全球变化知识资源中心

The semi-arid areas at the northern margin of the East Asian summer monsoon (EASM) have experienced an increased frequency of drought in recent decades. However, it is unclear whether past monsoonal precipitation in the region were determined mainly by El Nino-Southern Oscillation (ENSO) variability or high-latitude cooling. In this study, we use a high-resolution grain-size dataset combined with a new Bayesian age depth model of a sediment core from Dali Lake to analyze the occurrence of millennial- and centennial-scale droughts at the EASM margin during the interval of climatic warming during the last deglaciation. The polymodal grain size distributions are partitioned using a log-normal distribution function fitting method. High percentages of the coarse components (C4 + C5 + C6) are recognized as proxy indicators of strong aeolian activities and low lake levels, and thus droughts in the region. The drought events indicated thereby are generally accompanied by decreases in regional temperature, catchment surface runoff and bio-productivity, on both millennial and centennial timescales. These results imply that the droughts at the EASM margin were caused by a significantly weakened EASM intensity. In addition, the droughts may be linked, within the age uncertainties, to the Heinrich 1 (H1) and Younger Dryas (YD) events on millennial timescales, and to the Older Dryas (OD) cold event on centennial timescales, implying strong high-latitude forcing. Given that these cold reversals over northern high latitudes were induced by the rapid input of glacial melt-water to the North Atlantic during the last deglaciation, it is possible that ongoing climatic warming, and the resulting high northern-latitude ice-sheet melting, may cause an increased incidence of drought in northern China.