Study On The Evolution Of Southwest Monsoon In 13.2 ~ 2.6ka BP

As an irreplaceable component of global change, Asian monsoon plays a significant role in global moisture cycle and energy transmission. Stalagmites records from low-latitude region have made a huge contribution to paleoclimatic field. Here we present one stalagmite collected from Chengjiachun Cave, southwestern Guizhou province. Based on7U/Th dates, some countable laminations and2459oxygen isotope data, a time series of Indian summer monsoon variability from13.2to2.6ka BP is reconstructed. The amplitude of this stalagmite δ18O records can reach about6%o, which means that this stalagmite δ18O records could response to outside climatic change sensitively.The long-term trend of the Chengjiachun cave δ18O record obeys to the summer insolation at25°latitude. By comparing our records to East Asian monsoon records, and North American monsoon records, we find their behaviors are the same on millennial-centennial scales. Therefore, the variability of the low-latitude monsoon may be controlled by the position of ITCZ, the evolution of Asian monsoon is a global system.Under different climatic boundary conditions, the controlling factors of Indian monsoon intensity are not all the same. Our record shows a broad similarity to the δ18O record of Greenland Ice during the early Holocene, it reveals that early Holocene monsoon intensity is mainly controlled by glacial boundary conditions. However, during mid-to late Holocene, Indian monsoon intensity decreases gradually in response to summer solar insolation.The "5.6ka" event shows a "W" type of internal structure, with duration of185a. By comparing with solar activity and utilizing spectral analysis, indicating that decreasing of solar activity is the cause of "5.6ka event", but other factors such as the strength of ENSO may also affect the intensity of monsoon on several-decades scale. The "4.5ka" event presents a "two-peak and triple-valley" pattern, which is primarily affected by North Atlantic climate, demonstrating that the climatic teleconnections between low-latitude and North high-latitude are also present in mid-to late Holocene.