vegetation history climate change and human activities over the last 6200 years on the liupan mountains in the southwestern loess plateau in central china abstract fossil pollen data from tianchi lake on the liupan mountains in the loess plateau in china were used to investigate the interplay of climate change vegetation history and human activities the chronology of an 11 m long sediment core was controlled by 19 accelerator mass spectrometry radiocarbon dates on terrestrial plant macrofossils the pollen record shows a long term change from a closed canopy forest to open landscape over the last 6200 years from mixed deciduous coniferous forest dominated by betula quercus picea and pinus at 6200 2900 cal yr bp to transitional steppe forest co dominated by trees betula picea and pinus and herbs mostly artemisia at 2900 1100 cal yr bp and to open landscape dominated by artemisia and poaceae after 1100 cal yr bp this general pattern of vegetation change indicates a drying climate trend consistent with other independent climate records mostly from the monsoon region that show a weakening summer monsoon since the mid holocene the gradual increase in both poaceae pollen and microscopic charcoal since about 2000 cal yr bp and a sharp increase in poaceae but a decrease in charcoal at 1000 cal yr bp indicate two phases of human impacts on vegetation the results from pollen and charcoal analysis together with archaeological and historical evidence suggest that human activities over the last 2000 years have significantly accelerated deforestation that was initiated by a drying climate since the mid holocene

aeolian sediments evolution controlled by fluvial processes climate change and human activities since lgm in the qaidam basin qinghai tibetan plateau abstract aeolian sediments are widely distributed in the eastern qaidam basin qb the main habitats for human in the hyper arid basin during the holocene especially since 3 ka the evolution of aeolian sediments is an important factor for the environmental change and influence human activities and migration however many questions e g when the aeolian sediments start to accumulate what controls their initiation and how their evolution responds to climate change and human activities still need further studies in this study we present a detailed optically stimulated luminescence osl chronology for both aeolian and underlying fluvial sediments from the tiekui desert in the eastern qb to discuss aeolian and fluvial processes climatic changes desert evolution and human activities dating results show that 1 underlying fluvial sediments were formed during 23 9 12 1 ka and the erosion caused by the fluvial process may provide an explanation for the absence of aeolian sediments during and before this period 2 aeolian sediments accumulated from ca 9 8 ka to modern times with loess development from 9 8 ka to 1 6 ka and 1 4 0 7 ka and dune sand accumulation at 1 6 1 4 ka and 0 7 0 ka through the comparison with the local and global palaeoclimatic records we suggest that desert evolution in this region was sensitive to climatic changes induced by the asian summer monsoon detailed local historical records of the past 2000 years suggest that desert evolution was also influenced by human activities

holocene climate changes in the monsoon arid transition reflected by carbon concentration in daihai lake of inner mongolia two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for total inorganic and organic carbon tic and toc concentrations the tic concentration is inferred to reflect temperatures over the lake region and an increase in the tic concentration implies an increase in the temperature toc concentration is considered to reflect the precipitation in the lake basin and higher toc concentrations denote more precipitations thus ams 14c time series of the tic and toc records of daihai lake sediments uncovers a detailed history of changes in temperature and precipitation in north central china during the last c 12 000 yr the holocene an epoch of postglacial warmth started c 11 500 cal yr bp and can be subdivided into three stages the early c 11 500 8100 cal yr bp middle c 8100 3300 cal yr bp and the late holocene c 3300 0 cal yr bp the climate was warm and dry during the early holocene warm and wet during the middle holoce

estimating scattering attenuation from vugs or karsts cavities in carbonate rock such as vugs or karsts cause scattering attenuation in passing waves the degree of such attenuation is often difficult to quantify because the exact scale and structure of the cavities is unknown taking the exact vug structure from x ray computerized tomography scans of two carbonate cores we use 3d finite difference modeling to determine the p wave scattering attenuation in these cores at ultrasonic frequencies the predicted scattering attenuation is quite high with q of 15 and 8 near the source frequency of 250 khz in spite of the sharp contrast in medium properties between cavity and rock and the violation of the small perturbation assumption the computed scattering attenuation is roughly comparable to that predicted by various random medium scattering theories this suggests that if the volume fraction and typical size of vugs or karsts can be estimated then a rough estimate of frequency dependent scattering attenuation can be made

elemental carbon record of paleofire history on the chinese loess plateau during the last 420 ka and its response to environmental and climate changes an elemental carbon ec record covering the last 420 ka was reconstructed using chemical oxidation method on a loess and paleosol sequence from the lingtai section on the chinese loess plateau the ec record reveals the paleofire history and its relationship with climate and vegetation changes on the chinese loess plateau our results show that the ec abundance is generally higher in the paleosols than in the loess layers showing a glacial interglacial pattern which is coincident with biomass changes this variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions the ec abundance increases sharply at similar to 130 kab p indicating a dramatic change in the vegetation and climate variation patterns the occurrence of a peak value with the highest average ec abundance in the holocene may reflect the occurrence of a major climate event at similar to 6 kab p and may also be partly due to more frequent anthropogenic fire usages c 2007 elsevier b v all rights reserved

late pleistocene fire in the ili basin central asia and its potential links to paleoclimate change and human activities abstract evidence of late pleistocene fire activity in central asia is important for understanding the underlying processes and controls of fire here two microcharcoal records from two separate loess sections covering the last 70 thousand years kyr in the ili basin are reported the results show that total microcharcoal concentrations are similar in both records and are correlated with insolation indicating consistent basin wide fire trends related to moisture changes driven by insolation in addition two anomalous fire events were identified at 45 35 ka and 6 0 ka we argue that these events are possibly related to ancient human activities rather than to pure natural factors such as sedimentation wind taphonomic change or climate change

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

the effect of varying the source spectrum of a gravity wave parameterization in a middle atmosphere general circulation model climate simulations of the middle atmosphere circulation with general circulation models are now starting to include parameterizations of the momentum flux deposition due to unresolved gravity wave spectra a current uncertainty in the application of such parameterizations is the specification of the imposed gravity wave spectrum the aim of this work is to quantify the effect of varying within a realistic range the source spectrum of a gravity wave parameterization in a general circulation model results from two simulations with the gravity wave spectrum launched at two different heights the surface and the 110 hpa pressure level respectively are compared noteworthy differences found in the simulated middle atmosphere response include the following 1 the average temperature in the southern winter upper stratosphere is about 40 k warmer in the experiment with the surface as the launching height virtually eliminating the typical cold polar bias that affects many general circulation models 2 stronger easterlies in the subtropical summer mesosphere again in the experiment with the surface as the launching height diagnostics of the parameterized gravity waves indicate that in the experiment with the surface as the launching height the net zonal momentum flux transported by the gravity waves is negative just above the troposphere at middle latitudes this negative net momentum flux facilitates the deceleration of the mesospheric winter westerlies the meridional circulation induced by such deceleration is thereafter responsible for the substantial polar winter warming in contrast in summer the negative net momentum flux limits the upper mesospheric deceleration of the easterlies in the experiment with launching height at 110 hpa the gravity wave net momentum flux is instead zero by construction at the launching height

mid holocene climate change and its effect on prehistoric cultural evolution in eastern qinghai province china abstract we studied the mid holocene climate change in eastern qinghai province china and its impact on the evolution of majiayao 3980 2050 bc and qijia 2183 1635 bc cultures near the important neolithic site of changning the investigation focused on analyses of grain size magnetic susceptibility ratios of elemental contents and pollen assemblage from a loess paleosol sequence the results indicate that the climate was wet during 5830 4900 cal yr bp which promoted the development of early mid majiayao culture in eastern qinghai province however 4900 4700 cal yr bp were drought years in the region responsible for the decline and eastward movement of prehistoric culture during the period of transition from early mid to late majiayao culture the climate turned wet again during 4700 3940 cal yr bp which accelerated the spread of qijia culture to the middle reaches of the huangshui river including the changning site

prehistoric human activity and its environmental background in lake donggi cona basin northeastern tibetan plateau lake donggi cona is a key area for the exploration of the prehistoric settlement of the inner tibetan plateau because of its location in the joint of the higher inner tibetan plateau and the upper

detection of the secondary meridional circulation associated with the quasi biennial oscillation 1 the quasi biennial oscillation qbo signal in stratospheric zonal and meridional wind temperature and geopotential height fields is analyzed based on the use of the national centers for environmental prediction ncep reanalysis 1958 2001 the multitaper method singular value decomposition mtm svd a multivariate frequency domain analysis method is used to detect significant and spatially coherent narrowband oscillations the qbo is found as the most intense signal in the stratospheric zonal wind then the mtm svd method is used to determine the patterns induced by the qbo at every stratospheric level and data field the secondary meridional circulation associated with the qbo is identified in the obtained patterns this circulation can be characterized by negative positive temperature anomalies associated with adiabatic rising sinking motions over zones of easterly westerly wind shear and over the subtropics and midlatitudes while meridional convergence and divergence levels are found separated by a level of maximum zonal wind shear these vertical and meridional motions form quasi symmetric circulation cells over both hemispheres though less intense in the southern hemisphere

changes in fire regimes on the chinese loess plateau since the last glacial maximum and implications for linkages to paleoclimate and past human activity abstract a high resolution black carbon bc record from 27 5 kyr bp to present was reconstructed using a chemical oxidation method on loess and paleosol samples from the lijiayuan section of the chinese loess plateau the black carbon mass sedimentation rates bcmsr and carbon isotopic record reveal a paleofire history and its relationship with climate and vegetation changes at the study site the bcmsr record was decomposed into two components background bcmsr and the bcmsr peaks the background bcmsr represents regional fires and shows high fire activities occurred contemporaneous with the younger dryas older dryas heinrich events and greenland stadials as registered in the loess grain size record this suggests a rapid response of regional fires on the loess plateau to abrupt climate changes spectral analysis of background bcmsr showed two meaningful periodicities of 1620 and 1040 years close to the cyclicity of the east asian monsoon as recorded in the stalagmite 18o record in central china this indicates a tight control of millennial scale wet dry changes in the monsoonal climate on regional fires on the loess plateau by contrast the bcmsr peaks are considered to reflect local fire episodes the occurrences of local fires were more frequent during the last glacial period with a maximum frequency of 6 episodes 1000 years during the last glacial maximum lgm 22 3 to 14 6 kyr bp when the climate was drier and more continuous grassy fuels existed on the landscape during the last glacial interglacial transition lgit period 14 6 to 11 0 kyr bp fire frequency was largely reduced due to an increase in precipitation and more woody vegetation if the lgit period is taken as an analog for the projected near future then future global warming alone may not produce large wildfires in northwestern china wildfires remained infrequent during the early to middle holocene biomass burning increased after 4 0 kyr bp when the climate became drier and land use was more intensive bc carbon isotope ratios may well reflect changes in the vegetation being burnt i e grasses versus trees yielding results consistent with the associated pollen data in the region

origin of eolian sand mobilization during the past 2300 years in the mu us desert china abstract eolian sand dunes and sand sheets are extensive in the semiarid regions of northern central china previous studies indicated that these eolian sands mainly formed during historical times however the sand sources and their reworking processes have not been well studied and even the reasons for their occurrence are still controversial field investigation and sedimentary evidence indicate that both the inner mu us desert and its southern marginal region both sources of modern eolian sand are largely associated with reworking of sands of the last glaciation based on geological documentary and archaeological data three phases of land cultivation during the past 2300 years together with historical droughts high wind energy and the easily reworked sand sources largely account for the occurrence of active sand dunes and sand sheets in the mu us desert

postglacial fire vegetation and climate history in the clearwater range northern idaho usa the environmental history of the northern rocky mountains was reconstructed using lake sediments from burnt knob lake idaho and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large scale climate changes during the holocene vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold dry conditions from 14 000 to 12 000 cal yr b p abundant pinus pollen suggests warmer moister conditions than the previous period most sites record the development of a forest with pseudotsuga ca 9500 cal yr b p indicating warm dry climate coincident with the summer insolation maximum as the amplification of the seasonal cycle of insolation waned during the middle holocene pseudotsugawas replaced by pinus and abies suggesting cool moist conditions the fire reconstructions show less synchroneity in general the sites west of the continental divide display a fire frequency maximum around 12 000 8000 cal yr b p which coincides with the interval of high summer insolation and stronger than present subtropical high the sites on the east side of the continental divide have the highest fire frequency ca 6000 3500 cal yr b p and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late holocene this study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher than present fire frequency occurred in the past

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

a new chemical lagrangian model of the stratosphere clams 1 formulation of advection and mixing 1 recent satellite observations and dynamical studies have demonstrated the existence of filamentary structures in chemical tracer fields in the stratosphere it is also evident that such features are often below the spatial resolution of the highest resolution eulerian models that have been used up to the present time these observations have motivated the development of a novel chemical lagranigan model of the stratosphere clams that is based on a lagrangian transport of tracers the description of clams is divided into two parts part 1 this paper concentrates on the lagrangian dynamics i e on the calculation of trajectories and on a completely new mixing algorithm based on a dynamically adaptive grid while part 2 describes the chemical integration and initialization procedure the mixing of different air masses in clams is driven by the large scale horizontal flow deformation and takes into account the mass exchange between the nearest neighbors determined by delaunay triangulation here we formulate an isentropic i e two dimensional version of the model and verify the mixing algorithm using tracer distributions measured during the space shuttle crista 1 experiment where highly resolved stratospheric structures were observed in early november 1994 a comparison of the measured southern hemispheric n2o distribution with clams results allows the intensity of simulated mixing to be optimized the long term robustness of the transport scheme is investigated in a case study of the 1996 1997 northern hemisphere polar vortex this study further provides a dynamical framework for investigations of chemical arctic ozone destruction discussed in part 2

optical dating of tibetan human hand and footprints an implication for the palaeoenvironment of the last glaciation of the tibetan plateau 1 the tibetan plateau is a cold and arid environment with poor archaeological finds it is generally assumed to have been covered by ice sheet during the last ice age nineteen handprints and footprints of homo sapiens on hot spring travertine and the remnant of a fireplace have been found at an elevation of 4200 m on the tibetan plateau based on the optically stimulated luminescence of quartz extracted from samples of the baked and unheated travertine the age of the prints and the fireplace are around 20 000 these finds suggest that there were humans living in this area around the time of the last glacial maximum lgm and that the ice sheet did not cover the entire tibetan plateau at this time

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

spatial and temporal variety of prehistoric human settlement and its influencing factors in the upper yellow river valley qinghai province china abstract we report an investigation of forty two prehistoric sites in the upper yellow river valley located in guide jianzha hualong xunha and minhe qinghai province china including forty four new radiocarbon dates from twenty four sites review published archaeological surveys and radiocarbon dates analyze landform features and discuss the reasons for spatial and temporal variety of regional prehistoric human settlement our results suggest that people occupied the upper yellow river valley during the early holocene but a continuous archaeological record begins only after about 5500 cal yr bp thereafter the intensity of prehistoric human settlement in the area is varied neolithic human settlement spread northwestward to high altitude areas of the upper yellow river valley during early mid majiayao and qijia periods but moved southeastward to lower locations in the area during late majiayao period during the bronze period two coeval archaeological cultures the kayue and xindian occupied the upper yellow river region kayue archaeological sites are numerous and widely distributed in the high areas of the upper yellow river while xindian sites are restricted to the lowest basin of the region variation in site density and location are likely the result of changing paleoclimate and technology

rossby wave phase speeds and mixing barriers in the stratosphere part i observations abstract lagrangian trajectories are used to calculate isentropic mixing properties for unfiltered and filtered southern hemisphere stratospheric winds in wintertime significant mixing is confined to the surf zone between the tropics and the edge of the polar vortex the mixing barrier at the edge of the vortex is located near the core of the polar jet stream where the maximum wind speeds occur which is also approximately where the meridional potential vorticity gradient is largest in summer there is significant mixing throughout the hemisphere and no high latitude mixing barrier exists when the winds are filtered by zonal wavenumber to retain either the planetary scale waves 1 3 or the smaller scale waves 4 12 mixing in the surf zone is generally reduced but not eliminated when the winds are filtered by phase speed however mixing is significantly reduced in restricted latitude zones where the phase speeds of the filtered waves are close to the speed of the local zonal mean zonal wind thes

a model study of the influence of the quasi biennial oscillation on trace gas distributions in the middle and upper stratosphere the dominant tracer transport processes in the equatorial and subtropical latitudes of the middle and upper stratosphere are investigated distributions of water vapor in northern hemisphere winter from the microwave limb sounder onboard the upper atmosphere research satellite are employed together with a three dimensional stratosphere mesosphere model that incorporates a representation of the quasi biennial oscillation qbo the model reproduces the observed tracer distributions in particular a staircase feature that is present in northern winter of 1992 easterly qbo phase but not in 1993 westerly qbo phase this feature is highly asymmetric about the equator the model circulation is diagnosed to show that while the induced qbo circulation in the lower stratosphere of the model is relatively symmetric about the equator in the middle and upper stratosphere it is highly asymmetric and in the correct sense to give rise to the staircase feature model experiments are compared in which trajectories are advected by 1 the full three dimensional circulation and 2 the residual mean circulation only thereby removing the local effects of isentropic mixing by planetary waves on the trajectory distributions these confirm the importance of advection by the qbo circulation at equatorial and subtropical latitudes however sharpening of the tracer gradients at the subtropical edge of the surf zone by the action of planetary waves is shown to be important in the formation of a subtropical cliff between 10 and 20 mbar at 20 30 n the model results also suggest that the prominence of the summer subtropical peak in easterly phase years compared with westerly phase years is not entirely due to increased summer upwelling of the large scale global circulation caused by the stronger planetary wave driving the depression of the winter half of the equatorial peak by the local asymmetric qbo circulation is also shown to be important

quasi biennial and subbiennial variations of stratospheric trace constituents derived from haloe observations interannual variability of trace constituents in the stratosphere is examined using methane water vapor and ozone data from the halogen occultation experiment aboard the upper atmosphere research satellitein 1992 99 application of rotated principal component analysis to the dataset reveals dominant modes of variability consisting of annual semiannual and quasi biennial oscillations qbos together with subbiennial variations evidently due to nonlinear interaction between the annual cycle and qbo the structure of quasi biennial variability is approximately symmetric about the equator while subbiennial variability with certain exceptions is approximately antisymmetric and confined mostly to the subtropics the vertical structure and downward propagation of the ozone qbo at the equator is described by a pair of symmetric eofs having separate amplitude maxima in the lower and upper stratosphere a second pair of eofs explains the seasonal dependence of subtropical ozone anomalies for each tracer the subtropical anomaly is larger in the northern hemisphere a novel phase diagram illustrates the joint seasonal and qbo dependence of tracer anomalies a pair of principal components are used to define the phase of the dynamical qbo when plotted against the phase of the annual cycle the qbo follows a diagonal trajectory with regular phase progression except for an occasional slowing of easterly shear zone descent near 50 hpa tracer principal components of symmetric and antisymmetric eofs plotted along this trajectory display the distinct signatures of quasi biennial and subbiennial variation tracer anomalies reconstructed using an idealized representation of qbo and subbiennial harmonics display the seasonal synchronization and decadal modulation characteristic of qbo annual cycle interaction

holocene east asian monsoon variation inferred from species assemblage and shell chemistry of the ostracodes from hulun lake inner mongolia a sediment core from hulun lake inner mongolia was analyzed for species assemblages and shell chemistry of ostracodes to investigate changes in the hydrology and climate of the east asian summer monsoon margin during the holocene darwinula stevensoni was abundant ilyocypris spp scarce littoral ostracodes absent and mg ca sr ca and 18o were low 11 100 to 8300 yr ago indicating high lake levels and cool fresh waters darwinula stevensoni declined largely ilyocypris spp throve littoral ostracodes were rare and chemical indicators remained in low values 8300 to 6200 yr ago suggesting that the lake continued high stands but water became warm the lake then contracted and water became cool brackish 6200 to 4300 yr ago littoral ostracodes flourished 4300 to 3350 yr ago marking the lowest lake levels of the entire holocene the lake level recovered and water salinity decreased 3350 to 1900 yr ago from 1900 to 500 yr ago the lake maintained the preceding status albeit lowered stands and increased salinities 1100 to 800 yr ago during the recent 500 yr the lake expanded and water salinity decreased the data imply that the east asian summer monsoon did not intensify until 8300 yr ago and weakened dramatically 4300 to 3350 yr ago

late cenozoic fire enhancement response to aridification in mid latitude asia evidence from microcharcoal records fire provides an important indicator of paleoclimatic change however little information relating to late cenozoic fire history has been gathered in mid latitude asia including inner asia and east asia a key region for understanding the development of the arid monsoon climate system as well as the driving forces behind it here we first report the records of microcharcoal concentrations mc covering the holocene 10 0 ica and late pleistocene 0 8 0 ma which we use to analyze the fire activity patterns at an orbital time scale then we compile the late cenozoic mc record to investigate the long term fire history by analyzing four cores from the yangtze river delta yrd area east asia representing 8 0 ma and three sites in inner asia representing 18 2 ma the results show that the i mc remained higher during the relatively dry late holocene glacial stages than that during the humid middle holocene interglacial stages at individual sites ii mc increased with time in both inner asia and east asia after 18 and 8 ma respectively and iii mc always remained higher in the dry inner asia than in the contemporaneous wet east asia all these characteristics imply that late cenozoic fire occurrence in mid latitude asia experienced a gradual increasing trend along with the global temperature ice volume change and indicates a continuous aridification trend across mid latitude asia the global cooling rather than the tibetan plateau uplift might have played a key role in this observed trend c 2016 elsevier ltd all rights reserved

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

lake surface fluctuations since the late glaciation at lake daihai north central china a direct indicator of hydrological process response to east asian monsoon climate abstract sediment retrieved by coring from the center of enclosed lake daihai in north central china and lacustrine sediments obtained from lake terrace outcrops were employed to reconstruct the lake surface fluctuations and the relationships with monsoon climate since the late glaciation based on accelerator mass spectrometry ams radiocarbon chronology before ca 13 ka bp the surface of the lake was lower indicating a deficiency of effective precipitation and dry climate the result of relatively decreased monsoon precipitation during ca 13 11 ka bp the lake surface ascended to a relatively higher level marking a significant increase of effective precipitation the climate became humid indicating strengthened monsoon rainfall then the lake surface experienced a sharp decline ca 11 10 ka bp this could suggest a severe reduction of effective monsoon precipitation and drier climate ca 10 9 0 ka bp the lake surface area expanded temporarily as the level rose denoting the amelioration of monsoon related effective precipitation and a relatively humid climate subsequently the lake surface declined at ca 9 0 7 3 ka bp reflecting the prevalence of dry climate and relatively decreased monsoon precipitation higher lake level and larger lake depth indicated large scale expansion of the lake surface at ca 7 3 3 2 ka bp despite some secondary fluctuations this implied plentiful monsoon related effective precipitation and more humid climate in the lake basin since ca 3 2 ka bp the lake surface has experienced a severe fall except for a minor rise around 2 0 ka bp indicating dry climate as a whole from waning monsoon precipitation and relatively increased evaporation the effective precipitation variations revealed by lake surface fluctuations in lake daihai since the late glaciation are not only related to forcing factors such as insolation and temperature driven air masses from the continent and the ocean but are also influenced by regional feedback from topography vegetation coverage and hydrological status

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

impact of the doppler spread parameterization on the simulation of the middle atmosphere circulation using the ma echam4 general circulation model the zonal mean circulation of the middle atmosphere simulated by a general circulation model that includes the doppler spread parameterization of gravity wave momentum deposition is presented to illustrate the impact of the parameterization this simulation is compared to another obtained by using rayleigh friction instead it is found that the doppler spread parameterization improves the extratropical zonal mean circulation in the mesosphere by reducing the strength of the zonal winds above the jet maximum the parameterization also improves the simulation of the equatorial semiannual oscillation in the zonal mean zonal wind at the stratopause by enhancing the eastward phase and its downward propagation

effects of incomplete parameterization on full wavefield viscoelastic seismic data for petrophysical reservoir properties in inversion of viscoelastic full wavefield seismic data the choice of model parameterization influences the uncertainties and biases in estimating seismic and petrophysical parameters using an incomplete model parameterization results in solutions in which the effects of missing parameters are attributed erroneously to the parameters that are included incompleteness in this context means assuming the earth is elastic rather than viscoelastic the inclusion of compressional and shear wave quality factors qp and qs in inversion gives better estimates of reservoir properties than the less complete elastic model parameterization qp and qs are sensitive primarily to fluid types and saturations the parameter correlations are sensitive also to the model parameterization as noise increases in the viscoelastic input data the resolution of the estimated parameters decreases but the parameter correlations are relatively unaffected by modest noise levels

a holocene pollen record from the northwestern himalayan lake tso moriri implications for palaeoclimatic and archaeological research this paper presents a new fossil pollen record from tso moriri 32 54 n 78 19 e 4512 m a s l and seeks to reconstruct changes in mean annual precipitation map during the last 12 000 years this high alpine lake occupies an area of 140 km2 in a glacial tectonic valley in the northwestern himalaya the region has a cold climate with a map 300 mm and open vegetation the hydrology is controlled by the indian summer monsoon ism but winter westerly associated precipitation also affects the regional water balance results indicate that precipitation levels varied significantly during the holocene after a rapid increase in map a phase of maximum humidity was reached between ca 11 and 9 6 cal ka bp followed by a gradual decline in map this trend parallels the reduction in the northern hemisphere summer insolation comparison of different palaeoclimate proxy records reveal evidence for a stronger holocene decrease in precipitation in the northern versus the southern parts of the ism domain the long term trend of ism weakening is overlaid with several short periods of greater dryness which are broadly synchronous with the north atlantic cold spells suggesting reduced amounts of westerly associated winter precipitation compared to the mid and late holocene it appears that westerlies had a greater influence on the western parts of the ism domain during the early holocene during this period the westerly associated summer precipitation belt was positioned at mediterranean latitudes and amplified the ism derived precipitation the tso moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient harappan civilisation which flourished in the greater indus valley from approximately 5 2 to 3 cal ka bp the prolonged holocene trend towards aridity punctuated by an interval of increased dryness between ca 4 5 and 4 3 cal ka bp may have pushed the mature harappan urban settlements between ca 4 5 and 3 9 cal ka bp to develop more efficient agricultural practices to deal with the increasingly acute water shortages the amplified aridity associated with north atlantic cooling between ca 4 and 3 6 and around 3 2 cal ka bp further hindered local agriculture possibly causing the deurbanisation that occurred from ca 3 9 cal ka bp and eventual collapse of the harappan civilisation between ca 3 5 and 3 cal ka bp

holocene wildfires related to climate and land use change over the weihe river basin china abstract charcoal particles preserved in the loess palaeosol profiles provide records of wildfires during the holocene total organic carbon magnetic susceptibility and charcoal analysis and osl dating were carried out in the holocene loess palaeosol profiles at two sites in the weihe river basin the analytical results show that natural wildfires occurred frequently during the last glaciation when climate was dominated by northwest continental monsoon and steppe vegetation expanded southerly to the weihe river basin wildfire occurrence decreased during climatic amelioration in the early holocene during the holocene climatic optimum between 8500 b p and 3100 b p natural wildfire occurrence was reduced greatly pedogenic alteration to the accumulated dust was intensified because of the humid warm climate brought on by southeast maritime monsoon localized fire events in connection with human activities of the neolithic occurred in several episodes over the region during the late holocene when climate become drier wildfire occurrence over the upland hills shows a pattern different from that in the guanzhong basin over the upland hills in the north charcoal concentrations show a decreasing trend in the recent loess and topsoil it indicates infrequent biomass burning during the last 3100 years this is attributable to nomadic occupation of the loess hills during the bronze age and the development of a land use pattern of livestock farming in most part of the history over the loess tableland in the guanzhong basin in the south abruptly increased charcoal concentrations in the recent loess and topsoil show very high level of biomass burning this is attributable to the increasingly intensified land reclamation for cereal cultivation from the bronze age this study provides new insights into wildfires over the semi arid and sub humid regions in connection with climate and land use change

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

wave attenuation attributes as flow unit indicators in this article we present a model based interpretation algorithm to predict attenuation signatures associated with a reservoir s structure and its intrinsic properties scattering losses are caused by multiple reflections associated with the impedance contrast between different reservoir boundaries intrinsic losses are due to the fluids in the reservoir the rock fabric and the anisotropy due to vertical fractures because amplitude data are sensitive to these reservoir characteristics we calculate the wave attenuation response of the reservoir in the frequency range of surface seismic vsp crosswell seismic and borehole sonic a model of a plane wave traveling in a poroelastic multilayer earth medium allows us to include anisotropy the multilayer part of the model simulates elastic scattering the poroelastic part of the model simulates fluid flow effects in the reservoir and the anisotropic part of the model simulates reservoir fractures

the influences of zonal flow on wave breaking and tropical extratropical interaction in the lower stratosphere abstract the influences of the zonal mean flow on rossby wave breaking and tropical extratropical interaction in the lower stratosphere are investigated using a high resolution barotropic model it is found that the zonal mean wind in the subtropics of the winter hemisphere denoted as 30 is pivotal to the location and intensity of rossby wave breaking when 30 is positive and relatively large significant wave breaking occurs in two regions one in the midlatitudes of the winter hemisphere and the other in the tropics when 30 is small or negative on the other hand wave breaking occurs primarily in the middle to high latitudes of the winter hemisphere it is also found that when 30 is large wave breaking is sensitive to the phase of the equatorial quasi biennial oscillation qbo in that if the qbo is westerly significant wave breaking takes place in the midlatitudes of the winter hemisphere and the subtropics of the summer hemisphere and no wave breaking occurs in the equatorial region and

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

natural and anthropogenic forest fires recorded in the holocene pollen record from a jinchuan peat bog northeastern china abstract pollen and charcoal particles from a jinchuan peat northeastern china were examined to investigate the fire origin and interaction between climate vegetation fire and human activity during the holocene pollen results show that i a broadleaved deciduous forest was dominant during the early holocene ii from 5500 cal yr b p there was a gradual increase in coniferous trees mainly pinus and a decrease in broadleaved deciduous trees e g quercus juglans and ulmus zelkova iii after 4200 cal yr b p the deciduous forest was replaced by a mixed forest of coniferous and deciduous trees iv coniferous trees including pinus abies and picea further increased after 2000 cal yr b p reflecting a cooler and drier climate after 5500 4200 cal yr b p two layers of abundant microfossil charcoal particles 250 10 m and the coexistence of macrofossil particles 2 mm suggest two local fires fire event 1 5120 66 cal yr b p and fire event 2 1288 8 cal yr b p ad 662 8 charcoal layer 1 with a large amount of monolete psilate spores is superimposed on the long term trend of vegetation changes indicating a natural origin for fire event 1 that was probably facilitated by drying environmental conditions since the mid holocene cerealia type pollen and a low percentage of monolete psilate spores were observed in charcoal layer 2 indicating that fire event 2 was caused by clearing we suggest that fire event 2 may be related to the spread of the han farming culture accompanied by the territorial expansion of the tang dynasty to the studied area in ad 668

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

effects of the quasi biennial oscillation on low latitude transport in the stratosphere derived from trajectory calculations 1 the quasi biennial oscillation qbo of stratospheric zonal winds induces a secondary meridional circulation smc consisting of qbo variations in meridional and vertical winds in this work we investigate how these instantaneous meridional circulation anomalies add over time to variations of stratospheric transport to that end we compute backward parcel trajectories on the basis of the output of a chemistry climate model ccm at the equator the trajectories show the strongest vertical parcel displacement over a seasonal timescale when the qbo progresses toward easterly phase in the middle stratosphere during the solstitial seasons a large number of parcels come from the summer hemisphere causing in addition a qbo variation in the spread of the total ascent among equatorial parcels a qbo effect on meridional transport is diagnosed from pv gradients during summer in the easterly phase of the qbo which suggests a variation of the tropical subtropical barrier strength analyses of the parcel trajectories and ccm trace gas distributions confirm this finding we suggest that this variation is due to the combined effects of qbo and annual variation in meridional advection and in wave induced eddy transport

a seasonal climatology of effective diffusivity in the stratosphere a 7 year 1992 1998 seasonal climatology of effective horizontal diffusivity is presented for the stratosphere 350 1900 k as in previous studies the diagnosis is based on the equivalent length of a test tracer advected on isentropic surfaces in this case using the van leer flux limiting scheme driven by the united kingdom meteorological office assimilated winds although the magnitude of equivalent length is resolution dependent its structure is shown to be reasonably robust for quantifying the inhomogeneous mixing in the stratosphere the van leer calculation agrees well with a more expensive spectral transform calculation at a comparable resolution suggesting that the diagnostic is not sensitive to the advection scheme or subgrid representation of the models a first attempt is also made at estimating the implicit numerical diffusion of the van leer scheme which is necessary to convert equivalent length to effective diffusivity compared with the spectral calculations with a constant diffusion coefficient the van leer results show notably greater diffusivity within the winter polar vortices despite the comparable equivalent lengths suggesting that the scheme may be overdiffusing in the vicinities of mobile tracer extrema the climatology of equivalent length is then presented and the seasonal evolution is discussed in detail for the lower middle and upper stratosphere the major mixing barriers winter and summer polar vortices and tropical eddy transport barrier are easily identified as well as the strong mixing regions surf zones generally equivalent length tends to be small in regions of strong zonal wind and large in regions of weak wind large values of equivalent length are observed in the summer lower stratosphere and in the middle stratosphere during the breakup of the polar vortices interhemispheric asymmetry is observed both after the winter polar vortex breakup where in the middle stratosphere the southern hemisphere shows much larger equivalent lengths and in the summer tropical region where larger equivalent lengths are observed in the northern hemisphere likely related to the monsoon circulation a monthly averaged equivalent length climatology is presented and implications for two dimensional stratospheric chemistry transport modeling are discussed

charcoal records of fire history in the holocene loess soil sequences over the southern loess plateau of china abstract charcoal preserved in accretionary loess soil profiles within the southern part of the loess plateau has recorded fire history and landscape evolution connected with climatic variations and human activities local wildfires occurred frequently during the late last glacial period and the early holocene before 8500 years bp when steppe vegetation expanded from the inner mongolian plateau southerly over the loess plateau during the holocene climatic optimum between 8500 years bp and 3100 years bp natural wildfires were largely reduced pedogenesis of the luvisols and isohumisols was intensified because of the increased monsoonal precipitation and soil moisture localized fires in connection with human activities occurred in different patterns at the study sites fire seems to have been applied to vegetation clearance for land reclamation for millet cultivation at many places during the neolithic and early bronze age levels of biomass burning were very high during the late holocene when the climate became drier and historical land use became more intensive at some sites the intensity of human disturbance by fire and cultivation increased continuously during the last 3100 years at the other sites local fires occurred most frequently between 3100 years bp and 1500 years bp during the major period of land reclamation for cereal cultivation human burning of the landscape has been reduced since then

modeling the quasi biennial oscillation s influence on isentropic tracer transport in the subtropics tracer transport in the lower stratosphere is investigated using an off line semi lagrangian transport model and winds from a mechanistic three dimensional middle atmosphere model interpolated to the 650 k isentropic surface over a winter season by comparing two simulations the effect of the quasi biennial oscillation s qbo s easterly or westerly wind phases on low latitude transport is examined especially regarding the formation of an apparent subtropical transport barrier at the equatorward edge of the surf zone the tracer field is diffused less than potential vorticity pv and shows sharper gradients and finer structures developing over the winter in both qbo phases the winter extratropical surf zone is bounded by large tracer gradients equatorward of about 15 latitude the inability of quasi stationary rossby waves to propagate into qbo easterlies leads to a much sharper edge forming between the rapidly stirred extratropical surf zone and the relatively unstirred tropics during the easterly qbo phase than occurs during the westerly qbo phase in the westerly phase some rossby wave activity can propagate across the equatorial westerlies and break on reaching the summer hemisphere easterly winds causing mixing there simulations using a tracer initially confined to the tropics show that more tropical air is mixed out to the winter extratropics by rossby wave stirring when the qbo phase is easterly despite the sharper band of stronger tracer or pv gradient which separates the tropics and the winter extratropics in this phase while air was mixed out of the tropics in both qbo phase simulations neither qbo phase simulation showed extratropical air being irreversibly mixed into the tropics these results are related to observations of the tropical reservoir of stratospheric aerosols especially the dynamics and transport of its winter hemisphere boundary

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

holocene fire on the northeast tibetan plateau in relation to climate change and human activity abstract a series of holocene charcoal concentrations cc records from a slope sedimentary section in gonghe basin northeast tibetan plateau are analyzed to investigate fire characteristics e g frequency or magnitude and their linkages with paleoclimate change and ancient human activities the results reveal that changes in fire indicators are well correlated with paleoclimatic change during the past 10 0 ka bp this pattern is characterized by lower cc in the warm and humid middle holocene and higher total cc in the cold dry climate of the early and late holocene meanwhile an event characterized by abnormally high cc values at 3 6 ka bp distinct from the above trend indicates an anomalously high fire frequency which cannot easily be explained as the result of a climatic event alternatively this event is noted to correspond closely with the time of rapid human occupation of the high elevation tibetan plateau many basic domestic and agricultural activities e g slash and burn farming cooking or heating have required fire in the hostile environment of the tibetan plateau this is reflected in the higher cc following the spread of human habitation the analysis of cc might be a useful alternative method for investigating human activities when no direct evidence is available in the holocene tibetan plateau records

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

holocene treeline shifts and monsoon variability in the hengduan mountains southeastern tibetan plateau implications from palynological investigations abstract the upper 8 45 m of a sediment core from lake naleng were analysed for its pollen and charcoal content to detect vegetation climate and human activity changes on the southeastern tibetan plateau tp since the pleistocene holocene transition 11 7 cal kyr bp the application of pollen indicator taxa pollen sums biomisation and multivariate analysis helped to reconstruct environmental conditions during the holocene furthermore 64 surface samples from the southeastern tp and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation the modern vegetation was recorded in the surface pollen assemblages by pollen indicator types although sediments also contain pollen spectra extra regional pollen transported from lower vegetation belts which is seen as a consequence of steep elevation gradients at the southeastern margin of the tp the relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the holocene record spreading of forests at the beginning of the holocene marks the transition to warmer conditions from 10 7 to 4 4 cal kyr bp open abies betula forests were found at lake naleng probably reflecting a stronger than present summer monsoon temperature range reconstructions suggest a temperature that was about 2 3 c warmer and a treeline position that was 400 600 m higher than today a severe climate deterioration with temperatures about 1 2 c colder than before is documented by a retreating forest between 8 1 and 7 2 cal kyr bp forests retreated while subalpine rhododendron shrubs spread around lake naleng indicating colder conditions with temperatures 1 2 c below early and mid holocene level after 4 4 cal kyr bp the forest decline at 4 4 cal kyr bp is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human induced fires as reason for the forest retreat however grazing indicators imply human influence on the environment since 3 4 cal kyr bp around lake naleng we therefore consider the rapid treeline shift seen at 3 4 cal kyr bp as partly generated by human activity and partly by climatic conditions

how old is the human footprint in the world s largest alpine ecosystem a review of multiproxy records from the tibetan plateau from the ecologists viewpoint the age at which a human environment was made is strongly debated in quaternary science the perception of the human footprint requires an understanding of the contrast between the present cultural environment and the natural vegetation this is especially true for high altitude ecosystems such as the world s largest alpine ecosystem the 450 000 km 2 of golf course like pastures dominating the southeastern tibetan plateau this ecosystem is widely considered to be natural but only because of the unawareness of the effects of grazing management and the incorrect assessment of human signals in palaeo proxies here we posit the hypothesis that this ecosystem is a human induced replacement to test our hypothesis against defined a priori criteria we 1 monitored vegetation in grazing exclosures 2 produced floristically complete vegetation records 3 compared the vegetation records with data of the nearest climate stations 4 surveyed forest and experimental reforestation trials with endemic tree species 5 analyzed pollen and re evaluated published pollen diagrams and 6 integrated these results with palaeopedological and anthracological results of previous studies the results of long term grazing exclosure experiments the prevalence of grazing adapted plant functional types the occurrence of isolated vigorous forests in alpine pastures and the successful reforestation trials in presently treeless pastures together suggest that dominant pastures replaced forests in the montane belt and tall grassland in the alpine belt the spatial and temporal coincidence of palaeosols and archaeological sites with tree species charcoal the decline in forest pollen during the mid holocene climatic optimum and the first appearance of human indicator pollen are most parsimoniously explained by the early presence of foragers and pastoralists the onset of pastoralism in the tibetan highlands is presumed to date from the 8th millennium bp c 2013 elsevier ltd all rights reserved

reconstructing holocene vegetation and climate history of nam co area tibet using pollen and other palynomorphs abstract a drill core 1 8 m 34 samples was taken out of a swamp near nam co tibet china for palynological analysis c14 dating of the cores sediment at 3 different layers led to an numerical core age of about 8000 bp and the palynomorph content of prepared samples enabled reconstruction of the vegetation and climatic history of nam co area pollen of alpine steppe elements together with cyperaceae dominates the palynoflora reflecting the existing vegetation units around the lake throughout the investigated time span due to availability of water precipitation the different vegetation units extended or had to retreat and hence the amount of their pollen increased or decreased the presence of arboreal plants verified by charcoal particles suggest the existence of woodlands in the lake s surrounding area until possibly human made fires changed the environment over time holocene climate history around nam co shows several phases of a strengthening weakening or even an interruption of monsoonal activity changing conditions between dry and humid evolved from 8017 bp until 4800 bp a mostly humid and relative stable system occurred from 4800 until 700 bp whereas the last 700 years are characterized by drier conditions according to fluctuating monsoonal activity humid or arid periods have been different in duration and intensity the interaction of both parts of the monsoonal system the south asian monsoon and the east asian monsoon influenced the climatic conditions around nam co

improving q estimates from seismic reflection data using well log based localized spectral correction most methods for deriving q from surface seismic data depend on the spectral content of the reflection the spectrum of the reflected wave may be affected by the presence of thin beds in the formation which makes q estimates less reliable we incorporate a method for correcting the reflected spectrum to remove local thin bed effects into the q versus offset qvo method for determining attenuation from seismic reflection data by dividing the observed spectrum by the local spectrum of the known reflectivity sequence from a nearby well log we obtain a spectrum more closely resembling that which would be produced by a single primary reflector this operation equivalent to deconvolution in the time domain is demonstrated to be successful using synthetic data as a test case we also apply the correction method to qvo with a real seismic line over a south florida site containing many thin sandstone and carbonate beds when corrected spectra are used there is significantly less variance in the estimated q values and fewer unphysical negative q values are obtained based on this method it appears that sediments at the florida site have a q near 33 that is roughly constant from 170 to 600 m depth over the length of the line

determination of black carbon by chemical oxidation and thermal treatment in recent marine and lake sediments and cretaceous tertiary clays abstract several sample treatments and analytical methods for the measurement of black carbon in a wide variety of sediments were considered in which the removal of organic carbon is a critical step in the procedure a comparison between chemical oxidation and thermal treatment was conducted and the latter was shown to be inappropriate due to the polymerisation of organic matter using acid dichromate oxidation reactive kerogen was separated from black carbon in a variety of lake and marine and recent and ancient sediments with relatively small and quantifiable losses 1 6 of black carbon under carefully controlled reaction conditions

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi

holocene changes in fire frequency in the daihai lake region north central china indications and implications for an important role of human activity abstract black carbon bc content in a sediment core from daihai lake inner mongolia was analyzed to reconstruct a high resolution history of fires occurring in northern china during the holocene and to examine the impacts of natural changes and human activities on the fire regime the black carbon mass sedimentation rate bcmsr was disintegrated into two components the background bcmsr and the bcmsr peak with the bcmsr peak representing the frequency of fire episodes both the background bcmsr and the magnitude of the bcmsr peak display a close relation with the percentage of tree pollen from the same sediment core suggesting that regional vegetation type would be a factor controlling the intensity of fires the inferred fire episode frequency for the holocene exhibits two phases of obvious increases i e the first increase from

black carbon records in chinese loess plateau over the last two glacial cycles and implications for paleofires abstract to study the temporal and spatial changes in paleofires over the chinese loess plateau black carbon concentrations were analyzed on the loess paleosol samples from three sections along a north south transect using the orbitally tuned time scales of the sections the black carbon mass sedimentation rates bcmsr were calculated results show that in the last two glacial cycles the bcmsr values in glacial periods are 2 3 times higher than in interglacial periods and the bcmsr variability has a relatively strong precession associated 23 ky period suggesting that the glacial cold dry climate conditions were apt to induce natural fires over the loess plateau comparison of the bcmsr records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern loess plateau than in the southern part coinciding with the previous conclusion that the northern plateau has experienced a drier climate regime in both glacial and interglacial periods the substantial increase in bcmsr of the upper s0 relative to the lower s0 at lingtai and weinan indicates that human activities have exerted a significant influence on fire regimes in the middle and southern loess plateau during late holocene due to the relatively intensive agricultural usage of land

on the subtropical edge of the stratospheric surf zone abstract the formation of a subtropical transport barrier in the wintertime stratosphere is investigated in the context of a high resolution shallow water model in which rossby waves are topographically forced on a zonally symmetric basic state two sets of experiments are performed in the first adiabatic set no dissipation or forcing of the mean state is imposed in the second set the layer thickness is relaxed to an equilibrium state taken to be representative of middle stratospheric radiative equilibrium temperatures it is found that in the adiabatic case only a very weak subtropical barrier forms for forcing amplitudes that generate realistically steep potential vorticity gradients at the edge of the polar vortex the vigorous wave breaking in the surf zone generates secondary waves that spread and in turn break well into the summer hemisphere in contrast the inclusion of relaxation to a realistic thermal equilibrium leads to the formation of a subtropical region of steep pv gradients the

seasonal variation of isentropic transport out of the tropical stratosphere the seasonal variation of the isentropic transport out of the tropical stratosphere is examined using contour advection calculations with winds from meteorological analyses for the period july 1991 to june 1994 calculations using winds from three different meteorological analyses are compared there is good qualitative agreement between the different calculations for extratropical structures but not for structures in the tropics there is also reasonable agreement between area diagnostics for transport out of the tropics derived from these calculations transport out of the tropics occurs in rossby wave breaking events in which filaments of tropical air are drawn into middle latitudes in all years these wave breaking events occur during the fall to spring period when there are westerlies throughout middle latitudes late september to early may in the northern hemisphere this includes periods before the formation of and after the breakup of the polar vortex in the northern hemisphere the rate of transport out of the tropics during fall to spring fluctuates around a constant value whereas in the southern hemisphere there is a relatively quiet midwinter period with maxima in the transport in early and late winter