Spatial distribution of charcoal in topsoil and its potential determinants on the Tibetan Plateau

As an important proxy for investigating past fire activities,charcoal is often used to explore the characteristics of fire distribution and its relationships with vegetation,climate,and human activities.Research into the spatial distribution and environmental determinants for charcoal,however,is still limited.In this study,we identified and counted charcoal from topsoil samples covering the Tibetan Plateau using the pollen methodology,and investigated its relationships with vegetation net primary production(NPP),elevation,climate(precipitation,mean temperature of the coldest month and warmest month)and human population by boosted regression trees(BRT).Results reveal that the concentration of microscopic charcoal,macroscopic charcoal,and total charcoal all increase from south-west to north-east,which is consistent with the trend that the population density on the Tibetan Plateau is high in the east and low in the west,suggesting that an increase in human activity is likely to promote the occurrence of fire.The BRT modeling reveals that NPP,elevation,and mean temperature of the coldest month are important factors for total charcoal concentration on the Tibetan Plateau,and the frequency and intensity of fires further increase with increasing vegetation biomass,decreasing elevation,and decreasing mean temperature of the coldest month.The spatial variation characteristics of charcoal from topsoil on the Tibetan Plateau not only reflect well the spatial fire situation in the region,but also have a good indicative significance for vegetation,climate,and human activities.

Wetland science,ecosystem services and protection actions in China

Wetlands are widely recognized as among Earth’s most vital ecosystems.They occupy a mere 5%−8%of our global landmass,but provide unparalleled ecosystem services per unit area compared to any other habitats.Wetlands provide not only sustenance and shelter for livelihoods but also essential ecosystem functions,including biodiversity preservation,climate regulation,hydrological flow regulation,and water purification.For example,wetlands serve as biogeochemical hotspots,actively participating in greenhouse gas exchanges between the Earth’s surface and the atmosphere[1],and peatlands-peataccumulating wetlands-contain the highest soil carbon density and the largest biosphere carbon pool among all ecosystems[2].Often referred to as the“kidney of the world”,wetlands excel at removing pollutants and purifying water。

Dispersal of crop-livestock and geographical-temporal variation of subsistence along the Steppe and Silk Roads across Eurasia in prehistory

The innovations of agricultural production and their extensive dispersal promoted the transformation of human livelihoods and profoundly influenced the evolution of human-land relationships in late prehistoric Eurasia.The Steppe and Silk Roads(SSRs)played important roles in the transcontinental exchange and dispersal of cereal crops and livestock related to agricultural innovation across Eurasia before the Han Dynasty(202 BC to AD 220),while the geographical-temporal variations in prehistoric subsistence in relation to the spread and exchange of cereal crops and livestock originating from different areas of Eurasia still remain unclear.In this paper,we explore these issues based on the review and analysis of published archaeobotanical,zooarchaeological,and carbon-stable isotope data from human bones from Neolithic-Early Iron Age sites in areas along the SSRs,with a comparison to updated results based on radiocarbon dating and ancient DNA analyses.Our results suggest that humans engaged in hunting game,while foxtail/broomcorn millet cultivation gradually became the primary subsistence strategy in Eastern SSRs from 10,500 to 6000 a BP.In contemporaneous Western SSRs,humans mainly cultivated wheat/barley and raised sheep/goats,cattle,and pigs.Trans-Eurasian exchange,which is reflected by the mixed utilization of wheat/barley and millet,emerged in the south-central Steppe during 6000–4000 a BP,while millet cultivation and pig husbandry became the dominant livelihoods in most areas of Eastern SSRs.During 4000–2200 a BP,Silk Roads became the major passageway for trans-Eurasian exchange,the interactive development of oasis agriculture and pastoralism facilitated intensive human settlement in the Central Silk Roads,and subsistence strategies substantially changed with significant geographical differences in Eastern SSRs,while subsistence in some areas of Western SSRs was evidently affected by the introduction and adoption of millet crops after 3000 a BP.The geographical-temporal variations in subsistence in the SSRs from the Neolithic to Early Iron Age were primarily affected by the prehistoric dispersal of farming groups across Eurasia,which was accompanied by the spread of cereal crops/livestock,while the impacts of climate change still need to be further evaluated.

Increased water vapor supply in winter and spring leading to the arid Central Asian wetting in last 6000 years

Paleoclimate reconstructions show that the arid Central Asia(ACA)is characterized by a wetting trend from the midHolocene(MH)to the Preindustrial period(PI),which has been acknowledged to be a result of increased mean precipitation.However,a systemic understanding of its governing dynamics remains elusive.Based on model outputs from 13 climate models from the Paleoclimate Model Intercomparison Project phase 4(PMIP4)and proxy records from ACA,here we show that increase in mean precipitation in ACA can be attributed to changes in water vapor source and its transport intensity in winter(December,January,and February)and spring(March,April,and May).In particular,the increase in water vapor supply in winter is associated with the southerly wind anomaly over the northwestern Indian Ocean and Central Asia,caused by an overall weakening of the Asian winter monsoon.This is conducive to water vapor transport from the upwind regions(e.g.,Mediterranean)to ACA.Meanwhile,water vapor supply from the eastern Iceland is also enhanced due to a negative North Atlantic Oscillation-like(NAO-like)atmospheric circulation pattern caused by sea ice expansion in the North Atlantic.In spring,evaporation over land and inland lakes is enhanced by increased insolation in the Northern Hemisphere,which increases atmospheric humidity that fuels midlatitude westerlies to enhance ACA precipitation.In addition,weakened atmospheric subsidence over ACA in winter and spring also contributes to the increased precipitation.Overall,our results indicate that paleoclimate modeling is of great importance for disentangling governing dynamics accounting for reconstructed climate phenomena that might be a synergic consequence of several processes operating in different seasons.

Influence of plant coverage and environmental variables on pollen productivities:evidence from northern China

Pollen productivity is a critical parameter in the interpretation of pollen-vegetation relationships,and in the quantitative reconstructions of past vegetation from fossil pollen records.One-year monitoring records were collected for 143 pollen traps in various parts of northern China,together with modern vegetation data.Absolute Pollen Productivity Estimates(APPE)were calculated for 11 taxa using the ratio of pollen influx to plant coverage at each applicable sampling site,in which the plants of the target taxon were present.Relative Pollen Productivity Estimates(RPPE)were calculated for the 11 taxa(taking Poaceae as the reference taxon)at those sites in which each taxon occurred together with Poaceae.Artemisia and Chenopodiaceae were found to have the highest RPPEs and the largest RPPEs ranges,while Pinus and Quercus also had higher RPPEs than Poaceae;Abies,Betula,Larix,Picea and Cyperaceae had relatively low RPPEs.Variations in RPPE between different areas may be explained by variations in climatic conditions,plant coverage and land use practices which might influence plant growing situation.Marked effect that variations in pollen productivity can have on vegetation reconstructions was demonstrated by applying these distinct RPPEs to reconstructions of Holocene vegetation in the Lake Daihai area(northern China),such as a large range of RPPE produces a large range of plant coverage.Variations in RPPEs within a single taxon,related to vegetation coverage and climatic conditions,therefore need to be considered in future vegetation reconstructions.

Holocene temperature variation recorded by branched glycerol dialkyl glycerol tetraethers in a loess-paleosol sequence from the north-eastern Tibetan Plateau

Reconstructing Holocene temperature evolution is important for understanding present temperature variations and for predicting future climate change,in the context of global warming.The evolution of Holocene global temperature remains disputed,due to differences between proxy reconstructions and model simulations,a discrepancy known as the῾Holocene temperature conundrum᾽.More reliable and quantitative terrestrial temperature records are needed to resolve the spatial heterogeneity of existing records.In this study,based on the analysis of branched glycerol dialkyl glycerol tetraethers(brGDGTs)from a loess-paleosol sequence from the Ganjia Basin in the north-eastern Tibetan Plateau(NETP),we quantitatively reconstructed the mean annual air temperature(MAAT)over the past 12 ka.The MAAT reconstruction shows that the temperature remained low during the early Holocene(12−8 ka),followed by a rapid warming at around 8 ka.From 8 to 4 ka,the MAAT record reached its highest level,followed by a cooling trend from the late Holocene(4−0 ka).The variability of the reconstructed MAAT is consistent with trends of annual temperature records from the Tibetan Plateau(TP)during the Holocene.We attribute the relatively low temperatures during the early Holocene to the existence of ice sheets at high-latitude regions in the Northern Hemisphere and the weaker annual mean insolation at 35°N.During the mid to late Holocene,the long-term cooling trend in the annual temperature record was primarily driven by declining summer insolation.This study provides key geological evidence for clarifying Holocene temperature change in the TP.

Vegetation stability during the last two centuries on the western Tibetan Plateau:a palynological evidence

Investigating the dynamics of vegetation is an essential basis to know how to protect ecological environments and to help predict any changes in trend.Because of its fragile alpine ecosystem,the Tibetan Plateau is a particularly suitable area for studying vegetation changes and their driving factors.In this study,we present a high-resolution pollen record covering the last two centuries extracted from Gongzhu Co on the western Tibetan Plateau.Alpine steppe is the predominant vegetation type in the surrounding area throughout the past 250 years with stable vegetation composition and abundance,as revealed by pollen spectra dominated by Artemisia,Ranunculaceae,Cyperaceae,and Poaceae.Detrended canonical correspondence analysis(DCCA)of the pollen data reveals low turnover in compositional species(0.41 SD),suggesting that the vegetation in the Gongzhu catchment had no significant temporal change,despite climate change and population increases in recent decades.We additionally ran DCCA on ten other pollen records from the Tibetan Plateau with high temporal resolution(1-20 years)covering recent centuries,and the results also show that compositional species turnover(0.15-0.81 SD)is relatively low,suggesting that the vegetation stability may have prevailed across the Tibetan Plateau during recent centuries.More high-resolution pollen records and high taxonomic-resolution palaeo-vegetation records(such as sedaDNA),however,are needed to confirm the vegetation stability on the Tibetan Plateau.

The Holocene environmental changes revealed from the sediments of the Yarkov sub-basin of Lake Chany,south-western Siberia

Lake Chany is the largest endorheic lake in Siberia whose catchment is entirely on the territory of Russia.Its geographical location on the climate-sensitive boundary of wet and dry landscapes provides an opportunity to gain more knowledge about environmental changes in the West Siberian interior during the Holocene and about the evolution of the lake itself.Sediment cores obtained from the Yarkov subbasin of the lake in 2008 have been comprehensively studied by a number of approaches including sedimentology and AMS dating,pollen,diatom and chironomid analyses(with statistical interpretation of the results),mineralogy of authigenic minerals and geochemistry of plant lipids(biomarker analysis.).Synthesis of new results presented here and published data provides a good justification for our hypothesis that Lake Chany is very young,no older than 3.6 ka BP.Before that,between 9 and 3.6 ka BP,the Chany basin was a swampy landscape with a very low sedimentation rate;it could not be identified as a water body.In the early lake phase,between 3.6 and 1.5 ka BP,the lake was shallow,1.2–3.5 m in depth,and it rose to its modern size,up to 6.5 m in depth,during the last millennium.Our data reveal important changes in the understanding of the history of this large endorheic lake,as before it was envisioned as a large lake with significant changes in water level since ca.14 ka BP.In addition to hydrology,our proxies provide updates and details of the regional vegetation and climate change since ca.4 ka BP in the WestSiberian forest-steppe and steppe.As evolution of the Chany basin is dependent on hydroclimatic changes in a large region of southern West Siberia,we compare lake-level change and climate-change proxies from the other recently and most comprehensively studied lakes of the region.

中国地理科学学科体系

International and domestic circumstances have led to new opportunities and higher requirements for the development of geographic science in China.In this paper,we propose a modified disciplinary structure for geographic science in China in the new era.Geographic science in China can be categorized into four secondary disciplines,i.e.,integrated geography,physical geography,human geography,and information geography,according to the current situation and expected trends.The tertiary disciplines under each secondary discipline are nearly fully developed,and a few quaternary disciplines under the tertiary disciplines are widely accepted and used in China.We hope this new disciplinary structure can play a breakthrough role in improving the branches of geographic science,promoting the development of emerging disciplines under the framework of geographic science,and supporting national and international development strategies in the new era.

Spatial homogenization of soil-surface pollen assemblages improves the reliability of pollen-climate calibration-set

To make a reliable reconstruction of past climate from soil-surface modern pollen,it is necessary to reduce the sources of error.In this paper,pollen percentages of the sub-continental scale modern pollen-climate dataset from China and Mongolia(with 68%soil-surface samples)are homogenized at various spatial scales.A tailored calibration-set is then applied to lake sediment-surface pollen assemblages from north-central China to evaluate their predictive power.Results indicate that spatial homogenization of modern pollen percentages can increase the proportion of inertia explained by climatic variables in CCA and improve the model performance of leave-one-out cross-validation using WA-PLS.Soil-surface pollen assemblages can thus be employed into a calibration-set for reliable climate estimation and they perform better when the calibration-set has been locally homogenized.Small-scale(e.g.,radii 2,5,or 10 km)homogenization reduces the local noise in soil-surface pollen assemblages and improves the cross-validated performance,while broader scale homogenization(more than 20 km radius)blurs the pollen-climate relationship.Lake sediment-surface pollen assemblages from close to the shore could contain pollen grains transported by rivers or from the shore vegetation and thus fail to represent regional climate well like the assemblages from the central part and deep-water area of lake.

自然地理学学科体系与发展战略要点

Physical geography,one of the branches of geography,is the basic discipline of geographic science.And it is the scientific foundation of ecology,environmental science and other related disciplines.Physical geography focuses on spatial characteristics,evolution and regional differentiation of the earth’s surface.In the new period of rapid development of social economy,and science and technology,physical geography is more closely and widely connected with human geography and,information geography.This paper analyzed the forming process of the physical geography,expressed sub-discipline structure of integrated physical geography,sectoral physical geography,human living-environment geography,and proposed the development strategy of physical geography and its sub-branch disciplines,key priority of development goals and directions in China.

Erratum to:Holocene temperature variation recorded by branched glycerol dialkyl glycerol tetraethers in a loess-paleosol sequence from the north-eastern Tibetan Plateau

Erratum to:Front.Earth Sci.DOI 10.1007/s11707-023-1094-6 The original version of this article unfortunately contained a mistake.The presentation of was incorrect.The corrected figure is given below.