Holocene climate variations retrieved from Gun Nuur lake-sediment core in the northern Mongolian Plateau

摘要

Our pollen-based climate reconstruction shows that both temperature and moisture were low during the early Holocene from -10,000 to -8000 cal. a BP and gradually climbed from -8000 to -6000 cal. a BP. The last -6000 years have been generally warm and wet with high-amplitude fluctuations. The high-moisture conditions for the past -6000 years are not only corroborated by high arboreal pollenon-arboreal (AP/NAP; trees and shrubs over herbs) pollen ratio and high pollen concentration but also by high organic matter content and diatom data. We suggest that lower winter insolation and remaining ice covers in the early Holocene might have slowed down temperature rise in the continental interiors and that the resulted low temperature might have suppressed regional evaporation that was a major water vapor source for precipitation. At the same time, icemelt-water injection into the North Atlantic Ocean might have also suppressed water vapor supplies to the downwind areas, including the northern Mongolian Plateau. The increase in winter insolation and the final melting of ice sheets, together with the increased atmospheric CO_2 concentration and the associated increase in atmospheric water vapor, could be responsible for the higher temperature during the past -6000 years. The icemelting and the associated rise of sea level during the past -6000 years might be responsible for the weakening of the winter monsoon in the interior of Asian continent, thus alluring farther eastward penetration of the relatively warm and wet Atlantic air masses and consequently bringing more precipitation to the northern Mongolian Plateau.