Summer monsoon precipitation variability during recent 700 years recorded in a high-resolution stalagmite from Southwestern Yunnan, China

High-resolution and precisely dated climate records are necessary for further investigating the climate variability during the Little Ice Age(LIA). Here, we present a high-resolution oxygen isotope(δ¹⁸O) time series from Sigangli Cave to characterize the climate changes during the LIA. Sigangli Cave(23°32'N, 99°33'E; 1200 m a.s.l.) is located in Cangyuan County, southwestern Yunnan, China. Regional climate of the cave is dominated by Indian summer monsoon(ISM) with moistures mainly coming from the Bay of Bengal. Mean annual temperature and precipitation in this region recorded by Cangyuan Meteorological Station are 17.7℃ and 1750 mm(1981~2010 A.D.), respectively. Most of the precipitation(about 87%) occurs during the summer monsoon season from May to October. Stalagmite SGL1 was collected in the innermost chamber of the cave with 168 mm in height and 60 mm in diameter. It is composed of gray-white, densely crystallized pure calcite. A clear hiatus was observed on the polished surface at 35~36 mm from the top. Total of 7²³⁰Th dating were performed on MC-ICPMS. Totally 350 subsamples for stable isotope measurements were drilled(325 along the vertical growth axle and 25 along horizontal layer at 5 depths for "Hendy Test"), and analyzed with MAT 253 coupling with Gasbench-Ⅱ. The SGL1 δ¹⁸O time sequence with an average resolution of 2 years covers the intervals of 1322~1605 A.D. and 1700~1927 A.D. Its variabilities are interpreted as the variation of regional monsoon precipitation. The SGL1δ¹⁸O values vary from -9.16 ‰ to -6.84 ‰, with an average value of -8.01 ‰, and exhibit centennial-scale fluctuations with increasing values from 1322 A.D. to 1605 A.D. and from 1700 A.D. to 1927 A.D., indicating the persistently decreasing trends in summer monsoon precipitation. These decreasing trends inferred from SGL1 broadly coincide with other stalagmite records from ISM region within the limitation of dating error. However, the increasing trend during interval of 1700~1927 A.D. was observed in some cave records from East Asian summer monsoon(EASM) region. The existence of inconsistent monsoon precipitation behaviors in Asian monsoon region on centennial scale reveals the complexity of monsoonal climate variation during the LIA. The most prominent feature of the SGL1 sequence is a series of decadal-scale oscillations punctuating on long-term trend. There are nine drought events(numbered W1~W9) with the duration of 10~20 years and average amplitude of 1.4 ‰ can be identified during 1322~1540 A.D., in which the time resolution of δ¹⁸O sequence is up to 1~2 years. These drought events coincide well with drought events logged in tree-ring based Palmer Drought Severity Index (PDSI) record from southern Vietnam. Within them, drought event W1~W2 and W3~W4 correspond to so called Angkor Ⅰ and Ⅱ Drought, respectively, the later was suggested as a key factor to explain the demise of Angkor Period. A more remarkable drought event, with an amplitude of 2.1 ‰ in δ¹⁸O, was identified in the interval of 1730~1820 A.D. This decadal-scale drought events were also recorded in other climate records from Asian monsoon region. The SGL1δ¹⁸O sequence is positively correlated with the total solar irradiance(TSI) on multi-centennial scale, suggesting that solar activity plays an important influence on monsoon precipitation in southwestern Yunnan through the LIA. During the interval of 1322~1540 A.D. with well dating and high resolution, our record agrees with index of Pacific Decadal Oscillation(PDO) and is similar in part with Atlantic Multi-decadal Oscillation(AMO). Most of the drought events during this time periods are corresponded to warm phases of PDO, indicates that PDO plays importance role on climate on decadal scale in study region. Spectral analysis results show significant cycles of 15, 24 and 56 years, which are similar with dominant periodicities of PDO, further supporting the PDO impact. Statistically significant periodicities of 2.6~3.2 and 6 years had also been identified, hinting influence of EI Niño-Southern Oscillation(ENSO) and/or Indian Ocean Dipole(IOD), on sub-annually scale climate in this region.