基于河套盆地HJ01钻孔已有年代框架,对湖相沉积物中207个样品进行了孢粉分析,并利用加权平均偏最小二乘回归(WAPLS)方法定量重建了河套盆地~68.6—46.4 ka BP的最暖月气温变化过程。结果表明:(1)河套盆地内植被类型以荒漠草原为主,主要...基于河套盆地HJ01钻孔已有年代框架,对湖相沉积物中207个样品进行了孢粉分析,并利用加权平均偏最小二乘回归(WAPLS)方法定量重建了河套盆地~68.6—46.4 ka BP的最暖月气温变化过程。结果表明:(1)河套盆地内植被类型以荒漠草原为主,主要科属含量在不同阶段存在差异;周围山地发育以云杉为主的针叶林,经历了2期扩张和1期退缩。(2)~68.6—57.0 ka BP最暖月气温为14.2℃,在10.1~16.9℃之间波动,表明气候整体寒冷;~57.0—52.2 ka BP最暖月气温平均升高1.5℃,最高时可达15.7℃,并在10.5~21.6℃之间波动,表明气候转暖;~52.2—46.4 ka BP最暖月气温为15.8℃,在13.2~17.8℃之间波动,表明气候相对温暖。(3)重建最暖月气温与全球典型古气候记录对比显示,北半球夏季太阳辐射及欧亚冰量的变化可能是影响河套盆地~68.6—46.4 ka BP最暖月气温变化的重要驱动因素。研究结果可为预测未来冰期气候变化提供科学参考。展开更多
A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3―26 cm interval determi...A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3―26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ 18O and δ 13C, mostly in the 2.3―26 cm part. The δ 18O and δ 13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial in-terval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ 18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ 18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ 18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ 18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ 18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high fre-quency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology. The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having climatic significance.展开更多
文摘基于河套盆地HJ01钻孔已有年代框架,对湖相沉积物中207个样品进行了孢粉分析,并利用加权平均偏最小二乘回归(WAPLS)方法定量重建了河套盆地~68.6—46.4 ka BP的最暖月气温变化过程。结果表明:(1)河套盆地内植被类型以荒漠草原为主,主要科属含量在不同阶段存在差异;周围山地发育以云杉为主的针叶林,经历了2期扩张和1期退缩。(2)~68.6—57.0 ka BP最暖月气温为14.2℃,在10.1~16.9℃之间波动,表明气候整体寒冷;~57.0—52.2 ka BP最暖月气温平均升高1.5℃,最高时可达15.7℃,并在10.5~21.6℃之间波动,表明气候转暖;~52.2—46.4 ka BP最暖月气温为15.8℃,在13.2~17.8℃之间波动,表明气候相对温暖。(3)重建最暖月气温与全球典型古气候记录对比显示,北半球夏季太阳辐射及欧亚冰量的变化可能是影响河套盆地~68.6—46.4 ka BP最暖月气温变化的重要驱动因素。研究结果可为预测未来冰期气候变化提供科学参考。
基金the National Natural Science Foundation of China (Grant Nos. 40672165, 90511004, 40672202)the Academician Special Project of Chongqing Science Committee (Grant No. 2003-7835)
文摘A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3―26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ 18O and δ 13C, mostly in the 2.3―26 cm part. The δ 18O and δ 13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial in-terval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ 18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ 18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ 18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ 18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ 18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high fre-quency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology. The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having climatic significance.
