從越南北部高解析度之石筍紀錄探討三萬至二萬二千年前的亞洲夏季季風變化

Abstract

Northern Vietnam is an ideal place to address the influence of Asian summer monsoon (ASM) or Indian Ocean monsoon (IOM) in the Indo-China Peninsula area. Besides, speleothem is an excellent material of terrestrial climate proxy due to continuous growth over thousands of years in different regions and can be dated precisely by U-Th dating. Twenty-two 230Th ages and 506 δ18O data were obtained from a stalagmite 2.9-3. The chronology is from 22.87±0.07 ka in the top to 30.21±0.12 ka in the bottom with the best precision as 62 years, but one hiatus was found in 27.8-25.4 ka. This study followed Wang et al. (2001) thought and attributed the δ18O decreasing to the amount effect of summer precipitation. Two implied strong ASM periods from 30.21 ka to 27.77 ka were temporally consistent and isotopically comparable with the Hulu record, which confirmed the north Indo-China Peninsula was mainly influenced by ASM. This study thus supported the synchronicity of millennial events all over the world. However, millennial events were punctuated by hundreds-of-year episodes and it left the debatable and unsolved questions for existing and timing of centennial-scale events. Comparing the 2.9-3 record to the Greenland ice core record, three discrepancies were presented. First, the onset of the strong ASM in 30.18-28.47 ka led the GIS 4 warming event about 1.28 ± 0.9 ka. Second, the duration of 1.71 kyrs for the ASM is longer than that of 0.5-0.6 kyrs for GIS4. Third, the symmetry-type strong ASM episode contrasted to the see-saw-type millennial event in the north Atlantic. Lastly based on the spatial comparisons and the oxygen isotope features, the hypothesis was preferred that changes in the dynamics of the tropical atmosphere-ocean system resulted in the cyclic millennial events.