Asian paleoclimate reconstruction from Siberian and Mongolian speleothems

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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.