新疆SCZ17剖面黑碳记录的16~12 ka火灾历史及其驱动因素探究

基于新疆深390 cm的SCZ17黄土剖面的黑碳(BC)记录以及总有机碳含量(TOC)和磁化率结果,并与巴里坤湖孢粉记录的温度数据对比,重建了该区末次冰消期(16~12 ka,对应剖面深度202~274 cm)的火灾历史并探讨了其控制因素。结果表明:1)在末次冰消期期间黑碳通量与TOC变化具有较好的一致性,均呈上升趋势,说明随着植被量的增加,生物质燃烧活动增加;2)BC通量与湿度和温度数据的EEMD结果显示:①在13~16 ka期间,剖面的黑碳通量指示的区域生物质燃烧变化与温度变化存在着近乎同步的关系,而在12~13 ka期间可能由于湿度的影响二者的同步关系不太明确;②χfd%所指示的湿度变化和黑碳通量的对比结果显示,湿度峰值/谷值分别对应着黑碳通量的谷值/峰值,即当气候湿润时,火灾活动频率低;气候干旱时,火灾活动频率高。因此,认为研究区火灾活动倾向于发生在暖干的气候条件下,且可燃生物量可能控制着区域火灾变化的长期趋势,而由温度和湿度变化所造成的火灾活动的次一级波动叠加在这一长期趋势上。

A STUDY ON THE FIRE HISTORY AND ITS DRIVING FACTORS DURING 16?12 KA BASED ON BLACK CARBON IN SCZ17 SECTIO N,XINJIANG

Based on the analysis of black carbon(BC),total organic carbon content(TOC)and magnetic susceptibility of SCZ17 loess profile(43°37'2.34"N,89°45'31.67"E;1752 m a.s.l.),compiled with the published pollen data from Balikun Lake(43°36'~43°45'N,92°42'~92°54'E;1575 m a.s.l.),the history of the paleo fire and its relationship with climate change in arid Central Asia during the last deglaciation were discussed.The profile is located in the the Bogda Mountains,part of the eastern Tienshan Mountains in Xinjiang,China.This area is characterized by a typical temperate continental climate and receives water vapor carried by the Westerlies.The SCZ17 profile is 390 cm in thickness and a total of 195 samples were taken at 2 cm interval.In this study,we focus on the part between 202 cm and 274 cm,corresponding to the period of last deglaciation(16~12 ka).The chronology framework of the profile was established by three coarse-grained quartz optically stimulated luminescence(OSL)ages,measured in Key Laboratory of Western China's Environmental Systems,Lanzhou University.The results show that:(1)The trend of BC flux showed a similar upward trend to TOC during the last deglaciation,indicating that the fire activities increase when vegetation cover increases;(2)The contrast analysis of results of ensemble empirical mode decomposition(EEMD)of BC flux and frequency-dependent magnetic susceptibility(χfd%)from SCZ17 section and pollen data from Balikun Lake show that:①during 16~13 ka,there was a nearly synchronous variation between fire activities and temperature changes,however this relationship is not clear during the 13~12 ka which may be due to the influence of humidity indicated byχfd%;②the peak/valley value ofχfd%is corresponds to the valley/peak value of BC flux,which means there is less fire activities when the climate is humid while more fire activities occurred when the climate is dry.In summary,the fire activities in the study area tend to occur in warm and dry climates,and the combustible biomass may control the long-term trend of regional fire changes.The fluctuations of fire activities caused by temperature and humidity changes are superimposed on this long-term trend.