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.
