North Atlantic Abrupt Climate Signals during the Last Glacial Period in Central Asia：Evidences from Aeolian Loess Sediments

Objective Climate fluctuations over suborbital or millennial timescale display significant instability during the last glacial period,which are often superimposed upon the orbital periodicity.They triggered some abrupt climate events,

Spatial / Temporal Features of Antarctic Climate Change

Bused on January 1962-October 1993 mean value series of monthly mean temperature anomalies of 16 Antarctic stations on 10 standard isobanc surfaces from the surface to the 30 hPa,long term trends and periodic features of climate changes from the troposphere to the lower stratosphere over the Antarctic region are investigated by maximum entropy power spectrum analysis,and the relation between climate change of the stratosphere (troposphere) and tolal ozone (southern 500 hPa circulation) is discussed.

High-frequency climatic fluctuations over the past 30 ka in northwestern margin of the East Asian monsoon region, China

Whether millennial-to centennial-scale climate variations throughout the Holocene convey universal climate change is still widely debated.In this study,we aimed to obtain a set of high-resolution multi-proxy data(1343 particle size samples,893 total organic carbon samples,and 711 pollen samples)from an alluvial-lacustrine-aeolian sequence based on an improved age-depth model in the northwestern margin of the East Asian monsoon region to explore the dynamics of climate changes over the past 30 ka.Results revealed that the sequence not only documented the major climate events that corresponded well with those reported from the North Atlantic regions but also revealed many marked and high-frequency oscillations at the millennial-and centennial-scale.Specifically,the late stage of the last glacial lasting from 30.1 to 18.1 cal.ka BP was a dry and cold period.The deglacial(18.1-11.5 cal.ka BP)was a wetting(probably also warming)period,and three cold and dry excursions were found in the wetting trend,i.e.,the Oldest Dryas(18.1-15.8 cal.ka BP),the Older Dryas(14.6-13.7 cal.ka BP),and the Younger Dryas(12.5-11.5 cal.ka BP).The Holocene can be divided into three portions:the warmest and wettest early portion from 11.5 to 6.7 cal.ka BP,the dramatically cold and dry middle portion from 6.7 to 3.0 cal.ka BP,and the coldest and driest late portion since 3.0 cal.ka BP.Wavelet analysis results on the total pollen concentration revealed five substantially periodicities:c.5500,2200,900,380,and 210 a.With the exception of the c.5500 a quasi-cycle that was causally associated with the Atlantic meridional overturning circulation,the other four quasi-cycles(i.e.,c.2200,900,380,and 210 a)were found to be indirectly causally associated with solar activities.This study provides considerable insight into the dynamic mechanism of the Asian climate on a long-time scale and future climatic change.

HISTORICAL EVIDENCE ON CLIMATIC INSTABILITY ABOVE NORMAL IN COOL PERIODS IN CHINA

Twenty-six sequences of grades of dryness/wetness and a combined sequence of indexes of winter temperature since A.D. 1471 in China were adopted as our data. The fluctuations of variability of precipitation and mean temperature are statistically significant from analyses. It has been found that in middle latitudes of eastern China the distribution of the relation between mean temperature and interannual variability of precipitation in historical time forms a rather complex regional pattern, and the correlation coefficients are not unique in signs. But the negative correlations are dominant either in extent or in magnitude. The authors provide evidence that Little Ice Age was a time of more frequent extremes and support the idea that the climatic instability is above normal in cool periods.

Variations in monsoon precipitation over southwest China during the last 1500 years and possible driving forces

Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period(MWP),the Little Ice Age(LIA),and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios.In this study,based on ^(210)Pb and ^(137)Cs dating of surface sediments and AMS ^(14)C dating of terrestrial plant residues,we establish a robust age model that covers the last~1500 years(AD 439–2012)at Lake Yihai in southwest China.We use analyses of multiple geochemical proxy indices,including loss on ignition at 550℃,total organic carbon,total nitrogen,C/N ratios,and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last~1500 years.The results show that,over southwest China,warm and dry climate conditions prevailed during the MWP(AD 1000–1400)and the past 200 years,whereas conditions during the LIA(AD 1400–1800)were cold and wet.This is consistent with evidence from other geological records over southwest China,such as stalagmite and lake sediment data.Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon(e.g.,South China,the South China Sea,Southeast Asia,Northeast India).We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone,and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature,are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years.