VARIABILITY OF EASTERN ASIAN SUMMER MONSOON DURING 2. 8 KA CLIMATE EVENT RECORDED IN A STALAGMITE OXYGEN ISOTOPE SEQUENCE FROM MIAODONG CAVE, NORTHEASTERN CHINA

The 2.8 ka cold event is one of well known abruptly climate events during the Late Holocene. Previous documents showed weak Eastern Asian Summer Monsoon(EASM) and less precipitation in the northern margin of EASM area during 2.8 ka event. The forcing of this event has been pointed to Solar activity, but the detail forcing mechanism is still unclear. Considering the significantly negative excursion of solar activity during 2.8 ka, high resolution record of EASM with well age constraining is helpful for us to better understand this mechanism. In this study, stalagmite MD12 from Miaodong Cave(41°03‘N, 125°31‘E), Northeastern China were analyzed. The mineral composition of stalagmite MD12 is pure calcite. Total of 5 230Th dating were performed on MC-ICPMS. Total of 90 subsamples for stable isotope measurement were drilled(80 along the vertical growth axle and 10 along horizontal layer at 2 depths for “Hendy Test”), and analysed with MAT 253 coupling with Gasbench-?. The MD12 isotope sequence covers interval of 2.92~2.60 ka B. P. The MD12 sequence was then composited with the other published oxgen isotope time series also from Miaodong cave, named MD11, to build the Miaodong stalagmite oxygen isotope sequence covering 3.04~2.60 ka B. P. The variability of Miaodong stalagmite oxygen isotope is interpreted as change of EASM intensity or monsoon precipitation in this area. Based on these ages with low errors(two sigma, 18 to 25 years), the Miaodong record give a detail evolution of EASM and precise transfer time of 2.8 ka event. From 2.88 ka B. P. to 2.62 ka B. P., the Miaodong record exhibits two weak EASM intervals, 2.81~2.87 ka B. P. and 2.76~2.66 ka B. P. respectively. The later one, covering about 110 years, is the key interval of 2.8 ka event, and exhibits a symmetrical shifting process. The EASM abruptly decrease at around 2.76 ka B. P., and reached its worst state at about 2.68 ka B. P., following by an abruptly strengthening process. This transfer point(2.68 ka B. P.) is little younger than those stalagmite records from Southwestern China(around 2.71 ka B. P.), but coincides with the solar minimum and cold event around Greenland Island well. In general, the evolution of EASM indicated by Miaodong record corresponds to those of total solar irradiance(TSI) without any delay, indicating solar activity forcing via a fast dynamic mechanism. Unlike with southwestern records which show gradually decrease of EASM from about 2.88 ka B. P. until 2.71 ka B. P. and abruptly increase from then on. The instantaneously response of Miaodong record to ?TSI without any delay indicates that the decrease of TSI maybe results in intense cold climate in the area surrounding the Greenland Island and the Northern Atlantic, and then decreases the EASM via atmospheric remote-correlation.