早在1926年,Allison[1]就报道了美国宾州Bear's Cave石笋的层状生长特征;1960年,Broecker等[2]报道了美国加州Moaning Cave 一个覆盖了人类股骨的钙华,该样品有1206个可识别的和200个被掩盖的环状韵律层,经放射性碳同位素定年,被认为这些韵律层为年层,可能反映了沉积方式的季节性变化;1993年,Baker等[3]通过微层计数与铀-钍定年,发现二者在误差范围内一致,首次验证了英国石笋荧光微层是年纹层,其发光强度可能与太阳黑子周期有关,并指出显微发光层可能是由上覆土壤的腐殖酸和富里酸的激发引起的.

The North Atlantic jet stream (NAJ) has a profound impact on the climate of the North Atlantic-European sector, especially in winter. Observations show that the winter NAJ (NAJw) has strengthened over the past similar to 140 yr. However, it remains unclear whether this long-term trend has deviated from the natural variability. Here, we present a 2500-yr-long reconstruction of NAJw strength using high-quality stalagmite delta 18O records from southeastern Europe. Our results show that the NAJw weakened during both the Roman Warm Period (300 B.C.- A.D. 200) and the Medieval Warm Period (A.D. 900-1250) but that it has strengthened under anthropogenic warming (since A.D. 1850). This indicates that its current trend has already deviated from the natural variability. The best explanation for this present anomalous trend of NAJw strength is that it was triggered by the appearance of the North Atlantic warming hole under anthropogenic forcing. This anomalous trend suggests that continued global warming may further strengthen the NAJw in the future.

Studies have shown that East Asia experienced several abrupt centennial‐scale weak monsoonal events in the early Holocene. However, the timing and structure of these climate events remain unclear due to the lack of precisely dated and highly resolved records. In this study, we present a well‐dated high‐resolution East Asia summer monsoon record from 11.32 to 10 ka BP based on two coeval stalagmites, one of which developed clear annual lamina, from Shihua Cave, northern China. Stalagmite δ 18 O records show 2 weak summer monsoon events at 10.9 and 10.3 ka. The 10.9‐ka event occurred from 10.93 to 10.79 ka BP for ∼140 years and features a “W”‐shaped structure. The 10.3‐ka event, also known as the ice‐rafted debris event 7 in the North Atlantic, lasted ∼260 years with an asymmetric double‐plunging structure. The two events are concurrent with the cold conditions in Greenland ice core record, indicating a close correlation between East Asia summer monsoon and North Atlantic climate. Spectral analyses on Shihua Cave stalagmite δ 18 O time series and annually lamina thickness sequence both show a statistically significant periodicity of 200 years, indicating that anomalous climate events may be triggered by solar activity. The 10.3‐ka event also coincides with three small freshwater outbursts in the high‐latitude North Atlantic. This agreement suggests that freshwater outbursts may have played a role in reinforcing this weak 10.3‐ka event in monsoonal China.

We developed a stable oxygen isotope chronology of tree-ring alpha cellulose (delta O-18(TR)) from archaeological teak (Tectona grandis L.f.) samples from Mae Hong Son (MHS) province, northwestern Thailand. The samples were collected from ancient coffins belonging to the log coffin culture excavated at the Ban Rai rock shelter (BR). The chronology spans a period of 283 years in the late Holocene (AD14-296). The oxygen isotopic composition of BR delta O-18(TR) ranged from 21.15 parts per thousand to 26.31 parts per thousand. Since delta O-18(TR) variations in Thailand teak can be used as indicators for precipitation amount during the rainy summer monsoon season, our chronology can be used as a proxy for regional late Holocene hydroclimate variability. This is confirmed by a significant positive correlation of our BR delta O-18(TR) record with a stalagmite delta O-18 record from Klang cave, southern Thailand (r = 0.303, p < 0.01). In addition, a REDFIT spectral analysis revealed the existence of multidecadal (26.9-year) and interannual (5.6, 3.4 and 2.8-year) cycles, which may potentially be the fingerprints of climate forcing mechanisms impacting Thailand monsoon precipitation, such as the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO).

Understanding the variability of the mid-Holocene climate on multi-decadal to centennial scales, including the well-known 5.5 kyr B.P. cold event, is important to better evaluate possible changes of the East Asian Summer Monsoon (EASM) as global warming progresses. Over the past few decades, stalagmite oxygen isotope records have been widely used as a proxy for the EASM; however, most high-resolution stalagmite records are from southern China. In this study, a 4-yr-resolution δ18O record obtained from stalagmite TW704 in northeastern China was used to reconstruct regional precipitation and the EASM between 5.82 and 4.77 kyr B.P. (where B.P. indicates “before 1950 A.D.”). In general, the inferred EASM variations agree with previously published stalagmite records from southwestern and central China, suggesting synchronous variations of the EASM on decadal to centennial scales across monsoonal China. Our new record also features relatively large decadal–centennial EASM oscillations from northern China, with two centennial-scale weak EASM events centred at 5.6 and 5.0 kyr B.P. The former corresponds to the well-known 5.5 kyr B.P. cold event that occurred in the high-latitude North Atlantic Ocean. These depressed EASM events were probably caused by prolonged periods of El Niño, resulting in decreased precipitation over northeastern China. Our study provides robust evidence to support the hypothesis that ENSO played an important role in modulating the EASM during the mid-Holocene.

The past climate in northwestern Thailand remains insufficiently understood because of the limitation of climate proxies. We present a new record of paleoclimate activity during 2050–1551 years BP (before the present), based on the analysis of the oxygen isotope ratios (δ18O) of tree-ring cellulose in ancient teak log coffins excavated from Namjang Cave in Mae Hong Son Province, northwestern Thailand. The ages of the teak log coffin samples were determined using C-14 dating. The average CoffinNJ δ18O value was 23.48 ± 0.77‰, values ranging from 21.23 to 25.42‰. The mean May–October (MO) rainfall reconstructed from the CoffinNJ δ18O data was 274 mm. The mean May–October (MO) rainfall data showed significant negative correlations with stalagmite δ18O data from Laos (r = − 0.254, p < 0.01), highlighting the existence of a weak monsoon from 291 to 294 AD and strong monsoon in 132 AD and 142 AD. Additionally, the MO rainfall data showed a significant positive correlation with reconstructed rainfall in Tibet (r = 0.347, p < 0.01). Spectral analysis of the CoffinNJ δ18O values revealed centennial cycles related to the sunspot number. The CoffinNJ δ18O values have a positive significant correlation with the sunspot number (r = 0.410, p < 0.01) over the entire period. Moreover, we found a highly significant positive correlation (r = 0.644, p < 0.01) between the CoffinNJ δ18O values and stalagmite δ18O values from Wanxiang Cave, China, and this correlation is related variations in the Asian monsoon. We conclude that the CoffinNJ δ18O data reflect the Asian monsoon from 2000 years ago and have the potential to be a paleoclimate proxy in northwestern Thailand.

Ancient teak log coffins found in Namjang (NJ) Cave, Pang Ma Pha district of Mae Hong Son province in Northwestern (NW) Thailand, were dated using a combination of C-14 dating and cross-dating techniques. The longest tree-ring width chronology (i.e., the CoffinNJ index) in Thailand covered a 477-year period from 106 BC to AD 371. The ages of the NJ log coffins fell within the log coffin culture epoch in NW Thailand. The NJ coffins are considered to belong to the second component of the log coffin culture period in NW Thailand, which began from approximately 2100 BP to 1200 BP. Spectral analysis of the CoffinNJ index displayed a decadal periodicity of 11.2 years, similar to the well-known 11-year periodic change in the sunspot cycle. A positive relationship (r = 0.31, p < 0.035) was observed between the CoffinNJ index and sunspot number for the entire period from 110 BC to AD 370, particularly during the period of AD 191–370 (r = 0.48, p < 0.045). Comparisons with speleothem proxies sensitive to changes in solar activity showed relationships between the CoffinNJ index and speleothem parameters (layer thickness: r = − 0.50, p < 0.001 and δ18O: r = 0.40, p < 0.001). The results confirmed that the ancient teak trees in this study might have responded, at least partly, to solar variation. The ring widths of the teak log coffins proved to be a promising proxy for studying the evolution of coffin culture and past climate change in this area.

Thailand is situated in a transition zone of overlap between the Indian monsoon (IM) and the western North Pacific (WNP) monsoon. The region serves as an important area to study the influences of different moisture sources. This study presents the first stable oxygen isotope analysis on seven teak (Tectona grandis Linn.) trees collected from Phrae Province in northern Thailand at different temporal resolutions. Isotopic analyses of teak tree rings at both annual and sub-annual timescales reflected the variations in their source water oxygen isotope ratios (delta O-18, i.e., rainfall) to different degrees (Annual scale: r= 0.31, p < 0.05, Monthly scale: r= 0.63, p < 0.01). A 146-year-long annually resolved tree-ring cellulose delta O-18 series, spanning between AD 1871 and 2016, exhibited moderate negative relationships with both local (r=-0.58, p < 0.01) and regional rainfall amounts, representing the climatology of rainfall totals during the entire summer monsoon period from May to October. A spatial correlation analysis between monthly resolved tree-ring cellulose delta O-18 with large-scale Climate Prediction Center (CPC), Outgoing Longwave Radiation (OLR), and Merged Analysis of Precipitation (CMAP) datasets, as well as an air mass backward trajectory analysis, indicated that the intraseasonal tree-ring cellulose delta O-18 values reflected changes in moisture originating from the Indian and Pacific Oceans, rather than the amount of local precipitation. These results imply that variations in northern Thai teak cellulose delta O-18 values are modulated not only by the local rainfall amount but also by large-scale convection, which varies between different seasons and over time. Advance knowledge of the regional monsoons in the transition area can therefore lead to a broad and complete understanding of the entire Asian monsoon circulation.

本研究利用辽宁本溪庙洞石笋MD12,通过230Th定年和高分辨率氧同位素分析,并集成庙洞另一支石笋MD11序列,重建了3.04～2.60ka B.P.时期辽东地区夏季风(降水)变化历史.该石笋氧同位素序列记录了2.8ka事件的详细过程,事件的核心阶段起止时间约为2.76～ 2.66 ka B.P.,中心点位于2.68 ka B.P.,稍微晚于西南石笋氧同位素记录(约2.71 ka B.P.),但是在事件的开始时间上,庙洞石笋氧同位素记录比西南石笋氧同位素记录晚了约100年.因此,庙洞石笋氧同位素记录与西南石笋氧同位素记录中显示的缓慢减弱-快速增强模式不同,2.8ka事件在辽东石笋氧同位素记录中表现为快速减弱-突然增强的变化模式,与太阳活动代用指标一致变化,支持太阳活动是2.8ka弱季风事件驱动因子的观点.庙洞石笋氧同位素快速响应太阳活动的变化特征,说明其动力学机制可能是太阳活动减弱导致北半球高纬度地区温度降低,然后通过大气“遥相关”作用影响东亚夏季风.

Thailand monsoon is located in the transition zone between the Indian and western North Pacific monsoons. Assuredly, proxy climate data from this area could improve our understanding of the nature of Asian monsoon. Tree rings and stalagmites from this area are two potential materials for high-resolution paleoclimate reconstructions. However, a comprehensive understanding of these multiproxy records is still a challenge. In this study, a 76-year tree ring cellulose oxygen isotope value (δ 18 O) of a teak tree from northwestern Thailand was developed to test its climatic significance and potential for multiproxy climate reconstruction. The results indicate that the interannual variability of cellulose δ 18 O can be interpreted as a proxy of rainfall in the early monsoon season (May to July rainfall) as well as a proxy of relative humidity. Comparisons with speleothem proxies from the same locality and tree ring records from wider geographical areas provide a basis for developing a multiproxy approach. The results from a teleconnection analysis reveal that the El Niño-Southern Oscillation (ENSO) is an important climate mode that impacts monsoon rainfall in Thailand. High-quality proxy records covering recent decades are critically important not only to improve proxy data calibrations but also to provide a better understanding of teleconnections within the modern atmosphere. Preliminary findings demonstrated the potential of tree ring stable isotopes from Thai teak to develop multiproxy climate reconstruction.

Much attention has been paid to the variability in East Asian Summer Monsoon(EASM)during the first few thousand years of late Holocene,due to its potential connection with Chinese civilization development.In this study,a stalagmite MD11 from the Miaodong cave,Benxi,Liaoning province has been employed to reconstruct a high resolution δ18O record during time period between 4.09 ka BP and 2.84 ka BP.The variability in MD11 δ18O is explained to be a proxy index of EASM and(or)local summer monsoon precipitation,with more negative value indicating stronger EASM or more summer precipitation.During 4.09-3.85 ka BP,the EASM was relatively stable,similar to some stalagmite records from southern China,indicating that the well known "4.2 ka" cold event(failure EASM)maybe occurred at least earlier than 4.1 ka BP.In general term,δ18O value is much less negative from 3.85 ka BP until 2.84 ka BP.This observation is together with much lower deposition rate,revealing a long term weakening of EASM.It should be known that a short term(several decades)rebound in intensity of EASM occurred at around 3.05 ka BP.Our observation coincides with that of history document that weak EASM and drought in northern China dominate the time period of 4-3 ka BP.

基于辽宁本溪庙洞降水和滴水的氢氧同位素,以及滴水碳酸钙沉积的氧同位素两年的观测数据(2012～2013年),本文分析了庙洞滴水氧同位素对大气降水氧同位素的继承性,分析并讨论了洞穴滴水碳酸钙沉积的氧同位素时空变化特征、影响因素及其对石笋古气候重建的指示意义.结果表明:1)庙洞降水δ18Op季节性特征明显,冬季降雪最负(-13.43‰),6～9月降雨次之(-9.82‰),而春秋季降雨最正,当地降水线:δD=7.28δ18O+7.10(n=21,r=0.97),与东北地区大气降水线平行,但过剩氘更大;斜率小于全球大气降水,与北京石花洞结果更接近.2)庙洞3个观测点的滴水δ18Ow在误差范围内基本相同(约-9.6‰),常年稳定,年际变化微弱(0.2‰),值介于全年降水加权平均值(-9.81‰)与4～ 10月降雨加权平均值(-9.56‰)之间,更接近于后者,滴水的δD-δ18Ow位于降雨线性回归线的平均位置,与降雪的δD-δ18O回归线明显不同,说明滴水更多记录降雨的平均值,而降雪贡献较小.3)滴水碳酸钙沉积的氧同位素出现显著的空间差异,滴水较快的点,其δ18Oc没有明显的季节变化;相反,滴水慢的点,则出现明显的季节性变化(变幅约为0.4‰),其δ18Oc值相对于滴水快的点整体偏正约0.26‰,这种时空差异可能是由滴率太慢引起的动力分馏造成的,其机制可能与蒸发作用增强和(或)CO2逸出比例增大有关.这种动力分馏机制可能是一些相同时段石笋氧同位素出现系统偏差的潜在原因.4)滴水沉积的δ18O.值较理论计算值δ18Oct偏正,即使是无明显动力分馏的点也相差约0.59‰,这与最近一些室内模拟实验结果类似,暗示洞穴滴水氧同位素分馏系数较常规经验值(1.0313)略大.

早在1960年,Broecker等[1]首次报道了洞穴碳酸钙年轮;而后Baker等[2]通过230Th定年和微层计数对比,证明了1根来自苏格兰的石笋SU-80-11的发光微层为年层.在我国,刘东生等[3]首次在北京石花洞发现了石笋微层,并确定为年层[4].自此,石笋微层引起了国内外专家的关注并被广泛用于高分辨率古气候重建[5,6],包括建立层厚年表[7]、建立精确的年龄-深度模型,用以确定气候/地质事件转换和持续的精确时间[8～11]等.但是,石笋微层中存在的年层缺失和伪年层问题一直是阻碍石笋微层广泛运用的关键因素.