High-resolution climate evolution derived from the sediment records of Erlongwan Maar Lake since 14 ka BP

Varve counts with AMS 14 C,137 Cs and 210 Pb dating of sediments(0-900 cm) from Erlongwan Maar Lake,NE China were used to establish a high-resolution chronology series for the late Quaternary.Dry density,total organic carbon(TOC) content,total nitrogen(TN) content,TOC/TN ratios and stable organic carbon isotope(13 C org) ratios were continuously analyzed on this sediment profile.On the basis of lithological characters,sporo-pollen assemblages and geochemical analyses,we identified 6 climate stages within the last 14 ka BP.The time before the Holocene(14-11.4 ka BP) represents a higher-order oscillation climatic transitional period(I).The entire Holocene climate development(from 11.4 ka BP to present) exhibited an increasing temperature trend,although there were cold and warm alternations(II-VI).The periods included were:II(11.4-9.05 ka BP) warm-wet stage,III(9.05-7.4 ka BP) cold and warm fluctuation stage,IV(7.4-4.2 ka BP) smoothly warming climate stage,V(4.2-1.67 ka BP) climate optimum stage,and VI(from 1.67 ka BP to present) cool and drier stage.Each climate stage began with a warming event and ended with an abrupt cooling event.This climate change cycle had unequal time spaces that were progressively shorter over time.Several abrupt climate shifts occurred at about 9.4-9.05,8.5-8.2,7.8-7.4,4.6-4.2,3.7-3.25,2-1.67 and 0.3-0.03 ka BP.Thus,it can be seen that the climate has been warming since 1920 AD,which indicates a new climate stage.

Varve counts with AMS 14C, 137Cs and 210pb dating of sediments （0-900 cm） from Erlongwan Maar Lake, NE China were used to establish a high-resolution chronology series for the late Quaternary. Dry density, total organic carbon （TOC） content, total nitro- gen （TN） content, TOC/TN ratios and stable organic carbon isotope （δ13Corg） ratios were continuously analyzed on this sediment profile. On the basis of lithological characters, sporo-pollen assemblages and geochemical analyses, we identified 6 climate stages within the last 14 ka BP. The time before the Holocene （14-11.4 ka BP） represents a higher-order oscillation climatic transitional period （Ⅰ）. The entire Holocene climate development （from 11.4 ka BP to present） exhibited an increasing temperature trend, alt- hough there were cold and warm alternations （Ⅱ-Ⅵ）. The periods included were： Ⅱ （11.4-9.05 ka BP） warm-wet stage, Ⅱ （9.05-7.4 ka BP） cold and warm fluctuation stage, Ⅳ （7.4-4.2 ka BP） smoothly warming climate stage, Ⅴ（4.2-1.67 ka BP） cli- mate optimum stage, and Ⅵ （from 1.67 ka BP to present） cool and drier stage. Each climate stage began with a warming event and ended with an abrupt cooling event. This climate change cycle had unequal time spaces that were progressively shorter over time. Several abrupt climate shifts occurred at about 9.4-9.05, 8.5-8.2, 7.8-7.4, 4.6-4.2, 3.7-3.25, 2-1.67 and 0.3-0.03 ka BP. Thus, it can be seen that the climate has been warming since 1920 AD, which indicates a new climate stage.