PIRE: DUST stimulated drawn-down of atmospheric CO2 as a trigger for Northern Hemisphere Glaciation

了解过去5000万年来长期全球变冷的地质过程对于了解今天地球上的气候条件非常重要。400万年前，北方半球基本上没有冰，随后在大约360万年前全球气温加速下降，大约270万年前，北方半球大陆上的大陆冰盖开始形成。有限的大气CO2记录表明，在这段时间内，CO2从约400到约300 ppm（ppmv）的下降可能使地球充分冷却，使冰盖生长。然而，二氧化碳减少的原因仍然未知。这项由7个美国和3个中国机构组成的国际研究和教育合作将评估一个新的假设：来自中亚沙漠的大气尘埃使北太平洋肥沃，刺激藻类生产力，从而降低大气中的二氧化碳，导致北方半球冰川（NHG）。通过在中国的实地工作研究，海洋和陆地沉积物的实验室分析，以及大气和海洋建模研究，研究人员和学生将生成和比较来自不同地质档案的广泛的古气候记录，以评估NHG开始时大气尘埃在CO2下降和全球冷却中的作用。 该研究项目的结果最终可能有助于对全球政策产生影响的知识。通过评估大气尘埃在维持地球凉爽气候条件方面的重要性，该研究有望阐明近期地质历史中气候变冷的机制。具体而言，本研究将建立以下记录：1）中亚、西藏北方和中国黄土高原（CLP）的干旱化历史，与这些地区及其以西的高亚洲地区的变形和地表隆起记录有关，2）中亚盆地的风蚀和CLP地区的沙尘堆积，3）沙尘通量、藻类生产力，4）陆地CO_2的变化时间为4.5- 2.5Ma。模拟和敏感性研究将（1）评估亚洲气候和沙尘循环对地形变化和背景全球气候的敏感性;（2）确定上新世沙尘输送到北太平洋可能导致的冷却量;（3）评估亚洲沙尘对大气CO2的潜在影响。通过该研究项目，美国研究生将有机会进入中国的研究设施和实地考察，并通过双边访问与中国合作伙伴开展互利的合作研究活动;美国本科生也将有机会参加暑期学校，研讨会和研究项目;研究人员将为博物馆开发外展工具，以提高公众对大气尘埃在气候变化中的作用的认识。

Understanding the geologic processes underlying the long-term global cooling over the past 50 million years (myr) is important for understanding the climate conditions on Earth today. The Northern Hemisphere was largely ice-free 4 myr ago followed by an acceleration of global temperature decline at ~3.6 myr ago, with continental ice sheets developing on northern hemisphere continents by ~2.7 myr ago. Limited atmospheric CO2 records suggest a decline in CO2 from ~400 to ~300 parts per million by volume (ppmv) during that time period could have cooled the Earth sufficiently to enable ice sheets to grow. Yet the cause for this decline in CO2 remains unknown. This international research and educational collaboration between 7 U.S. and 3 Chinese institutions will evaluate a new hypothesis: atmospheric dust derived from Central Asian deserts fertilized the North Pacific ocean, stimulating algal productivity, which in turn drew down atmospheric CO2 leading to Northern Hemisphere Glaciation (NHG). Through field work studies in China, laboratory analyses of ocean and terrestrial sedimentary deposits, and atmospheric and ocean modeling studies, the investigators and students will generate and compare a wide range of paleoclimate records from diverse geological archives to evaluate the role of atmospheric dust in CO2 decline and global cooling at the onset of NHG. The findings from this research project may ultimately contribute to knowledge with global policy implications.By evaluating the significance of atmospheric dust in sustaining cool climate conditions on Earth, this study is expected to elucidate the mechanisms of climate cooling in the recent geologic past. Specifically this study will establish records of: 1) the aridification history of Central Asia, northern Tibet, and the Chinese Loess Plateau (CLP) as related to records of deformation and surface uplift in high Asia within and to the west of these regions, 2) wind erosion of Central Asia basins and dust accumulation in the CLP, 3) dust flux, algal productivity, and sea surface temperature in the North Pacific and South Atlantic, and 4) terrestrial CO2 in the interval of 4.5-2.5 Ma. Modeling and sensitivity studies will (1) evaluate the sensitivity of Asian climate and the dust cycle to the growth of topography and to the background global climate; (2) determine the amount of cooling that could result from Pliocene dust transport to the North Pacific; (3) evaluate the potential influence of Asian dust on atmospheric CO2. Through this research program, US graduate students will gain access to research facilities as well as field localities in China that would otherwise be inaccessible and engage in mutually beneficial collaborative research activities with Chinese partners via bilateral visits; US undergraduate students will also have the opportunity to participate in summer schools, workshops, and research projects; the investigators will develop outreach tools for museums to increase public understanding of the role of atmospheric dust in climate change.