The Relationship Between Asian Summer Monsoon And Global Climate Change During The Last Glacial Period

Global climate has been in a constant process of change, and the human be directly or indirectly affected by the climate change in many aspects. The research on global climate change is becoming a major social issue of most concern in human society. It is necessary to study and master the process and mechanism of the past climate change to predict the future trend of climate change. In recent decades, people use the geological records, such as stalagmites, ice core, marine, loess, lake, etc., to study the climatic events during the last glacial period(LGP) have achieved fruitful results. The most typical characteristic of climate change in the LGP is a series of centuries-millennial scale climate fluctuations, the Dansgaard-Oeschger(D/O) cycles and Heinrich(H) events. At present, due to the lack of high-resolution dating of the geological record, the beginning and ending of D/O and H events and the patterns of change etc., 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 information in geoscience field thanks to its high resolution compared with other geologic records.In this paper, we use the stalagmite JFYK7 and YK1327 with the 238 U content of 5.3-13.9 ppm, 61 high precision 230 Th data, 1895 oxygen isotope, from Yangkou Cave, Chongqing, to reconstruct the evolution of the Asian summer monsoon(ASM) during the LGP from 37.8 to 99.2 ka BP. Through the comparison of other geological records worldwide to analyses the difference of the phase difference and the change pattern of the D/O and H events. Then discuss the relationship between the ASM and the global climate change and its climate-driven mechanism.We found the trend of the δ18O changes recorded in the Yangkou stalagmite records with the variation of the 33 °N summer insolation is consistent. Suggesting the change of the ASM in Chongqing responded to the variation of the summer insolation in orbit-scale. Moreover, the ASM is also affected by the temperature changes in the high latitude and the pressure belts in the mid-low latitude of the Northern Hemisphere(NH) and Southern Hemisphere(SH). A comparison with the NGRIP records shows that the millennium-scale events(D/O 8-22 and H 4-6) documented in Greenland ice cores from high latitudes in the NH are also present in the JFYK7 and YK1327 records. The similarity between Yangkou records and NGRIP indicates that ASM have mainly responded to temperature changes in high latitudes of the NH. One of the dramatic characteristics of D/O events recorded by the NGRIP is the abrupt and rapid temperature increase at the onset of the period and slow cooling at the end. This asymmetric feature is not prominent in the stalagmites records from Yangkou cave, and the δ18O value became increasingly negative like the pattern of the temperature change recorded in the Antarctic ice core; The pattern of the H 4 event recorded in Yangkou records is different to the pattern of the temperature change recorded in the Antarctic ice core, and show the shape of the "V"; The end time of the H 5 event was earlier than the NGRIP records; The weakening variation pattern of the ASM is different from the rising pattern of the temperature recorded in NGRIP and similar with the Antarctic ice core records. It is possible that the records in the ASM influenced by temperature changes in the SH. The overall changes in JFYK7 and YK1327 stalagmites records and other stalagmites records in Chinese monsoon region are analogous, but some differences of the D/O and H events exist. The differences should be attributable to the regional differences of summer monsoons or the difference in model age and resolution in different records. Additionally, when comparing the records from Yangkou with Indian summer monsoon region, there is a significant difference in patterns at the beginning of D/O events and the ending of H 5. And the records from the Indian summer monsoon region are consistent with the NGRIP record. This change may be related to the global ocean conveyor belt controled by the temperature in high latitude in NH during this period. The time of the weakest summer monsoon during H 5, as recorded in the Indian summer monsoon(ISM) records, is later than JFYK7 and NGRIP records ~1 ka. It is possible that, during the H 5 period, the temperature in the SH continuous warming and reached the highest, the Hadley circulation intensity in the Southern Hemisphere decreased. Simultaneously, the southeast trade winds(STW) in the Southern Hemisphere gradually weakened, resulting in the weakening of the ISM and eventually the weakest ISM at ~47.2 ka BP. The stalagmites from Yangkou cave and the other geological records in SH affirmed the ―see-saw‖ effect and ―anti-phase‖ characteristics of climate changes in the SH and NH.The transmission of the signal of the temperature change in the North Atlantic region is mainly by the westerly belt and the ocean conveyor belt, and then influenced the ASM. The temperature changes in the SH affect the ASM by affecting the position of the tropical convergence belt(ITCZ), the intensity of the Hadley circulation, the changes of Mascarene High(MH) and Australian high(AH), Somali jet(SJ), STW. Otherwise, when the temperature of the NH is colder, the amount of cross-equatorial atmospheric heat transport(AHTEQ) to the north would increase, to compensate for the heat loss from the NH. And the ASM have been impacted by heating effects of the(AHTEQ) from the SH. So the geological records in the Asian monsoon region response to the signal of the temperature change in the SH to a certain extent. The thermal state of the western Pacific warm pool(WPWP) and the convective activities can affect the precipitation of the ASM by controlling the location and intensity of the Northwest Pacific subtropical high. When the Northwest Pacific subtropical high move to northward, the EASM enhanced, and the rain is pushed to the north; conversely, the EASM weakened, and the rain retreat south.