Asian paleoclimate reconstruction from Siberian and Mongolian speleothems

我建议使用洞穴碳酸盐（钟乳石和石笋，统称为洞穴沉积物）来重建过去400万年（Ma）西伯利亚气候变冷和戈壁沙漠干燥的历史，以及它们与亚洲和全球气候变化的关系。高、中、低纬度气候变化之间的联系仍然知之甚少，全球气候变冷与过去4 Ma世界大沙漠发展之间的关系也是如此。e.上新世和第四纪地质时期）。目前，亚洲内陆的温度控制着冬季和夏季亚洲季风的强度和持续时间。在一年中较冷的下半年，西伯利亚和蒙古上空的高气压造成了干燥和寒冷的冬季季风条件，阻止了水分到达亚洲内陆。中国黄土沉积物中的古气候记录表明，从北方约2.6Ma前的初始冰川作用开始的逐步冷却与戈壁沙漠在约2.6Ma、约1.2Ma、约0.7Ma和约0.2Ma的扩张之间可能存在联系。这项工作还表明，沙漠的扩张/收缩可能分别与冰期/间冰期有关。然而，西伯利亚变冷年代的不确定性使得很难确定西伯利亚变冷=戈壁变干的关系是否稳健，并妨碍了对这些变化的相对阶段性进行评估。戈壁在上新世和第四纪是否也有暖干期？如果答案是否定的，这意味着未来的全球变暖预计将导致戈壁气候的改善。如果答案是肯定的，那么在未来更温暖的世界中，该区域有可能进一步荒漠化。洞穴沉积物可以精确地定年（使用U-Th和U-Pb技术），并提供了回答这些时间问题的潜力。我将使用这些方法精确地确定西伯利亚南部温暖时期和蒙古戈壁沙漠潮湿时期的日期。只有当液态水渗入洞穴时才形成洞穴积土，因此在冰冻或干旱的条件下不会形成。因此，洞穴沉积物生长期的测定可以评估西伯利亚平均气温高于冰点的时期，以及戈壁沙漠潮湿时期的情况。西伯利亚和蒙古没有现存的洞穴沉积物记录。事实上，除了在南方季风区的一些重要工作（e。G.中国和印度），整个亚洲都完全缺乏这样的记录。然而，在西伯利亚和蒙古有丰富的洞穴，具有良好的洞穴沉积物目标的古气候工作。我已经在这些国家建立了一个合作者团队，他们拥有确保我能够进入这些洞穴并在其中工作所需的经验，并对该地区进行了初步访问，以确认这些合作并访问一个重要的洞穴遗址。在洞穴沉积物生长期间，还将分析其稳定同位素组成。氧同位素比率将用于探测大气降水的来源和数量的变化。碳同位素的变化反映了洞穴上方北方森林植被与草原植被的变化。因此，这些同位素系统将允许重建过去的水文和植被状态与高精度的年代框架。这项工作将通过对该地区现代洞穴环境的评估以及对当今水的氧和氢同位素与气候变量之间的现代关系的研究来提供信息。新的洞穴沉积物记录将提供有关广阔亚洲内陆气候控制的有力信息，对该地区应对未来全球变暖具有重要意义。

I propose to use cave carbonates (stalactites and stalagmites, collectively named speleothems) to reconstruct the last 4 million year (Ma) history of climate cooling in Siberia and of drying in the Gobi Desert, and their relationship to Asian and Global climate changes. Connections between the climate changes in high, middle and low latitudes are still poorly understood, as is the relationship between global climate cooling and the development of the world's large deserts during the last 4 Ma (i. e. the Pliocene and Quaternary geological periods). At present, the temperature of the Asian interior controls the intensity and duration of the winter and summer Asian monsoon. During the colder half of the year the high atmospheric pressure above the Siberia and Mongolia is responsible for dry and cold winter monsoon conditions, preventing the moisture from reaching the Asian interior. Existing paleoclimate records from loess sediments in China indicate possible linkage between stepwise cooling, starting with the initial glaciation of the Northern Hemisphere ~2.6Ma ago, and the expanding of the Gobi Desert at ~2.6Ma, ~1.2Ma, ~0.7Ma and ~0.2Ma. This work also suggests that expansions/contractions of the desert may correlate with glacial/interglacial periods respectively. Uncertainty in dating of the cooling of Siberia makes it difficult, however, to determine if this relationship Siberian cooling = Gobi drying, is robust, and prevents assessment of the relative phasing of these changes. Did warm and dry periods also occur in the Gobi during the Pliocene and Quaternary? If the answer is no, it means that future global warming is expected to cause amelioration of the Gobi climate. If the answer is yes, there is a potential of the further desertification of the region in the future warmer world. Speleothems can be precisely dated (using U-Th and U-Pb techniques) and offer the potential to answer these timing questions. I will precisely date warm periods in southern Siberia and wet periods in the Mongolian Gobi Desert using these methods. Speleothems form only when liquid water seeps into caves and therefore do not form when conditions are frozen or arid. Dating of speleothem growth periods therefore allows an assessment of periods when the mean temperatures in Siberia were above freezing, and when wet periods occurred in the Gobi Desert. There are no existing speleothem records from Siberia or Mongolia. In fact, apart from some important work in the monsoon regions of the south (e. g. China and India), there is complete lack of such records from whole Asia. There are, however, abundant caves with good speleothem targets for paleoclimate work in Siberia and Mongolia. I have established a team of collaborators in these countries with the experience required to ensure that I can access and work in these caves, and have made a preliminary visit to the region to confirm these collaborations and to visit one important cave site. During periods of speleothem growth their stable isotope composition will also be analyzed. Oxygen isotope ratios will be used to detect changes in origins and amounts of atmospheric precipitation. Carbon isotopes may reflect the changes between boreal forest and steppe vegetation types above the caves. These isotope systems will therefore allow reconstruction of past hydrological and vegetation states with a high-precision chronological framework. This work will be informed by assessment of the modern cave environments in the region, and by study of the modern relationship between the present-day water oxygen and hydrogen isotopes and climate variables. The new speleothem records will provide powerful information about the controls on climate in the vast Asian interior, with important implications for the response of this region to future global warming.