132.7±0.3 ka BP）。相似的间冰段事件在南方石笋和北大西洋记录中也有所表现（持续时间和变化幅度存在一些差异）。因此，我们推测北大西洋冰筏事件Heinrich 11主体部分发生于132 ka BP之后，而在此之前，海洋和大气环流仍主要处于间冰段气候模式。XL-4记录在末次间冰期开始后，出现了一个千年尺度的氧同位素比值波动事件（中心位于128.4±0.3 ka BP），对应于南方石笋的氧同位素比值负偏变率减缓事件，一些北大西洋记录也呈现了类似的增温暂停事件。由于该事件变化幅度小，因此并不能类比于新仙女木事件，可能是因为倒二冰消期北半球高纬夏季太阳辐射更强，大气二氧化碳浓度更高，引起冰盖更早更快的消融，使更多的淡水注入北大西洋。此外，南方石笋氧同位素比值在128 ka BP达到最低值，即深海氧同位素5阶段的峰值（MIS 5e），随后开始呈持续正偏趋势。然而，XL-4记录在末次间冰期初期的氧同位素比值波动之后，呈持续负偏趋势，直到石笋停止生长（126.6±0.3 ka BP）。由此推测，与南方石笋不同，北方石笋记录的MIS 5e很可能是末次间冰期以来岁差旋回的最高峰，可能是由于冰量即全球温度变化背景在北方记录中打上了烙印，即地质温度计起了作用（北方温度变化大于南方）。