Abrupt Holocene changes of the Asian monsoon at millennial- and centennial-scales: Evidence from lake sediment document in Minqin Basin, NW China

Considerable research is now focusing on abrupt Holocene changes at millennial- and centennial-scales all over the world. This study shows that the changes in the Holocene summer monsoon can be divided into two main periods, based on climatic proxy records of lake sediments from the Sanjiaocheng section located at the NW boundary of the summer monsoon, Gansu Province. The early and middle Holocene was humid with stronger summer monsoon, while the late Holocene is dry with weak summer monsoon. Detailed results also show a series of millennial- and centennial-scale changes in the intensity of the summer monsoon, with a periodicity of {dy1600} years during the whole Holocene, and with a periodicity of 800 years during the early Holocene. Ten dry events during the Holocene are associated with the weakening of the summer monsoon. These rapid climatic changes may be representative of a global climatic change pattern during the Holocene.     

Evidence of a humid mid-Holocene in the western part of Chinese Loess Plateau

Field works show that the wetland/swamp layers were distributed ubiquitously in the western part of the Chinese Loess Plateau. Universality of the wetland/swampy layer and the consistency of the age reveal that the layer was developed under the humid climatic condition. Dated between 9 and 3.8 kaBP, the wetland/swampy layer is full of aquatic mollusks and has the highest tree and shrub pollen,indicating a humid mid-Holocene. Variations of grain size suggest that winter monsoon weakened during 9-3.8 kaBP while climate change to humid and vegetation cover increased from 9 kaBP onward. After 5.9 kaBP, the humidity declined gradually. In 3.8 kaBP, summer monsoon sharply retreated, and the climate changed to dry.     

Palaeoclimate simulation of Little Ice Age

Promotedbytheinternationalresearch projectsofPAGESandCLIVAR ,thestudiesonclimaticandenvironmentalchangesinthepast 2 0 0 0yearshavedrawntheattentionofgeologistsandpalaeoclimato logistsallovertheworld[1,2 ] .AmongthemthecoldeventoftheLittleIceAge (LIA)isparticularlythemostattractiveone[3～ 10 ] ,whichisthenearesttypicalcoldperiodintheglobalrangefrommodernage ,andhadaprofoundimpactuponhumansociety[11] .Addi tionally ,moreknowledgeaboutthecauseoforiginanddynamicmechanismofLIAmayenrichandpe…     

Vegetation evolution and its response to climatic change during 3.15–0.67 Ma in deep-sea pollen record from northern South China Sea

In order to study vegetation evolution and environmental change during 3.15-0.67 Ma,a total of 608 pollen samples with an average time resolution of 4 ka has been analyzed from ODP Site 1145(water depth 3175 m),northern South China Sea.The deep-sea sediments(213.62-91.9 m) cover from 3.15 to 0.67 Ma based on micropaleonotological stratigraphy.The characteristic features of the pollen diagram include that,pollen influx rises twice obviously around 2.58 Ma and during 2.0-1.8 Ma,in response to global climatic cooling and winter monsoon enhancement.Before 2.58 Ma,tropical and subtropical vegetation,mainly evergreen Quercus(E) and Altingia,predominated around northern SCS with much more tropical montane conifers and ferns relatively.From 2.58 Ma,temperate vegetation increased obviously,implying climatic cooling and winter monsoon enhancement.Spectral analysis shows that percentage variation in tropical and subtropical taxa has a strong 20 ka procession cycle probably due to the summer monsoon;while pollen influx has 100,41 and 19 ka cycles,indicating the sea level and winter monsoon change response to the ice-sheet variations.     

贵州荔波42.0kaB.P.~65.0kaB.P.气候变化的石笋记录

对贵州荔波董哥洞D42石笋进行TIMS-U测年和碳、氧同位素分析,建立末次冰期42．0ka B．P．～65．0ka B．P．的古气候变化时间序列。研究结果表明,荔波地区在65．0ka B．P．～42．0ka B．P．石笋记录的冷暖事件所反映出的季风气候变化,大致可分为3个气候阶段;65．0ka B．P．～60．6ka B．P．相当于海洋氧同位素MIS4晚期,反映本阶段东亚冬季风强盛,气温降低,表现为干旱寒冷的气候环境;60．6ka B．P．～48．4ka B．P．相当于海洋氧同位素MIS3早期,反映东亚夏季风相对增强,气温升高,有效降水相对较少,表现为温暖半干旱的气候环境;48．4ka B．P．～42．0ka B．P．相当于海洋氧同位素MIS3中期,显示东亚夏季风由强变弱,东亚冬季风相对增强,表现为干旱冷凉的气候环境。石笋记录揭示的2次寒冷事件在各类沉积物中均有记录,反映为全球变化的气候事件,相当于北大西洋沉积物中的Heinrich5和Heinrich 6冷事件,可以进行全球对比,显示荔波地区与北极地区存在着古气候的遥相关。     

A continuous 3000—year precipitation record of ENSO variability during LGM from a stalagmite in Nanjing

A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar years before the present (aBP) was analyzed for evidence of East Asian summer monsoon precipitation variability during the Last Glacial Maximum (LGM). Power spectral analysis of the sequence shows a distinct interannual (2—7 years) band of enhanced variability suggestive of El Ni駉-Southern Oscillation (ENSO) teleconnections into East China during the LGM when climatic boundary conditions were different from those of today. The lower frequency bands (4—7 years) variability becomes weaker from 18179 to 14900 aBP, sup-porting the precession forcing model. The reappearance of the ENSO band in the coldest climatic boundary conditions during the Heinrich Event 1, however, suggests the stimula-tion of the enhanced East Asia winter monsoon to the El Ni駉 events.     

Influence of the intertropical convergence zone on the East Asian monsoon

The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the B?lling-Aller?d warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.     

冻土退化过程中植被覆盖度的变化研究

在全球气候变暖的背景下,青藏高原的多年冻土出现了不断退化的现象.退化的多年冻土隔水作用减弱或消失,并导致依赖于冻结层上水的植被变化.在模拟高原多年冻土分布的基础上,分析了冻土的退化过程植被覆盖度的变化,结果表明,冻土的变化可分为3个阶段:冻土稳定段(80年代)、冻土快速退化段(90年代)和冻土缓慢退化段(最近十几年).同时,采用GIMMS(global inventory modeling and mapping studies)第3代NDVI数据(1982—2012年)分析青藏高原植被覆盖度的斜率变化特征,结果显示:在近31a来,青藏高原的植被覆盖度斜率整体上呈微弱增加趋势;植被覆盖在冻土退化的3个时段内的变化特征为:从20世纪80年代冻土相对稳定期到90年代的冻土退化期,比退化面积增大11%;近十几年来,冻土退化逐步减缓,植被退化的增幅减弱,面积比90年代增大了3%,但退化的区域更为集中.冻土退化与植被的变化机制复杂,本文的分析与发现对理解冻土对生态的影响有一定的意义.     

Long-term trend and abrupt events of the Holocene Asian monsoon inferred from a stalagmite δ18O record from Shennongjia in Central China

The middle-Holocene was a period of profound cul- ture transitions: the Neolithic culture around Central China[1], Mesopotamia[2] and India[3] all mysteriously collapsed around 4 ka . It is plausible that this civiliza-tion collapse can be contributed to …     

Millennial-scale climate change since the last glaciation recorded by grain sizes of loess deposits on the northeastern Tibetan Plateau

Whether climatic changes in high latitudes of the Northern Hemisphere since the last glaciation have effects on the Tibetan Plateau monsoon, and the variation characteristics of the Plateau monsoon itself are still not solved but of great significance. The 22-m high-resolution Ioess-paleosol sequence in the Hezuo Basin on the northeastern Tibetan Plateau demonstrates that the Plateau winter monsoon experienced a millennial variation similar to high latitude Northern Hemisphere, with cold events clearly correlated with Heinrich events but less for the warm events (Dansgarrd-Oeschger events). It may indicate that the climate system at high latitudes in the Northern Hemisphere had played an important role in both the Plateau monsoon and the high-level westerlies. On 10^4 year scale, there are two distinct anomalous changes, which are not found in the records from high latitude northern hemisphere, revealed by the loess grain size in the Hezuo Basin. One is that there was a considerable grain size increase at -36 kaBP, suggesting an abrupt enhancement of the Plateau winter monsoon at that time; the other is that, during 43--36 kaBP, the grain size decreased distinctly, indicating a notable weakening of the Plateau winter monsoon around that period. Both of the two anomalies suggest that the Tibetan climate may have been controlled by some other factors, besides the high latitude climatic changes in the Northern Hemisphere.     

青藏高原冬季积雪异常对东、南亚夏季风影响的初步数值模拟研究

利用一个耦合了简化的简单生物圈模式的大气环流谱模式（ＳＳｉＢ－ＧＣＭ），初步探讨了青藏高原冬季积雪异常对东、南亚夏季风环流和降水的影响及其机理。结果表明，高原地区冬季积雪增加将使随后的夏季东、南亚季风明显减弱，主要表现为东、南亚季风区降水减少，索马里急流、印度季风槽和印度西南气流减弱。另外，还提出欧亚大陆雪盖与整个高原雪盖和高原东部雪盖对东、南亚夏季风影响的敏感性问题。与欧亚大陆雪盖相比，高原雪盖是影响东、南亚季风的更敏感区，冬季高原以外雪盖增加，有可能使亚洲季风增强；当高原东部雪盖增加时，高原以东地区及印支半岛降水减少，印度东部、南部和孟加拉湾西北部降水反而增加     

青藏高原：全球气候变化的驱动机与放大器──Ⅲ．青藏高原隆起对气候变化的影响

新生代出现的几次重大气候变化事件与青藏高原形成过程中经历的几次强烈构造运动在发生年代上的良好对应关系表明两者存在紧密的联系．或许正是青藏高原的隆起导致了气候的巨大变化和现代东亚季风的形成及加强．高大的高原对大气系统有两个重要影响，热力作用和动力作用．它们在亚洲冬季形成蒙古高压、夏季形成印度低压，从而导致东亚季风出现．青藏高原越高，其对大气的作用越显著，形成的蒙古高压、印度低压和东亚季风越强大．因此，东亚季风的形成和加强是青藏高原隆起的结果．东亚季风的加强和高原动力作用使西风带波动增加，造成冰期极地冷空气不断南侵、气候波动变大．青藏高原抬升和季风造成的化学风化增强还使大气ＣＯ２含量降低、气候变冷．因此，青藏高原隆起是控制新生代气候变化的重要因素．     

Record of environmental change by α-cellulose δ13C of sphagnum peat at Shennongjia, 4000―1000 aBP

The Dajiuhu Basin at Shennongjia, located within typical East Asian Monsoon region, preserves a sub-alpine sphagnum peat deposition in its central area. The topmost 120 cm of the peat covers the last 4000 years according to AMS ^14C dating of pollen concentration. Carbon isotope of a-cellulose, extracted from sphagnum peat, provides a quantitative reconstruction of atmospheric relative humidity, based on transfer functions of C3 plants carbon isotopic fractionation equation and the bryophyte photosynthesis CO2 absorption rate equation. δ^13C, TOC and C/N variations reveal that the Dajiuhu area has experienced a long-term tendency to dry during 4000-1000 aBP, with a major transition happening around 3000 aBP. Four relative dry events are identified at 3400-3200, 3000-2600, 2200-2000 and 1600-1400 aBP, respectively, corresponding to those climate events documented in many global records. Three periodicities, 664 a, 302 a and 277 a enclosed in the atmospheric humidity of Dajiuhu are correlated to the cycles of solar activities. The weakening of East Asia summer monsoon during this period registered in the Dajiuhu peat is consistent with the synchronous weakening of Indian Monsoon. This trend may be attributed to gradual decrease of Northern Hemispheric summer solar insolation and the consequently southward migration of Intertropical Convergent Zone （ITCZ）.     

华北夏季降水年代际变化与东亚夏季风、大气环流异常

利用华北夏季降水资料和NCEP/NCAR再分析资料,对华北夏季降水、东亚夏季风年代际变化特征及大气环流异常进行研究,发现一些有意义的结果:华北夏季降水变化存在明显的8a、18a周期,东亚夏季风变化18a、28a周期性比较明显,二者年代际变化特征明显,但华北夏季降水变化和东亚夏季风变化的周期不完全一致.华北夏季降水量变化在60年代中期发生了突变,东亚夏季风变化在70年代中期发生了突变.华北夏季降水与东亚夏季风变化存在很好的相关关系,强夏季风年,华北夏季降水一般偏多,弱夏季风年,华北夏季降水一般偏少,但又不完全一致.东亚夏季风减弱是造成华北夏季降水减少的一个重要因素,但不是唯一因素,华北夏季降水减少还与环流异常密切相关.在地面上,青臧高原地区、华北地区气温下降造成华北低压系统活动减少,不利于降水.在850 hPa层上,东亚中纬度的西南季风和副热带高压南部的偏东风、西北部的西南风异常减弱,使得西南气流输送水汽很多难以到达30°N以北的地区,而副热带高压西部外围偏东南、偏南气流输送到华北地区的水汽也大量减少,水汽不足造成华北夏季降水偏少.在500 hPa高度场上,80年代欧亚遥相关型表现与50年代相反,变为欧洲( )、乌拉尔山(-)、中亚( )形势,这种环流使得乌拉尔山高压脊减弱,贝加尔湖至青藏高原高空槽变浅,纬向环流表现突出,不利于冷暖空气南北交换.同时在500 hPa气温场上,80年代,西伯利亚至青藏高原西北部的冷槽明显东移南压到蒙古至华北地区,锋区位于华北以东以南位置,使得华北地区冷暖空气交汇减少,降水也因此减少.华北夏季降水减少是由于东亚夏季风减弱和大气环流异常造成的.     

Inverse correlation between ancient winter and summer monsoons in East Asia？

There is a scientific debate on the relationship between ancient winter and summer monsoons in East Asia. Some scholars think that East Asian winter and summer monsoons are anti-correlated, and others think not. For this reason, this study is motivated to assess their linkage from the paleoclimate simulation perspective, through analyzing the Last Glacial Maximum （LGM） and mid-Holocene （MH） climate simulated by CCSM3 model. Compared to the present climate, the Aleutian low is found to be deepened and the East Asian winter monsoon （EAWM） is stronger during the LGM winter. The Pacific high in summer is noticed to be weakened and the East Asian summer monsoon （EASM） is weaker at the LGM. During the MH, the Aleutian low and the Asian high in winter are intensified, and the Asian low and the Pacific high in summer are enhanced, indicating that the EAWM and EASM are both stronger than today. Therefore, the EAWM is not always negatively correlated to the EASM. Their relationship may be different at different geological stages. It can be obtained at least from the numerical simulation results that the EAWM and the EASM is negatively correlated during the cooling period, while positively correlated during the warming period.     

An ice-core record of vegetation and climate changes in the central Tibetan Plateau during the last 550 years

We present a 550-year ice-core pollen record with a 5-year resolution from the Puruogangri ice field in the central Tibetan Plateau.Analysis of the relationship between pollen record and instrumental observations suggests that the sum of the steppe and meadow pollen taxa is a good indicator of summer (June-August) temperature,whereas the ratios of Cyperaceae/(Gramineae+Artemisia) [Cy/(G+A)] as well as M/S (meadow to steppe percentages) are indicative of humidity changes in this region.Together with δ18O and...     

The summer monsoon evolution recorded by carbon isotope of organic matter from the Yuanbao loess section during the Last Interglaciation

Based on the carbon isotope record of organic matter from the Yuanbao loess section, northwestern China, five enhanced summer monsoon events were observed at this area during the Last Interglaciation. Such events were also recorded by the paleosol layers, pollen assemblage and magnetic susceptibility. It is suggested that the enhanced summer monsoon leads to the shift of vegetation type, which results in the change of δ¹³C value of organic matter in the paleosol layer. It appears that the δ¹³C of organic matter is a good indicator for the summer monsoon variation. Among these five events, the first, second and the fifth reached their maximum smoothly, but the other two had experienced a less cold stage before reaching their peaks, which suggests that the mechanisms of such events may be different.     

1990—2010年间我国北方农牧交错带植被覆盖度变化归因

以我国北方传统农牧交错带为研究区,以植被归一化指数(NDVI)表征地表植被覆盖度,对土地利用数据和降水量、气温等气象数据两大类影响因子进行相关性分析.研究发现:1990—2010年该地区主要土地利用类型发生了显著的相互转化,但占优势的仍是草地、耕地和林地,土地利用和景观结构未发生重大变化.研究期间,北方农牧交错带耕地、林地和未利用土地植被覆盖度均有所增加,草地植被覆盖度有所减少.植被覆盖度与年均降水量呈极显著相关性,1990—2010年农牧交错带降水呈减少趋势,植被覆盖度上升趋势明显.植被覆盖度与同期年均气温数据也呈现一定的正相关性,1990—2010年农牧交错带气温变化属于升温趋势,植被覆盖度上升趋势明显.研究表明北方农牧交错带植被覆盖度变化是在全球气候变化和人类活动的双重影响下发生的,土地利用变化和降水、气温气象数据两种因素对植被覆盖度的影响具有明显的地域性特征,土地利用变化因子的影响由于受政策和人类活动的参与而正逐渐占据着主导地位,而气候条件中,气温升高对植被覆盖度具有一定的正相关性,降水量因子在径流量充沛地区影响作用较弱,但在水源缺乏,人类活动干预较少农牧交错带西北地区仍然有着重要的影响作用.     

南亚季风环流与臭氧时空分布变化关系的特征分析

利用2005年1月至2017年12月搭载在美国环境监测Aura卫星上的臭氧监测仪（Ozone Monitoring Instrument, OMI）数据和NCEP气象资料,在夏季风环流指数定义方法的基础上,重新定义了南亚区域冬季风环流指数,并分别计算了南亚夏季风和冬季风环流指数. 结合冬夏两季环流的强弱变化采用相关分析、合成分析和奇异值分解（Singular Value Decomposition, SVD）等方法,探讨了环流异常形势下臭氧的时空变化特征. 结果表明:①南亚夏季纬向环流与经向环流的强度变化存在一致性,冬季经向环流与纬向环流的强度变化差异较大. ②南亚臭氧柱总量的季节变化明显,且近13年来臭氧柱总量整体呈上升趋势. ③夏季（冬季）风环流指数与对流层中低（中高）层和平流层中低层臭氧的相关性显著,但夏季平流层和对流层的相关趋势相反. ④夏季风环流增强对应青藏高原?伊朗高原上空及南侧区域的上升运动增强,对臭氧的输送作用是造成对流层臭氧分布呈现差异的原因. ⑤冬季风环流强弱期的垂直上升和下沉运动中心的移动,以及南北向、东西向气流交汇区的差异是造成臭氧分布不同的原因.     

Anti-correlation of summer/winter monsoons?

On the basis of the anti-correlation of their palaeoclimatic proxy for the strength of the East Asian winter monsoon from Lake Huguang Maar, China, with stalagmite records of the strength of the summer monsoon, Yancheva et al. claim that the strengths of the summer and winter monsoons are anti-correlated on a decadal timescale. They argue that the summer rainfall deficit during ad 700-900 that they infer from their evidence of a stronger winter monsoon, in conjunction with a Tanros battle, led to the collapse of the Tang dynasty (ad 618-907). Using historical climate records, we show here that most cold winters during ad 700-900 were associated with relatively wet summers, indicating that the strengths of the winter and summer monsoons were not negatively correlated during this period.