The Heinrich Events During The Period Recorded By The Stalagmites In Yangkou Cave, Chongqing

Global warming has become the focus of global concern. Global climate change is no longer just a discipline problem and is becoming a major social issue of most concern in today’s human society, it is closely related to the survival of the human environment. The most typical characteristic of climate change in the last glaciation is a series of centuries-millennial scale climate fluctuations, the Heinrich (H) events and Dansgaard-Oeschger (D/O) cycles. At present, due to the lack of high-resolution dating of the geological record, the beginning and ending of H events and duration as well as the internal structures are still controversial, and its climate-driven mechanisms have not yet been fully realized clearly. The stalagmite has been one of the most concerned paleoclimatic informations in geoscience field which follows the study of marine sediment, ice-core, lake, and loess. Thanks to its high resolution, possibility to extract rich information parameter, and long time span, it has an irreplaceable advantage in restoring paleoclimate and environmental changes in both interannual and seasonal time-scale compared with other geologic records.The YK1 and JFYK7, from Chongqing Yangkou cave, are the research objects. By means of the high-resolution TIMS-U dating and oxygen isotope record, the paleoclimate changing time sequence with high resolution, spaning the period, is established to reveal the regularity of climate change in this region. And with comparison of other geological records worldwide, using the method of RAMPFIT fitting, accurately calibrated the H1-H6 events and analyzed the reasons of the different beginning and ending of H events as well as their internal structure in other geological records. Then discussing the Asian monsoon circulation pattern and the relationship between the Greenland temperature and the Antarctic temperature.Through analysing the high resolution δ18O records of YK1 and JFYK7 in Yangkou cave, the stalagmites of YK1 and JFYK7 meet the Hendy test, they have good reproducibility, so we can use the δ18O records of YK1 and JFYK7 reconstructing the paleoclimate. By contrast, the H events recorded by the stalagmites in Yangkou Cave are agree with other geological records, indicating that the stalagmites in Yangkou Cave are able to respond to the climate change, controlled by the change of the Asian summer monsoon jointly, during the H events, Asian summer monsoon weakened and the δ18O values of stalagmites enriched obviously. The δ18O records of stalagmites have a good relationship with the solar radiation on the long time-scale, but on the short time-scale they are not well corresponding. Many factors can influence the δ18O values of stalagmites, mainly temperature, precipitation and evaporation, the ratio of winter and summer precipitation, water vapor source, and atmospheric circulation.Using the δ18O records of stalagmites of YK1 and JFYK7 in Yangkou cave in Chongqing reconstructing the change of the Asia monsoon in the period of 15～78 ka BP. At the same time, by using the method of RAMPFIT fitting, accurately calibrating the beginning and ending of Heinrich events and analysising the internal structure of H events through comparing with other records worldwide. Comparing with the Xinya cave, Xiao Bailong cave, Dongge cave, Hulu Cave and Sanbao cave in the same area of Asian monsoon region, showing that the change of composition of δ18O in precipitation has spatial consistency over a wide range on millennium-scale in Asian monsoon region. But the stalagmites in Yangkou Cave have higher resolution, the more accuratly dating make the calibration of H events more reliable.The events of H1-H6 recorded in stalagmites in the East Asian monsoon region reflect the weakening of summer monsoon, corresponding to lower temperature of ice core records in North Atlantic Greenland. Furthermore, stalagmites in the Indian monsoon region also record this event, representing weakening of the summer monsoon. The δ18O values of stalagmites in the Southern Hemisphere are in contrast with that of the Northern Hemisphere, during the H events the intensity of the summer monsoon in Southern Hemisphere has increased, matching with the higher temperature of ice core records in the Antarctic. This also explains the anti-phase relationship between the Northern and Southern Hemispheres on the millennium scale. But the geological records are not consistent entirely, reflecting regional differences.The changing patterns of H2, H3 and H4, recorded by stalagmites in Asian monsoon region, are similar to the changes of the temperature recorded by the EDML ice core in Antarctic, indicating that in the last glaciation the East Asian summer monsoon can not only reflect signals at high latitudes in the Northern Hemisphere, but also be affected by the change of the temperature in Southern Hemisphere. North Atlantic Meridional Circulation (AMOC) is the main reason for the abrupt climate change of the Asian monsoon. The climate signals of higher latitudes in Northern Hemisphere majorly impact the strength of Asian summer monsoon by westerly, thereby affecting the change of δ18O values in stalagmites and the median particle size of loess. The reason of the teleconnections between the climate of North Atlantic region and the Asian monsoon is that when the solar radiation weakens, the Greenland temperature decreases, the thermal contrast of the land-sea reduces, finally leading the Asian summer monsoon weakening. When the H events have happened, the Siberian high pressure becomes increased, the temperature of the Northern Hemisphere has descended, in this case, the ITCZ moves southwards, leading the Asian winter monsoon strengthen and the duration increase, then the summer monsoon circulation weakens. The migration of the ITCZ is caused by the gradient of temperature between the Northern and Southern Hemispheres, the ITCZ tends to the warmer Hemisphere. The migration of the ITCZ is related to the AMOC, when the AMOC weakens, the ocean heat transporting northward is reduced, the sea surface temperature decreases, the Northern Hemisphere becomes cold, finally pushing the ITCZ to southward.