Paleoglacial and paleoclimate reconstructions during the global Last Glacial Maximum in the Longriba area, eastern Tibetan Plateau

Owing to the remoteness of the Longriba area and the lack of dating records,it is extremely challenging to reconstruct the chronology and extent of the paleoglaciers in this area.In this paper,we combined limited observational data with automated modelling for paleoglacial reconstructions.We first identified a broadly distributed paleoglacier from satellite imagery and field investigation based on the sediment-landform assemblage principle and dated it to 23.1±1.4~19.5±1.2 ka by ^(10)Be exposure dating,corresponding to the global Last Glacial Maximum(gLGM).Then,we reconstructed the extent and ice surface of 171 paleoglaciers formed during the similar period based on geomorphological evidence and‘ice surface profile’modelling.The results showed that the paleoglacial coverage was 426.5 km2,with an ice volume of 38.1 km^(3),in the Longriba area.The reconstructed equilibrium line altitudes(ELAs)based on modelled ice surfaces yielded an average of 4245±66 m above sea level(asl),~725±73 m lower than the present ELA(4970±29 m asl).The temperature was~5.51-6.68℃lower,and the precipitation was~30-34%less in Longriba,during the gLGM compared to the present day.This glacial advance was mainly driven by colder climate that was synchronous with Northern Hemisphere cooling events.

Long-range precipitation forecasts using paleoclimate reconstructions in the western United States

Long-range precipitation forecasts are useful when managing water supplies.Oceanicatmospheric oscillations have been shown to influence precipitation.Due to a longer cycle of some of the oscillations,a short instrumental record is a limitation in using them for long-range precipitation forecasts.The influence of oscillations over precipitation is observable within paleoclimate reconstructions;however,there have been no attempts to utilize these reconstructions in precipitation forecasting.A data-driven model,KStar,is used for obtaining long-range precipitation forecasts by extending the period of record through the use of reconstructions of oscillations.KStar is a nearest neighbor algorithm with an entropy-based distance function.Oceanic-atmospheric oscillation reconstructions include the El Nino-Southern Oscillation(ENSO),the Pacific Decadal Oscillation(PDO),the North Atlantic Oscillation(NAO),and the Atlantic Multi-decadal Oscillation(AMO).Precipitation is forecasted for 20 climate divisions in the western United States.A 10-year moving average is applied to aid in the identification of oscillation phases.A lead time approach is used to simulate a one-year forecast,with a 10-fold cross-validation technique to test the models.Reconstructions are used from 1658-1899,while the observed record is used from 1900-2007.The model is evaluated using mean absolute error(MAE),root mean squared error(RMSE),RMSE-observations standard deviation ratio(RSR),Pearson's correlation coefficient(R),NashSutcliffe coefficient of efficiency(NSE),and linear error in probability space(LEPS) skill score(SK).The role of individual and coupled oscillations is evaluated by dropping oscillations in the model.The results indicate 'good' precipitation estimates using the KStar model.This modeling technique is expected to be useful for long-term water resources planning and management.

Latest Neogene Paleoclimate Variation in Yunnan,Southwest China,Revealed by Fossil Leaf Physiognomy

Yunnan Province,located in the southeastern margin of the Tibetan Plateau,can provide important information on how climate change was influenced by global cooling.However,its variation patterns in temperature and precipitation during the latest Neogene are not well-understood.Based on the 357 specimens assigned to 31 morphotypes of plant fossils from the upper Pliocene Ciying Formation in Yiliang County,Yunnan Province,Southwest China,paleoclimate was estimated by Leaf Margin Analysis and Climate Leaf Analysis Multivariate Program.Compared to the present climate,the mean annual temperature and coldest month temperature have not changed significantly since the late Pliocene,whereas the warmest month temperature has decreased significantly.All precipitation-related parameters have decreased,particularly winter precipitation.Combined with the climatic data of the same period in other areas of Yunnan,the western and eastern Yunnan has shown a similar pattern in temperature variation since the late Pliocene except for central Yunnan;whereas the variation in precipitation does not follow a common law except for a consistent decrease in winter precipitation.Our study reinforced the fact that under the background of global cooling and intensified monsoon systems,different areas of Yunnan exhibit different climatic responses to these changes because of their topographic heterogeneities.

Influences of air CO2 on hydrochemistry of drip water and implications for paleoclimate study in a stream-developed cave, SW China

Cave air CO_2 is a vital part of the cave environment. Most studies about cave air CO_2 variations are performed in caves with no streams; there are few studies to date regarding the relationship of cave air CO_2 variations and drip water hydrochemistry in underground stream–developed caves. To study the relationship of underground stream, drip water, and cave air CO_2, monthly and daily monitoring of air CO_2 and of underground stream and drip water was performed in Xueyu Cave from 2012 to 2013.The results revealed that there was marked seasonal variation of air CO_2 and stream hydrochemistry in the cave. Daily variations of cave air CO_2, and of stream and drip water hydrochemistry, were notable during continuous monitoring.A dilution effect was observed by analyzing hydrochemical variations in underground stream and drip water after rainfall. High cave air CO_2 along with low p H and low δ^(13)C DIC in stream and drip water indicated that air CO_2 was one of the dominant factors controlling stream and drip water hydrochemistry on a daily scale. On a seasonal scale, stream flows may promote increased cave air CO_2 in summer; in turn, the higher cave air CO_2 could inhibit degassing of drip water and make calcite δ^(13)C more negative. Variation of calcite δ^(13)C(precipitated from drip water) was in reverse of monthly temperature, soil CO_2, and cave air CO_2. Therefore,calcite δ^(13)C in Xueyu Cave could be used to determine monthly changes outside the cave. However, considering the different precipitation rate of sediment in different seasons,it was difficult to use stalagmites to reconstruct environmental change on a seasonal scale.

Primary Study on Quantitative Reconstruction of Middle-Late Eocene Climate in Jianghan Basin

This paper reports our primary effort in the quantitative reconstruction ofpaleoclimate based on the thrine in phytoecology of the affinity parent plants in the stratigraphicpollen records. The Eocene pollen data come from our former study on the Mingjia borehole 1 in theJianghan basin. The fluctuating trend in the parameter curve of climate shows that the climate inthe Middle Eocene in the Jianghan basin was more or less comparable with that of the present22°―26°N, characteristic of a humid, semi-humid central-southern subtropical climate. The annualtemperature at that time dropped by 1 ℃― 4 ℃ in the Late Eocene, approximately equal to that ofthe present 23°―28°N of northern-central subtropical climate. However, the climate composite atthat time, characterized by higher temperature, small annual range and big fluctuation inprecipitation, was quite different from the present one. The average temperature in January in theMiddle Eocene, higher than that of today, ranged between 5 ℃ and 9 ℃, indicating that no effect ofwinter monsoon occurred in the Middle Eocene, though such an effect may have occurred occasionallyin the Late Eocene. Major temperature decline is recognized at the depth of 2 100 m in the borehole,as was indicated by the decline in average January temperature, the increase in annual range, andthe increase in the deciduous broad-leaved types of trees in the spore-pollen assemblage. The sharpfluctuation in the annual precipitation, usually raging from 300 to 1 700 mm, was favorable for themigration and accumulation of salty deposit. When the precipitation was lower than 1 000 mm,ephemera shrub increased at the same depth as that of the salty deposit. It is, therefore, deducedthat the formation of the salty deposit was attributed mainly to the dry and hot environment in thehigh mountains and deep basins. The small annual precipitation and the intense fluctuation arefavorable for the sustainable accumulation of the salts, which is different from the present saltyaccumulation in the Northwest China.

Characteristics of CO_2 in unsaturated zone(～90 m) of loess tableland, Northwest China

In order to observe CO_2 characteristics in the unsaturated zone of loess tableland and further understand the carbon cycle,a series of tubes for gas monitoring and sampling were installed in an approximately 90-m deep Qiushe loess section of Lingtai County,Northwestern China.The results show that the concentration of CO_2 was higher in loess than in the atmosphere,reaching a maximum of 6970 lmol·mol^(-1).CO_2 concentrations in loess were higher in summer than in winter.The CO_2 in loess was related to organic carbon decomposed by microbes,and to the CaCO_3–H_2O–CO_2 system in the interface between the saturated and unsaturated zones.

A quantitative reconstruction of the paleoenviornmental variations of the South Yellow Sea inner shelf based on benthic foraminiferal transfer functions

Transfer functions between the benthic foraminiferal fauna of seventy-one sediment surface-samples retrieved from the South Yellow Sea inner shelf and the environmental factors, including the summer bottom-water salinity(Ss), the summer bottom-water temperature(Ts) and the winter bottom-water temperature(Tw) have been developed utilizing weighted averaging partial least square regression(WA-PLS). Subsequently, the transfer functions have been applied to a late Holocene piston core SY01 from the South Yellow Sea inner shelf, established the variation curves of the Ss, Ts, and Tw during the last 3.9 cal. ka. The Ss and Ts showed a nearly synchronous trend to the published stalagmite δ18O curve from the Jiuxian Cave, meaning they could be used as reliable indicators for the summer monsoon. Similarly, the Tw could be used as an indicator for the winter monsoon for its synchronous change to the insensitive grain size variation of the core ZY-2 retrieved from the Central Yellow Sea mud area. These results suggest that transfer functions based on benthic foraminiferal fauna can be a potentially useful tool in palaeoceanographic and palaeoenvironmental research along the Chinese seaboard.

Development background of Mesozoic high-quality source rocks: Evidence from microfossils in North Carnarvon Basin, Australia

Based on numerous microfossils in Mesozoic of North Carnarvon Basin in Australia,the Mesozoic paleoclimate and paleoenvironment were analyzed,the paleogeographic background and development model of Mesozoic high-quality source rocks were investigated and discussed.Variation of microfossil species and their relative contents in Mesozoic different intervals indicates changes of paleoclimate and paleoenvironment.The paleoclimate shows a cycle variation of aridehumidearidehumid,the regression occurred in the Early TriassiceLate Triassic and the transgression occurred in the Late TriassiceLate Cretaceous.Four sedimentary facieses including delta facies,littoral facies,restricted sea facies and open sea facies were developed in the Mesozoic.The open sea was mainly developed in the Early Triassic,the delta was distributed in the MiddleeLate Triassic,the restricted sea was especially well developed in the Jurassic,and the restricted sea and open sea were mainly distributed in the Cretaceous.Characteristics of microfossil assemblage in these four sedimentary facies are dramatically different.From the delta facies,littoral facies,restricted sea facies to open sea facies,content of pollen gradually decreases,but content of the dinoflagellate+acritarch gradually increases.The delta facies and littoral facies are dominated by the pollen.In the restricted sea facies,content of the pollen is equivalent to that of the dinoflagellate+acritarch.The open sea facies is dominated by the dinoflagellate and acritarch.Supply of sediment and formation of organic matter are influenced by the paleoclimate and paleoenvironment,and type of organic matter is controlled by the microfossil assemblage.Based on the palaeogeographic background,paleoclimatic condition and microfossil assemblage,two developmental models of the Mesozoic source rocks such as the development model of terrestrial organic matter under the background of large delta and the development model of mixed organic matter under the background of the restricted sea,were proposed.

Stable isotopes in atmospheric water vapour:Patterns,mechanisms and perspectives

Stable isotopes in atmospheric water vapour are important tracers for investigating water vapour transport, mixing and phase transition. In recent years, with the rapid development of analytical techniques, research on water vapour stable isotopes has been widely conducted worldwide. In this review, we summarize basic theory and examine various methodologies employed to study stable isotopes in atmospheric water vapour, ranging from traditional collection methods to more recent advancements in laser absorption spectroscopy, satellite remote sensing, and isotope general circulation models(iGCMs). We pointed out the critical role played by isotopes in tracing moisture sources, understanding precipitation patterns, and reconstructing past climates. We identify gaps in knowledge, particularly in the representation of isotopic processes in climate models. Furthermore, we highlighted future research should focus on enhancing isotopic measurement technologies, integrating isotopic data with climatic indicators to improve model accuracy, and expanding isotopic studies to underserved water cycle dynamics. This review aims to provide suggestions for future investigations to deepen our understanding of atmospheric water vapour stable isotopes and their significance in climatology and hydrology.