Paleoclimate Change From 26.5kaB.P. To 24.1kaB.P. In Chongqing Area Based On High Resolution SM1 Stalagmite Record

We have attempted to collect stalagmites in caves around Chongqing for paleoclimate reconstructions over the past a few years. These caves include Liangtianwan (LT), Furong (FR), Xueyu (XYD), Shuiming (SM) and Xinyan (XY) Caves are located in the karst region of southeastern Chongqing and represent largely the depositional conditions of cave speleothems in the area. Here we discuss the SM1 stalagmite collected from Shuiming Cave, Fengdu, Chongqing. A time scale of the sample SM1 has been reconstructed by a polynomial fitting with 7 dated ages. It deposited from 26.5kaB.P. to 24.1kaB.P. in a fast growth rate. On the basis of a high resolution (equivalent to a resolution of 20 years on average.) δ¹⁸O record of SM1 stalagmite, we divided this time scale into 3 stage: ? 26.5²6.01 ka B.P.: Highly negative values of δ¹⁸O correspond to the strong summermonsoon in this stage. The average δ ¹⁸O value is -8.650%o, and the lowest value reaches-8.836‰.It shows that the whole area was controlled by north pacific sub-tropic high insummer. â‘¡ 26.01-24.60lka B.P.: The δ¹⁸O value shifted to a positive level very quickly, and fluctuatedduring -8.492%o to -7.901‰.It revealed that cooler temperature and more precipitation inChongqing caused by a weaker summer monsoon. (3) 24.601²4.104ka B.P.: The δ¹⁸O value shifted positively very rapidly, and on the contrast the813C value shifted negatively. The SMI stalagmite shows the H2 event in Chongqing in the global paleoclimate change, whereas it was wet in Chongqing contrast to the dry trend globally.Generally speaking in the whole stage, the 5I8O value changed from lower to higher, and the temperature change from higher to lower. Heinrich event 2 was recorded in 24.601ka B.P..With the current age data and stable isotope profiles, here we compare SMI with other stalagmites collected from Chongqing. In summary, our observations from the preliminary results include: (1) abundant and fast growth of the stalagmites during glacial intervals in the area;(2) when deposition of the stalagmite changes, its 518O value also changes, with light 818O values corresponding to relatively pure (white) calcite deposit and heavy 818O values to impure (dark) calcites.Numerous previous studies in China found that slow or no stalagmite growth during glacial intervals due to strongly cold and dry climates, and fast growth of stalagmites during interglacials under warm and wet summer monsoons especially in northern China. However, we find that the growth of stalagmites in Chongqing area was significantly abundant and fast during glacial intervals. Our hypothesis on this phenomenon is that the monsoon boundary in China was shifted southeastward during glacials and the rainy frontal zone was probably above the area of Chongqing area. On the other hand, the cooling temperature was not cold enough to generate mountain glaciers to cover the surface above the caves. Therefore, higher CaCO3 saturation under cooler temperature and continuous flow of cave drip water would make the stalagmites to grow intensively.