Quantitative pollen-based paleoclimate reconstructions for the past 18.5 ka in southwestern Yunnan Province, China

Quantitative reconstruction of past climate plays an important role in understanding global and regional climate changes and validating climate models. Although some important progress has been made in quantitative paleoclimate reconstructions based on terrestrial records in the Indian summer monsoon region, high-resolution quantitative studies spanning the last similar to 20 ka are still relatively sparse with differing results. This study presents high-resolution quantitative variations in mean temperature of the coldest month (MTCM, the first controlling factor of the regional vegetation), mean annual temperature (MAT, the second controlling factor), and mean annual precipitation (MAP) from Lake Tengchongqinghai in southwestern China, based on an updated modern pollen dataset and the fossil pollen record spanning the last 18.5 ka. The results show that temperature and precipitation increased gradually from 18.5 ka, and peaked from 7.2 to 4.5 ka when MAT was on average 1.0 degrees C higher than the modern observational value (14.5 degrees C), corresponding to the mid-Holocene thermal maximum (HTM), and then decreased gradually. The total reconstructed ranges are between-2.2 and 9.2 degrees C for MTCM, 7.7 and 17.2 degrees C for MAT, and 840 and 1300 mm for MAP. On top of this overall climate trend, seven abrupt cold and dry events were detected during the periods of 16.2-14.8 ka, 12.8-11.5 ka, similar to 11.1 ka, 9.1-8.4 ka, similar to 7.7 ka, 4.3-3.7 ka, and 0.68-0.009 ka (1270-1950 CE). The results of this quantitative reconstruction were validated by both statistical and ecological evaluations. We conclude that the trend of climatic change since 18.5 ka in this study area was primarily driven by June, July, August, and September solar insolation and changes in radiative forcing and greenhouse gas concentrations. The abrupt changes may be caused by changes in the Atlantic meridional overturning circulation, solar activity, the position of the Intertropical Convergence Zone, and volcanic activity.