palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

temporal variations of accumulation and temperature during the past two centuries from belukha ice core siberian altai 1 the temporal variation of accumulation and temperature in the siberian altai were investigated using a 86 m long ice core from belukha glacier 49 48 26 n 86 34 43 e 4062 m a s l covering the time period 1816 to 2001 as temperature sensitive parameters the melt percent profiles and the stable oxygen isotopes 18o were evaluated representing summer season and march to november temperatures respectively the accumulation record showed no long term trend and only minor deviations of limited duration from the accumulation average of 0 5 m water equivalent y weq y were observed in contrast the two temperature proxies indicate a strong warming trend in the order of 1 6 0 4 c and 1 7 1 1 c over the last century inferred from melt percentages and the 18o record respectively and 2 5 1 7 c since the mid 19th century inferred from the 18o record this reflects an amplified regional climate response following the little ice age lia as compared to the northern hemisphere average most probably caused by the strong continentality of the siberian altai region the sudden onset of large melt features since 1988 indicates that the upper reaches of belukha glacier are experiencing a change from the recrystallization to the cold infiltration zone that now allows for multiannual percolation of meltwater implying that the conservation of accumulation and geochemical properties including those providing temperature proxies is currently endangered

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

a record of holocene climate change from lake geochemical analyses in southeastern arabia lacustrine sediments from southeastern arabia reveal variations in lake level corresponding to changes in the strength and duration of indian ocean monsoon iom summer rainfall and winter cyclonic rainfall the late glacial holocene transition of the region was characterised by the development of mega linear dunes these dunes became stabilised and vegetated during the early holocene and interdunal lakes formed in response to the incursion of the iom at approximately 8500 cal yr bp with the development of c3 dominated savanna grasslands the iom weakened ca 6000 cal yr bp with the onset of regional aridity aeolian sedimentation and dune reactivation and accretion despite this reduction in precipitation the lake was maintained by winter dominated rainfall there was a shift to drier adapted c4 grasslands across the dune field lake sediment geochemical analyses record precipitation minima at 8200 5000 and 4200 cal yr bp that coincide with bond events in the north atlantic a number of these events correspond with changes in cultural periods suggesting that climate was a key mechanism affecting human occupation and exploitation of this region

stable isotope time series and precipitation origin from firn core and snow samples altai glaciers siberia in the summers of 2001 and 2002 glacio climatological research was performed at 4110 4120ma s l on the belukha snow firn plateau siberian altai hundreds of samples from snow pits and a 21m snow firn core were collected to establish the annual seasonal monthly depth accumulation scale based on stable isotope records stratigraphic analyses and meteorological and synoptic data the fluctuations of water stable isotope records show well preserved seasonal variations the d 18 o and dd relationships in precipitation snow pits and the snow firn core have the same slope to the covariance as that of the global meteoric water line the origins of precipitation nourishing the belukha plateau were determined based on clustering analysis of d 18 o and d excess records and examination of synoptic atmospheric patterns calibration and validation of the developed clusters occurred at event and monthly timescales with about 15 uncertainty two distinct moisture sources were shown oceanic sources with d excess 12 two thirds of the annual accumulation was from oceanic precipitation of which more than half had isotopic ratios corresponding to moisture evaporated over the atlantic ocean precipitation from the arctic pacific ocean had the lowest deuterium excess contributing one tenth to annual accumulation

snow accumulation rate on qomolangma mount everest himalaya synchroneity with sites across the tibetan plateau on 50 100 year timescales annual layer thickness data spanning ad 1534 2001 from an ice core from east rongbuk col on qomolangma mount everest himalaya yield an age depth profile that deviates systematically from a constant accumulation rate analytical model the profile clearly shows that the mean accumulation rate has changed every 50 100 years a numerical model was developed to determine the magnitude of these multi decadal scale rates the model was used to obtain a time series of annual accumulation the mean annual accumulation rate decreased from 0 8m ice equivalent in the 1500s to 0 3m in the mid 1800s from 1880 to 1970 the rate increased however it has decreased since 1970 comparison with six other records from the himalaya and the tibetan plateau shows that the changes in accumulation in east rongbuk col are broadly consistent with a regional pattern over much of the plateau this suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area however a record from dasuopu only 125 km northwest of qomolangma and 700 m higher than east rongbuk col shows a maximum in accumulation during the 1800s a time during which the east rongbuk col and tibetan plateau ice core and tree ring records show a minimum this asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology

a record of holocene summer climate from a canadian high arctic ice core melt layers in ice cores are formed by melting on the snow pack surface which produces water that percolates down and refreezes in the colder snow layers below melt layers are distinguished by their bubble texture because more ice forms in the snow pack in warm summers than in cool summers the changing concentration with depth of melt layers in snow pits1 2 and ice cores3 5 is an indicator of past summer climate here we report on studies of melt layers in two canadian high arctic surface to bedrock ice cores although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40 of the total climatic signal recorded in the melt layers we interpret their varying concentrations in terms of changing summer temperatures over the past 10 000 years the warmest summers occurred 8 10 kyr ago and the coldest only 150 years ago the summers over the past 100 years have been the warmest for more than 1 000 years but are still not as warm as those of the early holocene the melt layer record is in broad agreement with geological records of glacier retreat during the holocene6 8 indicating that these data also contain information of regional significance

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

the north atlantic oscillation signature in deuterium and deuterium excess signals in the greenland ice sheet project 2 ice core 1840 1970 the greenland ice sheet project 2 gisp2 core can enhance our understanding of the relationship between parameters measured in the ice in central greenland and variability in the ocean atmosphere and cryosphere of the north atlantic ocean and adjacent land masses seasonal summer winter to annual responses of d and deuterium excess isotopic signals in the gisp2 core to the seesaw in winter temperatures between west greenland and northern europe from a d 1840 to 1970 are investigated this seesaw represents extreme modes of the north atlantic oscillation which also influences sea surface temperatures ssts atmospheric pressures geostrophic wind strength and sea ice extents beyond the winter season temperature excursions inferred from the d record during seesaw extreme nao mode years move in the same direction as the west greenland side of the seesaw symmetry with the west greenland side of the seesaw suggests a possible mechanism for damping in the ice core record of the lowest decadal temperatures experienced in europe from a d 1500 to 1700 seasonal and annual deuterium excess excursions during seesaw years show negative correlation with d this suggests an isotopic response to a sst land temperature seesaw the isotopic record from gisp2 may therefore give information on both ice sheet and sea surface temperature variability cross plots of d and d show a tendency for data to be grouped according to the prevailing mode of the seesaw but do not provide unambiguous identification of individual seesaw years a combination of ice core and tree ring data sets may allow more confident identification of ga and gb extreme nao mode years prior to 1840

abrupt and moderate climate changes in the mid latitudes of asia during the holocene a multiple parameter dating technique was used to establish a depth age scale for a 171 3 m 145 87 m w e surface to bedrock ice core bl2003 recovered from the cold recrystallization accumulation zone of the western belukha plateau 4115 m a s l in the siberian altai mountains the ice core record presented visible layering of annual accumulation and of delta o 18 delta d stable isotopes and a clear tritium reference horizon a steady state glacier flow model for layer thinning was calibrated and applied to establish a depth age scale four radiocarbon c 14 measurements of particulate organic carbon contained in ice core samples revealed dates for the bottom part of bl2003 from 9075 1221 cal a bc at 145 2 0 1 m w e 0 665 m w e from the bedrock to 790 93 ad at 121 1 m w e depth sulfate peaks coincident with volcanic eruptions the tunguska meteorite event and the 1842 dust storm were used to verify dating analysis of the bl2003 ice core reveals that the modern altai glaciers were formed during the younger dryas yd similar to 10 950 to similar to 7500 cal a bc and that they survived the holocene climate optimum hco similar to 6500 to similar to 3600 cal a bc and the medieval warm period mwp similar to 640 to similar to 1100 ad a decrease in air temperature at the beginning and an abrupt increase at the end of the yd were identified intensification of winds and dust loading related to asian desert expansion also characterized the yd during the yd major ion concentrations increased significantly up to 50 times for na background up to 45 times for ca2 and mg2 and up to 20 times for so42 relative to the recent warm period from 1993 to 2003 a warm period lasted for about three centuries following the yd signaling onset of the hco a significant and prolonged decrease in air temperature from similar to 2000 to similar to 600 cal a bc was associated with a severe centennial drought scd a sharp increase in air temperatures after the scd was coincident with the mwp after the mwp a cooling was followed gradually with further onset of the little ice age during the modern warm period 1973 2003 an increase in air temperature is noted which nearly reaches the average of hco and mwp air temperature values

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

deformation in the vicinity of ice divides calculs numeriques aux elements finis de la variation de la vitesse horizontale avec la profondeur au voisinage d une difference de la glace symetrique isotherme et ou glissement sur un lit plat

greenland ice core signal characteristics an expanded view of climate change the last millenium of earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity we have analyzed the major ions contained in the greenland ice sheet project 2 gisp 2 ice core from the present to 674 a d to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling volcanic emissions sea salt and terrestrial influences we have adapted and extended mathematical procedures for extracting sporadic e g volcanic events secular trends and periodicities found in the data sets finally by not assuming that periodic components signals were stationary and by utilizing evolutionary spectral analysis we were able to reveal periodic processes in the climate system which change in frequency turn on and turn off with other climate transitions such as that between the little ice age and the medieval warm period

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

climate changes in east europe and siberia at the late glacial holocene transition abstract the main climatic oscillations of the lateglacial early holocene allerod younger dryas and preboreal can be distinguished all over eastern europe and siberia distribution of the main climatic indices in the lateglacial early holocene from west to east in northern eurasia shows that variations of the mean january temperature t jan o were larger than those of july temperature t july o as at present t jan o decreased to the east while the deviations from the present day values were greater in the west during the younger dryas the seasonality of climate increased considerably especially in the western european part of the studied area the greatest negative temperature deviations from the present day values up to 14 c occurred in the northwestern part of the east european plain near the scandinavian ice sheet it can be explained by a cooling influence from the remaining large ice body accordingly with degradation of the ice sheet at the warmer intervals of the lateglacial and early holocene the regional differences in temperature deviations became smaller up to 8 c on the whole precipitation p decreased in an easterly direction though its deviations from the modern level varied for different time intervals during the younger dryas p amounted to 60 65 of the present day values in the east european plain 80 in central west siberia and only 50 in central yakutia for the entire northern eurasia p did not exceed 300 350 mm yr in yakutia it was only 100 mm yr levels typical for present day dry steppe and semidesert zones nevertheless the reconstructed changes of the main climatic indexes were proportional to the present day climatic characteristics so that the general tendencies of their contemporary distribution in the mid latitudes were preserved during the entire lateglacial early holocene interval this shows that the general circulation of the atmosphere and geographical distribution of the main highs and lows in the studied time interval were in essence similar to the present day ones boundaries of permafrost in lateglacial and early holocene migrated in response to climate changes the southern limit of permafrost during the allerod was at 60 n in east europe and 55 n in west siberia during the younger dryas it moved south to 50 52 n in east europe and parabolic sand dunes were formed

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

recent changes of glacier coverage in the western terskey alatoo range kyrgyz republic using corona and landsat corona images from 1971 and a landsat image from 2002 are used to assess glacier variations in the last 30 years in the western terskey alatoo range a part of the tien shan in the northeast of the kyrgyz republic the glaciers have shrunk during this period the 269 mountain glaciers measured in the study area had an original combined area of 245 km 2 which has decreased 18 4 km 2 representing a loss of 8 of the original glacier coverage in 1971 individual glaciers covering 1 km 2 account for 28 of the combined glacial coverage but loss from these small glaciers represents 38 of the total decrease in area the relative change of area is larger for small scale glaciers and its contribution to shrinkage of glacier area is high this shrinkage has been linked to climate changes as recorded at local stations many small scale glaciers are distributed around issyk kul lake and rapid glacier reduction is expected in this area in the future

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

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

towards radiocarbon dating of ice cores a recently developed dating method for glacier ice based on the analysis of radiocarbon in carbonaceous aerosol particles is thoroughly investigated we discuss the potential of this method to achieve a reliable dating using examples from a mid and a low latitude ice core two series of samples from colle gnifetti 4450 m a s l swiss alps and nevado illimani 6300 m a s l bolivian andes demonstrate that the 14c ages deduced from the water insoluble organic carbon fraction represent the age of the ice sample sizes ranged between 7 and 100 g carbon for validation we compare our results with those from independent dating this new method is thought to have major implications for dating non polar ice cores in the future as it provides complementary age information for time periods not accessible with common dating techniques

temporal variations of mineral dust biogenic tracers and anthropogenic species during the past two centuries from belukha ice core siberian altai 1 in july 2001 a 140 m long ice core was recovered from the belukha glacier 49 48 26 n 86 34 43 e 4062 m a s l in the siberian altai the ion chemistry of the upper 86 m covering the last two centuries is characterized by biogenic emissions ammonium and formate aeolian dust calcium magnesium chloride and sodium and anthropogenic species sulfate nitrate and ammonium particularly high ammonium and formate concentrations indicate pronounced emissions from siberian forests the inferred fire frequency does not show a long term trend but distinct periods of enhanced activity sulfate has the highest industrial to preindustrial ratio and an anthropogenic contribution of more than 80 variations in this record reflect sulfur dioxide emissions in siberia and kazakhstan sulfate concentrations remained low until 1950 then sharply increased and peaked in the 1970s the decrease in the 1980s is attributed to the economic political and social crises and to the replacement of coal with gas rising nitrate concentrations since 1960 reflect traffic growth and enhanced fertilizer application increasing ammonium concentrations since the 1950s are attributable to population inflow in southern siberia with the associated enhancement of agricultural activity a nitrate peak of short duration in 1908 is thought to be the atmospheric signature from the tunguska event on 30 june 1908

monsoon and dust signals recorded in dasuopu glacier tibetan plateau during summer 1997 a 15 m firn core was recovered from dasuopu glacier 28 23 n 85 44 e 7000 m a s l on the northwest margin of xixabarngma feng in the central himalaya oxygen isotope values and concentrations of ca 2 mg 2 nh 4 so 4 2 and no 3 were measured over the 10 years of snow accumulation captured in the firn core the seasonal variations of 18 o values and major ion concentrations in the dasuopu core indicate that summer monsoon and dust signals are clearly recorded in dasuopu glacier annual variations in 18 o values are controlled by the amount effect with more negative i e lighter 18 o values representing summer monsoon precipitation characteristic of tropical regions higher concentrations of ca 2 mg 2 and so 4 2 reflect the influx of mineral aerosols from the vast arid and semi arid desert regions to the north and west during the spring dust storm period high spring concentrations of nh 4 and no 3 appear to reflect changes in regional biogenic source strength

the rates of sea salt sulfatization in the atmosphere and surface snow of inland antarctica 1 most of the aerosol particles present in the surface snow and ice of inland antarctica come from primary sea salt sodium chloride and marine biological activity methansulfonic and sulfuric acids melted water from surface snow firn and holocene ice contains mainly sodium chloride and sulfate ions although it is well known that sea salt aerosols react rapidly with sulfuric acid a process known as sulfatization it is not known when this process takes place in this research we undertake to measure the proportion of sea salt aerosols that undergo sulfatization in the atmosphere and surface snow as opposed to deeper ice in order to understand the suitability of sea salt aerosols as a proxy for past climates in deep ice cores we directly measure the sulfatization rates in recently fallen snow 0 4 m in depth collected at the dome fuji station using x ray dispersion spectroscopy to determine the constituent elements of soluble particles and computing the molar ratios of sodium chloride and sodium sulfate we estimate that about 90 of the initial sea salt aerosols sulfatize as they are taken up by precipitation over dome fuji or in the snowpack within one year after being deposited on the ice sheet

monitoring and prediction of shrinkage of a small glacier in the nepal himalaya in 1978 the first detailed glaciological studies were carried out on the small glacier ax010 in a glacier inventory of dudh kosi region in the nepal himalaya its length area and highest and lowest elevations in 1978 were 1 7 km 0 57 km2 5360 and 4950 m a s l respectively two resurveys of its terminus position and or surface elevations were carried out in 1989 and 1991 the glacier retreated by about 30 and 28 m during the periods 1978 89 and 1989 91 respectively in 1995 annual monitoring of this glacier by means of ground survey stake method and topographical mapping began in order to obtain its mass balance surface flow velocity and extent and link them with climatic conditions the results obtained in 1995 are summarized as follows 1 during the period 1991 95 the glacier retreated by 12 m 2 associated with the ice thickness loss in the lower part of the glacier the horizontal surface velocities along the center line in 1995 june october showed a remarkable decrease on the glacier tongue to about 50 of those in 1978 shrinkage of the glacier in the near future is predicted from a simple model calculation for the case that climatic conditions remain unchanged from 1995 the results show that the present shrinkage should continue and accelerate

estimating volume change of mountain glaciers using srtm and map based topographic data this paper describes a method for estimating the volume change of mountain glaciers using the shuttle radar topography mission srtm c band data 2000 and a digital elevation model dem generated from topographic maps this approach was developed with srtm data and topographic maps of 1 25 000 scale 1977 from the akshiirak glaciers tien shan central asia the dem for 1977 was generated using 10 m contour lines from 18 map sheets covering the akshiirak massif and surrounding area the nominal vertical accuracy of the maps is 3 3 m the standard deviation of the differences between the map derived dem and the srtm data on glacier free areas of less than 25deg is 6 3 m a single localized region in the western periphery of the study area with systematic error in the srtm data from 20 to 12 m on a 30 km spatial scale was found and excluded from the error analysis assuming a 10 m map error on the upper snow covered glacier areas the estimated root mean square error of the glacier surface change is 8 2 m from 1977 to 1999 the average glacier surface thinning is 15 1 m and the estimated volume loss is 6 15 km3 the rate of the akshiirak glacier volume loss has increased by 2 7 times compared with historical data from 1943 to 1977 the srtm data show an opportunity for quantifying climatic and dynamic surface elevation changes in mountain glaciers ice cloud and land elevation satellite icesat laser altimetry and srtm data could also be used for the estimation of short term surface changes of mountain glaciers

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

reevaluation of the reconstruction of summer temperatures from melt features in belukha ice cores siberian altai 1 in a previous study past summer temperatures were reconstructed from melt features in the belukha ice core siberian altai we evaluated the climatic representativeness of net accumulation and melt features by comparing two belukha ice cores retrieved at neighboring sites by different institutions and dated by different methods melt features in both cores showed a significant correlation but the trends of net accumulation were different between the cores melt features corresponded to the retreat rate of a glacier terminus in a neighboring mountain range these findings demonstrate the spatial representativeness of melt features in the ice cores we reevaluated an equation formulated for reconstructions of summer temperature as used in a previous study and found that it underestimates temperature we propose an alternative equation to obtain more reliable summer temperatures from melt features and net accumulation records for the period from 1914 to 2003

glacier retreat as a result of climate warming and increased precipitation in the tarim river basin northwest china the tarim river basin a river system formed by the convergence of nine tributaries is the most heavily glacierized watershed in arid northwest china in the basin there are 11 665 glaciers with a total area of 19 878 km 2 and a volume of 2313 km 3 glaciers in the basin play a significant role in the water resource system it is estimated that they provide about 133 10 8 m 3 of meltwater annually contributing 39 of the total river runoff under the influence of global warming northwest china has experienced a generally warmer and drier climate since the mid 19th century however a so called warm and wet transition has occurred since the late 1980s evidenced by an increase in both precipitation and stream discharge in the xinjiang autonomous region and neighboring regions this paper describes how glaciers in the tarim river basin have responded to such warming and increased precipitation and the impact of these glacier changes we analyzed the variations of more than 3000 glaciers since the 1960s using topographical maps high resolution satellite images and aerial photographs of the river basin our results indicate that glaciers in the basin have been mostly in retreat in the past 40 years and ice wastage has significantly influenced water resources in the tarim river basin estimation by a degree day meltwater model shows the positive anomaly in stream runoff of the tailan river can be partly attributed to the increase in glacier runoff amounting to one third of the stream discharge and a rough estimation using observed average ablation on the termini of 15 glaciers in china verifies that the mass loss calculated by a glacier area volume relation is reasonable 1 study area

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

extraordinary floods related to the climatic event at 4200 a bp on the qishuihe river middle reaches of the yellow river china abstract palaeo hydrological study was carried out in the qishuihe river valley in the middle reaches of the yellow river several bedsets of flood slackwater deposit were identified in the holocene loess soil sequences on the riverbanks they were differentiated from aeolian loess and soils by the parallel and waving beddings and the distinctive stratigraphic breaks separating individual palaeoflood events chronology of the flood events was established by osl dating checked by archaeological identification of the anthropogenic remains retrieved from the sequences the results show that successive floods occurred between 4300 and 4000 a bp in association with the abrupt climatic event of 4200 a bp these overbank floods had the riverbank settlement inundated repeatedly another series of extraordinary floods occurred between 3200 and 3000 a bp when monsoonal climate shifted from the mid holocene climatic optimum toward late holocene dry conditions the climatic event of 4200 a bp and the climatic decline at 3100 a bp were believed to be characterized by droughts previously this work provides solid evidence that both severe droughts and extreme floods were parts of the climatic variability during abrupt climatic event and climatic decline in the semi arid to sub humid zones over the world

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

variability of monsoon climate in east asia at the end of the last glaciation abstract high resolution paleomonsoon proxy records from peat and eolian sand paleosol sequences at the desert loess transition zone in china denote a rapid oscillation from cold dry conditions 11 200 10 60014c yr b p to cool humid conditions 10 600 10 20014c yr b p followed by a return to cold dry climate 10 200 10 00014c yr b p variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern asia during the younger dryas interval late glacial climate in the chinese desert loess belt that lies downwind from europe was strongly influenced by cold air from high latitudes and from the north atlantic via the westerlies the inferred precipitation variations were likely caused by variations in the strength of the siberian high which influenced the pressure gradient between land and ocean and therefore influenced the position of the east asian monsoon front

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

the retreat of glaciers in response to recent climate warming in western china glaciers in china are primarily located in the tibetan plateau tp and surrounding high mountains the chinese glacier inventory indicates that there are 46 377 glaciers in western china meteorological records indicate that air temperature in western china has risen by 0 2 c per decade since 1951 and 1998 was the warmest year precipitation in the region increased by 5 10 per decade from 1953 to 1997 using remote sensing and geographic information system methods we have monitored the changes in 5000 glaciers over the past 50 years we conclude that 80 of glaciers in western china have retreated losing 4 5 of their combined areal coverage although some glaciers have advanced in addition regional differences characterize glacier changes over the past few decades for example glaciers in the central and northwestern tp were relatively stable while glaciers in the mountains surrounding the tp experienced extensive wastage mass balance variations for some glaciers show accelerated ice shrinkage in the last two decades

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

a continuous multimillennial ring width chronology in yamal northwestern siberia remains of subfossil siberian larch trees in the holocene deposits of the yamal peninsula western siberia have been collected in order to develop a continuous multimillennium tree ring width chronology this work has produced a calendar age dated 4000 year 2000 bc to ad 1996 series from these data summer temperature variability in this region has been estimated on annual to multidecadal timescales radiocarbon dating of selected older material shows that the oldest subfossil wood is 9400 years old and the dates of the sampled material are generally distributed evenly through time it will therefore be possible to develop a tree ring chronology for more than nine millennia an initial assessment of long term e uctuations in yamal summer warmth has been realized through the reconstruction of tree line dynamics using a combination of dendrochron ological absolute dated material and less precisely radiocarbon dated older subfossils

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

climatic interpretation of the recently extended vostok ice records a new ice core drilled at the russian station of vostok in antarctica reached 2755 m depth in september 1993 at this depth the glaciological time scale provides an age of 260 ky bp 25 we refine this estimate using records of dust and deuterium in the ice and of 18o of o2 in the entrapped air 18o of o2 is highly correlated with insolation over the last two climatic cycles if one assumes that the egt chronology overestimates the increase of age with depth by 12 for ages older than 112 ky bp this modified age depth scale gives an age of 244 ky bp at 2755 m depth and agrees well with the age depth scale of walbroeck et al in press derived by orbital tuning of the vostok d record we discuss the temperature interpretation of this latter record accounting for the influence of the origin of the ice and using information derived from deuterium excess data we conclude that the warmest period of stage 7 was likely as warm as today in antarctica a remarkable feature of the vostok record is the high level of similarity of proxy temperature records for the last two climatic cycles stages 6 and 7 versus stages 1 5 this similarity has no equivalent in other paleorecords

glaciochemical investigation of an ice core from belukha glacier siberian altai 1 during summer 2001 a 140 m long ice core was recovered from the belukha glacier 49 48 26 n 86 34 43 e 4062 m a s l in the siberian altai the englacial temperature of 17 c indicates that this unique glaciochemical record is well preserved and suitable for the reconstruction of air pollution levels in this previously unexplored region the upper 86 m were dated by 210pb and cover the period 1862 2001 a lack of strong winter minima was observed in the 18o record and attributed to the small amount of precipitation during that season and to wind erosion the ion concentrations are comparable to those observed in swiss glaciers except for ammonium and formate where enhanced concentrations indicate biogenic emissions from siberian forests sulfate ammonium and nitrate records all show anthropogenic impacts despite the remoteness of this site

gas hydrate associated with mud diapirs in southern okinawa trough many mud diapirs have been recognized in southern okinawa trough by a multi channel seismic surveying on r v kexue i in 2001 gas hydrates have been identified by the seismic reflection characteristics the velocity analysis and the impedance inversion geothermal heat flow around the central of the mud diapir has been determined theoretically by the bottom simulating reflectors bsrs comparing the bsr derived and the measured heat flow values we infer that the bsr immediately at the top of the mud diapirs indicate the base of the saturated gas hydrate formation zone bsghfz but not as we ordinarily know the base of the gas hydrate stability zone bghsz which could be explained by the abnormal regional background heat flow and free gas flux associated with mud diapirs as a result it helps us to better understand the generation mechanism of the gas hydrates associated with mud diapirs and to predict the gas hydrate potential in the southern okinawa trough

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

climatic and atmospheric circulation pattern variability from ice core isotope geochemistry records altai tien shan and tibet several firn ice cores were recovered from the siberian altai belukha plateau central tien shan inilchek glacier and the tibetan plateau zuoqiupu glacier bomi from 1998 to 2003 the comparison analyses of stable isotope geochemistry records obtained from these firn ice cores identified the physical links controlling the climate related signals at the seasonal scale variability the core data related to physical stratigraphy meteorology and synoptic atmospheric dynamics were the basis for calibration validation and clustering of the relationships between the firn ice core isotope geochemistry and snow accumulation air temperature and precipitation origin the mean annual accumulation in water equivalent was 106 g cm 2 a 1 at inilchek glacier 69 g cm 2 a 1 at belukha and 196 gc m 2 a 1 at zuoqiupu the slopes in regression lines between the d 18 o ice core records and air temperature were found to be positive for the tien shan and altai glaciers and negative for southeastern tibet where heavy amounts of isotopically depleted precipitation occur during summer monsoons the technique of coupling synoptic climatology and meteorological data with d 18 o and d excess in firn core records was developed to determine climate related signals and to identify the origin of moisture in altai two thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation and the rest of the precipitation was recycled over aral caspian sources in the tien shan 87 of snow accumulation forms by precipitation originating from the aral caspian closed basin the eastern mediterranean and black seas and 13 from the north atlantic

environmental changes in the northern altai during the last millennium documented in lake teletskoye pollen record a high resolution pollen record from lake teletskoye documents the climate related vegetation history of the northern altai mountain region during the last millennium siberian pine taiga with scots pine fir spruce and birch dominated the vegetation between ca ad 1050 and 1100 the climate was similar to modern in the beginning of the 12th century birch and shrub alder increased lowered pollen concentrations and simultaneous peaks in herbs especially artemisia and poaceae ferns and charcoal fragments point to colder and more arid climate conditions than before with frequent fire events around ad 1200 regional climate became warmer and more humid than present as revealed by an increase of siberian pine and decreases of dry herb taxa and charcoal contents climatic conditions were rather stable until ca ad 1410 an increase of artemisia pollen may reflect slightly drier climate conditions between ad 1410 and 1560 increases in alnus betula artemisia and chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between ad 1560 and 1810 consistent with the little ice age after ad 1850 the vegetation gradually approached the modern one in conjunction with ongoing climate warming

the holocene younger dryas transition recorded at summit greenland analysis of ice from dye 3 greenland has demonstrated that the transition between the younger dryas and holocene climate periods occurred over a 40 year period a near annually resolved multiparameter record of the transition recorded in the gisp2 core from summit greenland shows that most of the transition occurred in a series of steps with durations of about 5 years some climate proxies associated with mid latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions changes in atmospheric water vapor are likely to have played a large role in the climate transition

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

dating of seasonal snow firn accumulation layers using pollen analysis reliable chronologies in ice cores and snow pits from many alpine glaciers in latitudes between 60 n and 60 s are often difficult to establish owing to problems with annual layer counting problems arise from melting wind erosion and the negligible amount of precipitation in some seasons all of which tend to obscure the seasonal variations in 18 o and chemical concentrations that are typically used to date ice cores however alpine glaciers contain many species of pollen grains that peak at particular times of the year we used the peaks in betulaceae pinus artemisia and a combination of abies and picea pollen species to determine the four seasonal layers of a snow pit on belukha glacier in russia s altai mountains comparing the pollen dated profiles with wind and precipitation records allows us to determine where a seasonal layer is missing thus the pollen dating method described here may be a useful tool to measure the annual snow deposition on alpine glaciers even when some seasonal layers are eroded by wind or missing due to negligible precipitation

ice cores from arctic sub polar glaciers chronology and post depositional processes deduced from radioactivity measurements the response of arctic ice masses to climate change is studied using ice cores containing information on past climatic and environmental features interpretation of this information requires accurate chronological data absolute dating of ice cores from sub polar arctic glaciers is possible using well known radioactive layers deposited by atmospheric nuclear tests maximum fallout in 1963 and the chernobyl accident 1986 analysis of several isotopes h 3 cs 137 shows that h 3 provides the most accurate dating of the 1963 maximum as indicated also in comparison with results from total beta measurements sr 90 and cs 137 mean annual net mass balances are derived from the dated ice cores from 1963 up to the date of the drillings the cs 137 and h 3 deposited by nuclear tests after decay correction are used to define a melt index for all 13 ice cores studied the relative strength of melting and percolation post depositional processes is studied on the basis of these cs 137 and h 3 deposits

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

a pronounced dry event recorded around 4 2 ka in brine sediments from the northern red sea partly laminated sediments were sampled from the brine filled anoxic shaban deep basin in the northern red sea at about 4200 cal yr bp more than two millennia of anoxic sedimentation is replaced by a sub oxic facies strongly suggesting the episodic absence of the brine at the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase within less than 100 yr pointing to a strong positive salinity anomaly at the sea surface this major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small shaban deep basin the timing and strength of the reconstructed environmental changes around 4200 cal yr bp suggest that this event is the regional expression of a major drought event which is widely observed in the neighboring regions and which strongly affected middle east agricultural civilizations

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

the evolution of dry lands in northern china and in the republic of mongolia since the last glacial maximum abstract the dry lands in china and mongolia include sand seas gravel deserts stable sand dunes desert steppe steppe and scrub woodlands environments distributed in a wide range of geomorphological and tectonic settings from 155 m below sea level to more than 5000 m asl in china the sandy deserts and gravel deserts are located in the arid regions mainly west of the helan mountains 106 e whereas the stable dune regions are distributed in the semi arid areas east of the helan mountains in mongolia deserts cover more than 40 of the country they are mainly distributed in the southern and southwestern part of the country in inter mountain valleys and basins of the altai mountains and in the uvs nuur basin in northwestern mongolia the desert regions enclose mainly gravel desert gobi and comprise some areas with sand fields and dune fields especially in western mongolia relict frost wedges and moraines in the chaidamu and tarim basins of china indicate that the coldest time of the last glaciation occurred at 30 25 ka in these two areas the stratigraphy of the dunes in the badain jaran desert high lake levels in the areas near and within the large deserts in china and in mongolia suggest a much more humid climate in western china and in mongolia during marine isotope stage three however the period after 24 ka to the end of the pleistocene was mostly characterised by increased temperature and reduced precipitation in the chaidamu and tarim basins paleoenvironmental conditions in the eastern part of the chinese desert belt were marked by an extensive widening of dune formation at 21 13 ka reflecting a weaker intensity of east asian summer monsoon during the holocene higher lake levels stratigraphy of dunes and results of palynological isotopical and sedimentological analyses of lacustrine sediments in the western china and mongolia suggest a few wetter periods especially in the earlier part of the holocene the holocene climatic conditions in the eastern part of the chinese deserts have enabled stabilisation of dunes and formation of soils the presently active dunes in this region are a result of desertification due to human influences recent investigations in the dry lands of china and mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates

rhythmic fine grained sediment deposition in lake teletskoye altai siberia in relation to regional climate change abstract the climatic evolution of the altai mountains southern siberia has been reconstructed for the last eight centuries from high resolution analysis of the sediment of lake teletskoye 137 cs and 14 c age estimates indicate a mean sedimentation rate of about 1 mm year with each analyzed sample corresponding to 1 5 year intervals from sediment analysis and statistical treatments a model is proposed for a correlation between changes in the sedimentary facies during the past 160 years and climatic parameters based on meteorological records available for this period by further extending this calibration of sedimentary proxy responses over the estimated past 800 years several distinct intervals indicative of regional climate change are found in lake teletskoye records for instance from 1210 to 1480 the climate appears to have been warmer and more humid than today between 1480 and 1580 regional climate became more cool and arid over the interval from 1580 to 1840 climate conditions were cool and arid whereas after 1840 annual average temperatures seem to have increased lithologic responses suggest that several short impulses of drought in the region might have taken place during the past 800 years