glacial stage ice core records from the subtropical dunde ice cap china the first ice core record of both the holocene and wisconsin wiirm late glacial stage lgs from the subtropics has been extracted from three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau ice thicknesses at the ice cap summit average 138 m the bedrock surface is relatively flat surface and basal temperatures are 7 3 and 4 7 c respectively and the ice cap exhibits radial flow away from the summit dome these records reveal a major change in the climate of the plateau 10 000 years ago and suggest that lgs conditions were colder wetter and dustier than holocene conditions this is inferred from the more negative 6180 ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes which characterize the lgs part of the cores total b radioactivity from shallow ice cores indicates that over the last 24 years the average accumulation rate has been 400 mm a 1 at the summit the ice cores have been dated using a combination of annual layers in the insoluble dust and 6180 in the upper sections of core visible dust layers which are annual and ice flow modeling the oxygen isotope record which serves as a temperature proxy indicates that the last 60 years have been the warmest in the entire record

himalayan ice core dating with snow algae snow algae in shallow ice cores 7 m long from yala glacier in the lang tang region of nepal were examined for potential use in ice core dating ice core samples taken at 5350 m a s l in 1994 contained more than seven species of snow algae in a vertical profile of the algal biomass 11 distinct algal layers were observed seasonal observation in 1996 at the coring site indicated most algal growth occurred from late spring to late summer pit observation in 1991 1992 and 1994 indicated that algal layer formation takes place annually 18 o chemical ions na cl so 4 2 and no 3 and microparticles failed to show any clear seasonal variation particularly at depths exceeding 2 m possibly due to heavy meltwater percolation snow algae in ice cores would thus appear to be accurate boundary markers of annual layers and should prove useful for ice core dating in himalayan type glaciers

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

glacier mass balance interpreted from biological analysis of firn cores in the chilean lake district the first analyses of biological components in glaciers of the chilean lake district are presented based on microalgae biovolume pollen and other microorganisms detected in shallow 10 m firn ice cores three cores were retrieved two at volcan mocho choshuenco 39855 0 s 72802 0 w summit at 2422 m a s l east glacier at 2000 m a s l and one at the summit of volcan osorno 41806 0 s 72830 0 w 2652 m a s l microalgae protozoa and pollen quantified in the samples obtained from the two summit cores show clear fluctuations interpreted as seasonal signs in contrast dd and many chemical species from the summit cores show strong dampening at depth probably due to water percolation the limited information provided by isotopic and chemical analyses is used to support the seasonal interpretation of biological parameters from the summit cores with microorganism maxima inferred to occur in summer and pollen maxima in spring a good comparison is found between mass balance estimations from the volcan mocho choshuenco summit core and values obtained near that site by means of the stake method it is concluded that biological analyses of firn ice cores provide reliable estimations of annual and seasonal markers from these temperate glaciers

10 be in ice at vostok antarctica during the last climatic cycle we have previously reported accelerator mass spectrometer measurements of the cosmogenic isotope 10be half life 1 5 myr in an 906 m ice core recovered at dome c antarctica1 in addition to an enhanced concentration during a period of reduced solar activity maunder minimum ad 1645 1715 2 we found substantially increased concentrations during that part of the core corresponding to the last ice age both effects have been confirmed and extended in greenland ice cores3 4 the recovery of a 2 083 m ice core at vostok antarctica5 together with an extended oxygen isotope chronology reported elsewhere in this issue6 permits an extension of 10be studies over the whole of the last climatic cycle 125 kyr we report here such measurements which show an excellent correlation with the oxygen isotope and thus presumably climate record over the whole of this period the results imply that precipitation rates in the antarctic during the last interglacial were similar to those of the holocene but were roughly halved during the last glaciation

latest pleistocene and holocene glacier fluctuations in the himalaya and tibet abstract the timing and extent of latest pleistocene and holocene alpine glacier fluctuations in the himalaya and tibet are poorly defined due to the logistical and political inaccessibility of the region and the general lack of modern studies of the glacial successions nevertheless renewed interest in the region and the aid of newly developing numerical dating techniques have provided new insights into the nature of latest pleistocene and holocene glacier oscillations these studies provide abundant evidence for significant glacial advances throughout the last glacial cycle in most high himalayan and tibetan regions glaciers reached their maximum extent early in the last glacial cycle however true last glacial maximum glacier advances were significantly less extensive notable glacier advances occurred during the lateglacial and the early holocene with minor advances in some regions during the mid holocene there is abundant evidence for multiple glacial advances throughout the latter part of the holocene although these are generally very poorly defined and were less extensive than the early holocene glacier advances the poor chronological control on latest pleistocene and holocene glacial successions makes it difficult to construct correlations across the region and with other glaciated regions in the world which in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation in this region the lateglacial and holocene glacial record however is particularly well preserved in several regions notably in muztag ata and kongur and the khumbu himal these successions have the potential to be examined in detail using newly developing numerical dating methods to derive a high resolution record of glaciation to help in paleoclimatic reconstruction and understanding the dynamics of climate and glaciation in the himalaya and tibet

holocene paleoclimatology of the queen elizabeth islands canadian high arctic abstract a wide variety of evidence reflecting in different ways the changing climate of the queen elizabeth islands during the holocene is reviewed all proxies pertain to summer conditions many sources of information provide weak or equivocal paleoclimatic signals but a general pattern of events can be discerned temperatures in the early to mid holocene were highest comparable with or higher than temperatures prevailing for much of this century although much evidence points to a mid holocene thermal maximum there is also considerable evidence that conditions were warmer in the early holocene possibly related to orbitally induced radiation anomalies the apparent mid holocene thermal maximum may reflect lags in the response of the environment and of some proxies in recording paleoclimatic conditions more direct indices point to warmest conditions in the early holocene before 7500 bp temperatures declined from 3000 bp culminating in exceptionally low temperatures from 100 400 bp this may have been the coldest period of the entire holocene resulting in glacier advances to post glacial maximum positions the period since 1925 has witnessed a pronounced increase in temperature leading to negative mass balances on glaciers and ice sheets throughout the archipelago this period is the warmest for at least 1000 years and perhaps for several thousand years modern climate in the queen elizabeth islands may thus be characteristic of the early to mid holocene and atypical of conditions which prevailed for much of the last few thousand years

a pollen record of holocene climatic changes from the dunde ice cap qinghai tibetan plateau pollen preserved in ice cores from the dunde ice cap provides a sensitive record of holocene climatic changes and vegetational response in the northern qinghai tibetan plateau at time scales ranging from millennia to centuries and decades pollen analysis of the annually resolvable ice layers for a 30 yr period 1957 1986 suggests that total pollen concentration is correlated positively with summer precipitation and negatively with summer temperature thus it is a sensitive indicator of moisture availability and vegetation density in the steppe and desert regions around dunde high pollen concentrations between 10 000 and 4800 yr b p suggest that the summer monsoon probably extended beyond its present limit to reach dunde and westernmost tibet in response to orbital forcing the summer monsoon retreated time transgressively across the qinghai tibetan plateau during the middle holocene relatively humid periods occurred at 2700 2200 1500 800 and 600 80 yr b p probably as a result of neoglacial cooling prominent pollen changes during the medieval warm period 790 620 yr b p and the little ice age 330 80 yr b p suggest that the vegetation in the qinghai tibetan plateau region is sensitive to abrupt century scale climatic changes such as those anticipated in scenarios of greenhouse warming

ice core pollen record of climatic changes in the central andes during the last 400 yr abstract this paper presents a high resolution ice core pollen record from the sajama ice cap bolivia that spans the last 400 yr the pollen record corroborates the oxygen isotopic and ice accumulation records from the quelccaya ice cap and supports the scenario that the little ice age lia consisted of two distinct phases a wet period from ad 1500 to 1700 and a dry period from ad 1700 to 1880 during the dry period xerophytic shrubs expanded to replace puna grasses on the altiplano as suggested by a dramatic drop in the poaceae asteraceae p a pollen ratio the environment around sajama was probably similar to the desert like shrublands of the southern bolivian highlands and western andean slopes today the striking similarity between the sajama and quelccaya proxy records suggests that climatic changes during the little ice age occurred synchronously across the altiplano

a quantitative comparison of microfossil extraction methods from ice cores microfossil records from ice archives allow vegetation fire and land use activity reconstructions on broad spatial scales samples typically contain low microfossil concentrations therefore large ice volumes are often needed for palynology hence it is crucial to extract maximum microfossil numbers through appropriate physical chemical treatments we compare six methods covering the main water reduction procedures evaporation filtration and centrifugation with snow samples adding a known number of lycopodium marker spores prior to sample treatment and a second marker eucalyptus after laboratory processing allows a quantitative microfossil loss assessment during pollen extraction we applied the best performing method average loss of 22 to high alpine firn cores from colle gnifetti glacier for validation with a natural archive containing extremely low microfossil concentrations we conclude that samples processed with different microfossil extraction protocols may give different results for pollen concentrations percentages and ratios between different pollen types especially if vesiculate conifer pollen is an important pollen assemblage component we recommend a new evaporation based method which delivers the smallest and least variable losses among the tested approaches since microfossil losses are inevitable during laboratory procedure adding markers prior to sample processing is mandatory to achieve reliable microfossil concentration and influx estimates

elevated paleomagnetic dispersion at saint helena suggests long lived anomalous behavior in the south atlantic earth s magnetic field is presently characterized by a large and growing anomaly in the south atlantic ocean the question of whether this region of earth s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics core mantle interaction and the possibility of an imminent magnetic polarity reversal here we present paleomagnetic data from saint helena a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the south atlantic on timescales of millions of years our results supported by positive baked contact and reversal tests produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago but with very large associated directional dispersion these findings indicate that on geological timescales geomagnetic secular variation is persistently enhanced in the vicinity of saint helena this in turn supports the south atlantic as a locus of unusual geomagnetic behavior arising from core mantle interaction while also appearing to reduce the likelihood that the present day regional anomaly is a precursor to a global polarity reversal

the potential effects of percolating snowmelt on palynological records from firn and glacier ice the effects of meltwater percolation on pollen in snow firn and glacial ice are not fully understood and currently hamper the use of pollen in ice core studies of paleoclimate several studies have suggested that due to grain size pollen is not mobilized by meltwater transport however these findings contradict many ice core pollen studies that show pollen concentrations in snow and firn are much higher than concentrations found in the ice layers they eventually form this study addresses one aspect of this question by investigating whether meltwater percolation can effectively transport pollen within a snowpack we used nine styrofoam coolers filled by natural snow accumulation the coolers were tested in three groups of three replicates each to simulate different glacier snowpack conditions and spiked at the surface with a known amount of lycopodium marker spores the snow was melted to two thirds the original volume sampled stratigraphically and tested for spore concentrations meltwater effluent was also collected and examined results show substantial vertical and horizontal spore transport during the experiment peak spore concentrations were found in the bottommost snow layer or in the meltwater effluent in eight of nine coolers indicating that the majority of surface spores were transported through the snowpack via meltwater percolation and or runoff

comments on brugger and others 2018 a quantitative comparison of microfossil extraction methods from ice cores in our comments we re evaluate brugger and others 2018 lycopodium eucalyptus double marker approach based on the fact that previous evidence already demonstrated that the batch of eucalyptus tablets used by brugger and others 2018 is not suitable for quantitative comparisons as they are characterized by inconsistent pollen concentration we present clear evidence that the eucalyptus tablets do feature inaccurate pollen concentrations and are therefore improper for all quantitative comparisons of microfossil extraction methods consequently the results of the quantitative and qualitative assessment of different pollen extraction methods from ice samples compiled by brugger and others 2018 are highly questionable due to the use of faulty marker tablets

absolute reconstruction of the closing of the mongol okhotsk ocean in the mesozoic elucidates the genesis of the slab geometry underneath eurasia understanding the present day fast seismic velocity anomalies in the mantle requires an accurate kinematic reconstruction of past convergent tectonics using the paleomagnetism based absolute reconstruction method from wu and kravchinsky 2014 we present here the restoration of the closing of the mongol okhotsk ocean moo that existed between siberia and north china amuria nca during the mesozoic three stages i e 250 200 ma 200 150 ma and 150 120 ma are identified from the time varying convergence rates of siberia and nca the spherical distance between the suture margins was reduced by ca 66 7 at an average convergence rate of 8 8 0 6 cm yr during the first stage at 250 200 ma when ca 62 5 76 1 of the slabs associated with the moo lithosphere were formed primarily through intra oceanic convergence in the second stage at 200 150 ma the spherical distance was reduced by another 21 1 with a convergence rate of 3 6 0 3 cm yr during this stage ca 14 2 30 9 of the moo slabs were formed and continental oceanic convergence outpaced intra oceanic subduction in the last stage at 150 120 ma the convergence rate dropped to ca 0 4 0 6 cm yr with the formation of ca 4 6 9 8 slabs associated with the moo lithosphere the final closure of the moo remnant basin could have been accomplished by 130 120 ma which explains the origin of the fast velocity anomalies inside the restored continents at 120 ma near the suture margins

bayesian inversion for the filtered flow at the earth s core mantle boundary the inverse problem of determining the flow at the earth s core mantle boundary according to an outer core magnetic field and secular variation model has been investigated through a bayesian formalism to circumvent the issue arising from the truncated nature of the available fields we combined two modeling methods in the first step we applied a filter on the magnetic field to isolate its large scales by reducing the energy contained in its small scales we then derived the dynamical equation referred as filtered frozen flux equation describing the spatiotemporal evolution of the filtered part of the field in the second step we proposed a statistical parametrization of the filtered magnetic field in order to account for both its remaining unresolved scales and its large scale uncertainties these two modeling techniques were then included in the bayesian formulation of the inverse problem to explore the complex posterior distribution of the velocity field resulting from this development we numerically implemented an algorithm based on markov chain monte carlo methods after evaluating our approach on synthetic data and comparing it to previously introduced methods we applied it to a magnetic field model derived from satellite data for the single epoch 2005 0 we could confirm the existence of specific features already observed in previous studies in particular we retrieved the planetary scale eccentric gyre characteristic of flow evaluated under the compressible quasi geostrophy assumption although this hypothesis was not considered in our study in addition through the sampling of the velocity field posterior distribution we could evaluate the reliability at any spatial location and at any scale of the flow we calculated the flow uncertainties we determined are nevertheless conditioned by the choice of the prior constraints we applied to the velocity field

ice age initiation by an ocean atmospheric circulation change in the labrador sea abstract the contrast between the large greenland ice sheet and the nearly ice free area of canada to the west exemplifies the critical role of the moisture supply in glaciation the trigger for new ice sheet growth in canada at the end of the last interglacial was probably an increase in the moisture supply rather than regional cooling triggering is attributed to stronger storm activity in the labrador baffin area caused by warming in the labrador sea and cooling in the greenland norwegian sea the key to this temperature and circulation change may have been an increase in the hydrologic deficit of the mediterranean sea a larger hydrologic deficit would have increased mediterranean salinity and consequently the volume of mediterranean overflow water a resulting increased upwelling of mediterranean overflow water from the lower thermocline off scotland would have diverted additional warm north atlantic drift water westward via the irminger current thus warming the labrador sea the underlying cause of the hydrologic deficit increase was diminishing milankovitch summer insolation in lower latitudes this reduced african monsoon intensity and nile river discharge in modern times nearly all nile discharge to the mediterranean has been lost due to irrigation practices culminating with the completion of the aswan high dam in 1968 the total increase in the hydrologic deficit due to nile discharge loss is now 8 in the next 70 100 years the nile loss added to larger evaporative losses due to co 2 warming may increase the deficit as much as 22 above the inferred deficit at the beginning of the last glaciation thus further warming the labrador sea consequently the triggering of major ice sheet growth in canada 100 years from now is possible

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

environmental change during the holocene in western china on a millennial timescale recent data on the evolution of the inland lakes loess palaeosol sequences and glacier variations in western china are briefly reviewed the lake history shows three distinct stages in the holocene i e low water levels before 7500 bp a stage of expansion during the climatic optimum between 7500 and 3500 bp and contraction after 3500 bp three stages wooded grassland mixed woodland wooded grassland becoming steppe also appear indicated by the holocene loess palaeosol sequence in the lanzhou region the optimal period for soil development being between 7500 and 3500 bp there were seven periods of glacier advance the continental glaciers advanced at about 8300 5700 4000 and 400 bp in northwestern china and the maritime glaciers advanced at about 3000 2000 1000 and 200 bp it is suggested that the climatic changes show two periodicities during the holocene namely at intervals of about 2500 and 1000 years

use of ice cores from glaciers with melting for reconstructing mean summer temperature variations this study examines a new method for reconstructing mean summer temperature variations by using an ice core from a wet snow zone on a summer accumulation type glacier in july 2001 a 25 1 m deep ice core was recovered from the accumulation area of sofiyskiy glacier 49847 0 n 87843 0 e 3435 m a s l located in the southern chuyskiy range of the russian altai mountains and a 4 5 m deep pit was excavated about 50 m northwest of the drill site the observation site has a positive balance even during summer when melting occurs the summer balance for each year from 1990 to 2000 was estimated from pinaceae and artemisia pollen peaks in these samples pinaceae pollen marks spring whereas artemisia pollen marks autumn moreover meltwater intrusion did not reach the previous year s accumulation thus the ice between these pollen peaks in the same year was used to estimate a summer balance the reconstructed summer balance variations were negatively correlated with mean summer temperature variations r 0 72 p 0 05 this study shows that for summer accumulation type glaciers such as sofiyskiy glacier the most important climate factor controlling the glacier s surface mass balance is mean summer temperature therefore the summer layer thickness in an ice core can be used as a proxy for reconstructing mean summer temperature variations

summer temperature reconstruction on the central tibetan plateau during 1860 2002 derived from annually resolved ice core pollen 1 we present a 140 year ice core pollen record with annual time resolution from the puruogangri ice field in the central tibetan plateau a linear regression model between the sum of the steppe and meadow pollen taxa and summer temperature at naqu accounts for 66 of the summer temperature variance for the period 1955 2002 on the basis of this model we reconstructed summer temperature history for the central tibetan plateau from 1860 to 2002 three marked warm periods during the 1870s 1890s and 1990s and five cold periods during the 1860s 1880s 1900s 1950s and 1960 1970s were identified within the last 100 years late 20th century warming is distinctive and may have had a major role in the present retreat of most glaciers on the tibetan plateau the pollen record is also significantly correlated with average annual temperatures over the whole tibetan plateau suggesting that these proxy data have the potential for reflecting large scale regional temperature change the statistically significant similarity between the puruogangri ice core pollen record and the 18o time series indicates that both are reliable indicators of temperature change at annual to multiyear timescales in this region

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

glaciochemical dating of an ice core from upper grenzgletscher 4200 m a s l one crucial condition for the interpretation of ice core records is the establishment of an accurate time scale this task is especially difficult for glacier sites in a complex topography such as the alps due to the often irregular deposition of fresh precipitation in this work dating techniques were applied to an alpine ice core from upper grenzgletscher monte rosa massif 4200 m a s l representing about two thirds of the total glacier thickness they are based on i the radioactive decay of the isotope 210 pb ii seasonally varying signals such as the concentrations of nh 4 and the isotopic ratio 18 o and iii stratigraphic markers from saharan dust falls atmospheric nuclear weapon tests and the reactor accident in chernobyl from the combined application of these dating methods a time period of 1937 94 covered by the ice core was derived dating uncertainty is 1 year for the period 1970 94 and 2 years for the period 1937 69 the observed thinning of the annual layers as a function of depth could be well described by a simple kinematic glacier flow model

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

discussion of the paper switch of ne asia from extension to contraction at the mid cretaceous a tale of the okhotsk oceanic plateau from initiation by the perm anomaly to extrusion in the mongol okhotsk ocean by kai jun zhang li long yan chen ji

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

cretaceous accretionary complex related to okhotsk chukotka subduction omgon range western kamchatka russian far east abstract the omgon range of western kamchatka contains a mid to upper cretaceous sequence of flysch with tectonic inclusions of jurassic cretaceous oceanic rocks inferred to have been imbricated together in an accretionary prism these rocks were tectonically juxtaposed during the cretaceous in a melange that contains a number of elements but mainly includes 1 middle jurassic lower cretaceous volcanic rocks formed in an oceanic and or marginal sea environment and 2 albian campanian terrigenous turbidites made of quartz rich clastic sediments that accumulated near a continental margin the oceanic rocks are inferred to have been tectonically incorporated into the continental terrigenous unit by offscraping during subduction the accretionary prism resulted from subduction of the pacific paleo oceanic plate izanagi under the eurasian continental margin which ultimately caused volcanism in the inboard okhotsk chukotka volcanic belt internal imbrication was completed by the maastrichtian 70 ma as indicated by apatite fission track ages that record cooling and exhumation of this crustal block the omgon accretionary wedge originated in a similar geodynamic setting and same time as the yanranai northern korayk tonino aniva southeastern sakhalin hidaka northeastern japan and cretaceous part of the shimanto belt southwestern japan the similarities of ages lithology and tectonic setting suggest that the omgon accretionary wedge was part of a paleo subduction zone along the eurasian margin during the mid to late cretaceous

dating of two nearby ice cores from the illimani bolivia 1 in order to establish a chronology of two nearby ice cores from a glacier at illimani 6438 m bolivia a broad dating approach is presented here which in particular makes use of the fast simple and nearly nondestructive electrical conductivity method ecm that provides a highly resolved record thus ecm is suited for counting annual layers in the ice especially for ice cores extracted from high mountain glaciers with a fast layer thinning furthermore ecm can be used for detecting volcanic signals annual signals in the ecm record of the illimani ice core were identified using the 1964 a d tritium reference horizon and were counted along 125 m or 90 of the core representing the time period from 1200 240 a d estimated accumulated error to 1999 a d the resulting age depth relationship was supported by counting annual peaks in the microparticle record as well as by nuclear dating using the decay of 210pb the identification of volcanic signals originating from eruptions such as pinatubo 1991 a d el chichon 1982 a d agung 1963 a d krakatoa 1883 a d tambora 1815 a d and the unknown 1258 a d significantly reduced the uncertainty of annual layer counting alc to 2 years in the vicinity of these events

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

pollen from accurately dated speleothems supports alpine glacier low stands during the early holocene deciphering pollen assemblages from alpine speleothems holds potential to provide unique information about past vegetation in rapidly changing environments here we reconstruct subsurface aerosol transport at milchbach cave switzerland 1840 m asl based on the pollen content of two holocene stalagmites we demonstrate that pollen is chiefly associated with bacterially mediated calcite fabrics typical of a well ventilated cave system in contrast pollen is absent from columnar calcite fabrics confirming that hydrological transport is not a significant process for the incorporation of pollen into speleothems at milchbach cave our results support significant changes in the subsurface ventilation regime which can be associated with the waxing and waning of upper grindelwald glacier pollen assemblages obtained from six carbonate sub samples attest the presence of a mixed deciduous forest in the grindelwald valley during the early and middle holocene in agreement with coeval regional pollen records this study demonstrates that even small amounts of calcite 0 3 2 8 cm3 are capable of delivering pollen spectra representative of the original vegetation if sufficiently elevated deposition fluxes are provided

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

ammonium concentration in ice cores a new proxy for regional temperature reconstruction 1 we present a reconstruction of tropical south american temperature anomalies over the last 1600 years the reconstruction is based on a highly resolved and carefully dated ammonium record from an ice core that was drilled in 1999 on nevado illimani in the eastern bolivian andes concerning the relevant processes governing the observed correlation between ammonium concentrations and temperature anomalies we discuss anthropogenic emissions biomass burning and precipitation changes but clearly favor a temperature dependent source strength of the vegetation in the amazon basin that given the reconstruction reveals that medieval warm period and little ice age type episodes are distinguishable in tropical south america a region for which until now only very limited temperature proxy data have been available for the time period from about 1050 to 1300 ad our reconstruction shows relatively warm conditions that are followed by cooler conditions from the 15th to the 18th century when temperatures dropped by up to 0 6 c below the 1961 1990 average the last decades of the past millennium are characterized again by warm temperatures that seem to be unprecedented in the context of the last 1600 years

a holocene ice core pollen record from ellesmere island nunavut canada abstract a holocene record of pollen deposition was obtained from an ice core drilled through the agassiz ice cap the pollen records long range atmospheric transport to the ice cap pollen concentrations were highest in the early holocene 15 grains l decreased in the mid holocene 6 grains l and increased in the late holocene 9 grains l in the early holocene the higher concentration of tree pollen at a time when large parts of canada were still ice covered and when forest was generally farther away implies that atmospheric circulation was stronger than at present following deglaciation as vegetation migrated north in central and eastern canada sources of pollen were closer to the agassiz ice cap however the concentration of tree pollen decreased on the ice cap this was followed by several relatively rapid changes after 3500 yr ago until ca 3500 yr ago the pollen concentration curves resembled the ice core 18 o and summer melt layer curves both regarded as temperature proxies

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

palaeomagnetism of the west sakhalin basin evidence for northward displacement during the cretaceous summary a significant margin parallel translation of terranes is postulated by all models for tectonic evolution of the east asian continental margin although the timing and magnitude of displacements of individual elements are poorly constrained as yet the west sakhalin basin a forearc basin associated with the cretaceous volcanic arcs is one of the displaced tectonic elements our palaeomagnetic study of the basin rocks provides the first quantitative constraints on its cretaceous history we identified a characteristic magnetization in the berriasian valanginian basalt representing the oceanic basement of the basin and four characteristic magnetizations in a continuous sequence of the albian to maastrichtian siliciclastic fill of the basin a combination of the positive fold conglomerate and reversals tests supports the primary origin of the remanence in the sediments palaeomagnetic data indicate a gradual shift of the west sakhalin basin from subequatorial latitudes during the early cretaceous to about 40on by the late cretaceous the main phase of the margin parallel migration took place during the early cretaceous and ended by the cenomanian the continuous sedimentary sequence records 50 degrees of progressive clockwise rotation during the late cretaceous

discussion on switch of ne asia from extension to contraction at the mid cretaceous a tale of the okhotsk oceanic plateau from initiation by the perm anomaly to extrusion in the mongol okhotsk ocean reply abstract we disagree the comment by zyabrev and abrajevitch 2020 because neither the data nor the ideas they presented are new we stress that the diachronous closure of the mongol okhotsk ocean should be highlighted that the existence and timing of the early cretaceous okhotsk oceanic plateau are sound that the motion of the okhotsk oceanic plateau towards the pacific subduction zone is reasonable and that an island arc bound by a paleo pacific subduction zone since 140 ma is highly probable

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

biological ice core analysis of sofiyskiy glacier in the russian altai we examined microorganisms and pollen in a pit 4 5m deep and a shallow ice core 25 01m long from sofiyskiy glacier in the altai mountains of russia for potential use in dating ice cores from a mid latitude glacier the ice core and pit samples contained various green algae cyanobacteria bacteria fungi and pollen in the vertical profiles of the pit algal biomass peaks corresponded to high 18o layers and pinaceae pollen peaks suggesting that these algae grew during the melt season in contrast the layer with the lowest 18o contained almost no algal cells major peaks of the cyanobacteria bacteria and a fungus roughly corresponded to those of the algae however seasonal changes in these microorganisms became indistinct deeper in the core as did the seasonal variation in 18o and major ions most likely due to heavy meltwater percolation and or post depositional decomposition in contrast clear seasonal cycles were evident in the algal biomass and pollen in snow samples assuming that the peaks of the snow algae and pinaceae pollen marked summer layers and that the layers with almost no snow algae represented the winter layers we estimated that the ice core contained 16 annual layers 1985 2001 the mean annual mass balance for the period was estimated to be 1 01mw e the value agreed well with those estimated from stake measurements indicating that snow algae and pollen could provide reliable boundary markers of annual layers in the ice cores of this region

why loss matters reply to the comments of festi and others on a quantitative comparison of microfossil extraction methods from ice cores by brugger and others 2018

tectonostratigraphic evolution of the mohe upper amur basin reflects the final closure of the mongol okhotsk ocean in the latest jurassic earliest cretaceous abstract the mohe upper amur basin to the south of the eastern mongol okhotsk suture zone contains important stratigraphic records for understanding the closure of the eastern mongol okhotsk ocean the basin is crossed by the russia china border and its chinese and russian parts are known as the mohe basin and upper amur basin respectively using most up to date data on stratigraphy sedimentology petrography and detrital zircon u pb geochronology this study establishes the stratigraphic correlation between the two mohe and upper amur parts of the basin and analyzes depositional ages provenance and paleogeography of their jurassic lower cretaceous strata the adopted middle late jurassic ages for the xiufeng ershierzhan emuerhe and kaikukang formations in the mohe basin are revised and constrained to late kimmeridgian tithonian berriasian early valanginian and late valanginian ages respectively during the late kimmeridgian tithonian extension occurred in the mohe upper amur basin and sediments were mainly sourced from areas to the south of the basin later in the berriasian early valanginian the northern margin of the mohe upper amur basin was uplifted and started furnishing sediments into the basin in the late valanginian regional uplift of the northern part of the mohe upper amur basin transformed the basin into a compressional intermountain basin with sedimentation localized in its southern part after the valanginian extension and associated volcanism occurred in the basin we suggest that the evolution of the mohe upper amur basin reflects the gradual closure of the eastern mongol okhotsk ocean and associated collision of the siberia craton and the amuria block that occurred from the kimmeridgian tithonian to the west of the basin through to the berriasian valanginian to the north and northeast of the basin the final closure of the mongol okhotsk ocean to the north of the mohe upper amur basin in the earliest cretaceous significantly affected the sedimentological structural and tectonic evolution of northeast asia

the onset of neoglaciation 6000 years ago in western mongolia revealed by an ice core from the tsambagarav mountain range glacier highstands since the last glacial maximum are well documented for many regions but little is known about glacier fluctuations and lowstands during the holocene this is because the traces of minimum extents are difficult to identify and at many places are still ice covered limiting the access to sample material here we report a new approach to assess minimal glacier extent using a 72 m long surface to bedrock ice core drilled on khukh nuru uul a glacier in the tsambagarav mountain range of the mongolian altai 4130 m asl 48 39 338 n 90 50 826 e the small ice cap has low ice temperatures and flat bedrock topography at the drill site this indicates minimal lateral glacier flow and thereby preserved climate signals the upper two thirds of the ice core contain 200 years of climate information with annual resolution whereas the lower third is subject to strong thinning of the annual layers with a basal ice age of approximately 6000 years before present bp we interpret the basal ice age as indicative of ice free conditions in the tsambagarav mountain range at 4100 m asl prior to 6000 years bp this age marks the onset of the neoglaciation and the end of the holocene climate optimum the ice free conditions allow for adjusting the equilibrium line altitude ela and derive the glacier extent in the mongolian altai during the holocene climate optimum based on the ela shift we conclude that most of the glaciers are not remnants of the last glacial maximum but were formed during the second part of the holocene the ice core derived accumulation reconstruction suggests important changes in the precipitation pattern over the last 6000 years during formation of the glacier more humid conditions than presently prevailed followed by a long dry period from 5000 years bp until 250 years ago present conditions are more humid than during the past millennia this is consistent with precipitation evolution derived from lake sediment studies in the altai

on core surface flows inferred from satellite magnetic data abstract satellite data allows the magnetic field produced by the dynamo within the earth s core to be imaged with much more accuracy than previously possible with only ground based data changes in this magnetic field can in turn be used to make some inferences about the core surface flow responsible for them in this paper we investigate the improvement brought to core flow computation by new satellite data based core magnetic field models it is shown that the main limitation now encountered is no longer the now high accuracy of those models but the non modelled secular variation produced by interaction of the non resolvable small scales of the core flow with the core field and by interaction of the partly resolvable large scales of the core flow with the small scales of the core field unfortunately masked by the crustal field we show how this non modelled secular variation can be taken into account to recover the largest scales of the core flow in a consistent way we also investigate the uncertainties this introduces in core flows computed with the help of the frozen flux and tangentially geostrophic assumptions it turns out that flows with much more medium and small scales than previously thought are needed to explain the satellite data based core magnetic field models it also turns out that a significant fraction of this flow unfortunately happens to be non recoverable being either non resolvable because too small scale or invisible because in the kernel of the inverse method even though it produces the detectable non modelled secular variation applying this to the magsat 1980 to orsted 2000 field changes leads us to conclude that a flow involving at least strong retrograde vortices below the atlantic hemisphere some less resolved prograde vortices below the pacific hemisphere and some poorly resolved and partly non resolvable polar vortices is needed to explain the 1980 2000 satellite era average secular variation the characteristics of the fraction of the secular variation left unexplained by this flow are also discussed

application of pollen analysis to dating of ice cores from lower latitude glaciers 1 ice cores from temperate regions have long been expected to be useful for understanding local climate trends but a reliable dating method has proved difficult here we show that measurements of pollen using samples with only 10 ml of water can give an accurate measure of the annual ice accumulation in addition two major types of pollen allow us to estimate the summer ice accumulation as well as the annual accumulation

a modern pollen spectrum from dye 3 south greenland ice sheet results of pollen analysis of a large firn sample from dye 3 southern greenland are reported the sample was divided into three sections all dominated by pine birch and ragweed pollen pollen concentration for the entire sample is 15 pollen grains per litre and the annual pollen deposition rate has been estimated at approximately 0 73 grains cm 2 year 1 7300 grains m 2 a 1 although these values are slightly lower than expected considering the relatively southern latitude of the site they are within the range of values obtained from other arctic ice caps

assessing source areas of pollutants from studies of fly ash charcoal and pollen from svalbard snow and ice 1 temporal variations in the quantities of pollen charcoal and scp spheroidal carbonaceous particles contained in the lomonosovfonna ice core from svalbard and in the surface snow of the ice cap are presented the abundance of these microparticles is illustrated for the period a d 1850 1997 from the ice core together with detailed snow pit stratigraphies for summer 2001 to spring 2002 viewing scp and pollen together is a new approach with relevance for tracing the possible origin of contaminants the scp are related to the pollution source while the pollen gives an indication of the vegetation at the point of origin the deposition of scp on the ice is also compared with deposition of scp in northern fennoscandia for the period a d 1982 1997 the quantity of pollen and the pollen types recorded suggest an origin in fennoscandia rather than in north america the temporal pattern of both scp and charcoal deposition reflects that of europe but may also contains a local signal

a short lived but significant mongol okhotsk collisional orogeny in latest jurassic earliest cretaceous abstract the central asian orogenic belt caob is one of the largest orogenic collages on earth which records a long history of accretionary orogenesis from the late proterozoic to the mesozoic although paleomagnetic studies have unanimously suggested that the major mongol okhotsk ocean in the eastern caob closed mainly during the late jurassic early cretaceous few conclusive and self consistent geological studies in central asia and east asia have confirmed the occurrence of this significant collisional orogeny based mainly on basin evolution in the caob tarim block north china block and qaidam qialian block during the late jurassic early cretaceous the present study proposes that a short lived but significant mongol okhotsk collisional event occurred in the latest jurassic earliest cretaceous the rapid closure of the mongol okhotsk ocean was possibly related to the clockwise rotation of siberia which was driven by the continental collision between the siberia craton and the kolyma omolon microcontinent in northeast russia in the late jurassic owing to the clockwise rotation of siberia and the subsequent closure of the mongol okhotsk ocean a number of areas to both the east and the west of the mongol okhotsk suture underwent uplift and erosion including lake baikal transbaikalia sayan ranges altai shan junggar basin turfan basin tarim basin tian shan mohe basin great xing an ranges hailar tamsag basin erlian basin songliao basin east gobi basin yingen basin bei shan yin shan yan shan belt ordos basin chaoshui yabulai basin and northern qaidam basin forming a giant fold and thrust belt in northern china and mongolia the collision probably caused a prominent gap between late jurassic and early cretaceous magmatic episodes in the eastern caob and north china block after lasting for about 10 million years the main portion of the mongol okhotsk ocean closed forming a northeast trending suture during the early cretaceous a remnant ocean still remained in the easternmost part of the mongol okhotsk ocean and the regional compressional setting in east asia related to the closure of the mongol okhotsk ocean changed to escape tectonics driven by the collision of the lhasa block at the southern margin of asia strike slip faulting triggered gravitational collapse of upper crust and delamination of lower crust and mantle lithosphere that was thickened during the mongol okhotsk collision resulting in the development of a continental scale extensional setting in east asia associated with rift basins metamorphic core complexes and igneous rocks

twentieth century summer temperature variability in the southern altai mountains a carbon and oxygen isotope study of tree rings the altai mountains southern siberia represent an area of significant scientific interest and exceptional palaeoecological potential to assess the influence of climate on the stable isotopic composition of tree ring cellulose and the potential of this record as a palaeoclimate proxy replicated stable oxygen and carbon isotope time series were developed for the twentieth century from four siberian pine pinus sibirica du tour trees growing near the settlement of aktash russian altai mountains southern siberia bootstrapped calibrations for the local instrumental period ad 1954 2000 reveal strong correlations between summer july august growing season temperatures and tree ring oxygen r2 0 55 and carbon r2 0 30 isotopes covariance observed between both carbon and oxygen isotope data suggest a common stomatal control the resulting empirical model was used to reconstruct regional summer temperatures for the twentieth century no divergence is observed between the non detrended tree ring isot

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

determining the age distribution of colle gnifetti monte rosa swiss alps by combining ice cores ground penetrating radar and a simple flow model ice cores from cold alpine glaciers may provide unique paleoclimate information fromnon polar latitudes we explore the three dimensional internal age distribution of the small cold glaciersaddle colle gnifetti monte rosa italy switzerland to compare the age depth relations from fourlocal deep ice cores tracking isochronous refection horizons detected by ground penetrating radar gpr among the core locations reveals consistent dating up to 80 yearsbp this approach is confned torecent ages duetothelackofclearrefectionsbelowthefrn icetransition weattempttoovercomethislimitation by including a two dimensional fow model adapted to the gpr derived surface accumulationand ice thickness distribution modeled and gpr isochrones are compared indicating agreement inshape but featuring a potential offset of 0 3 5m the modeled isochrones are interpolated to the corearray with ages assigned according to the ice core datings the resulting age distribution is consistentup to 110 yearsbp with age uncertainties increasing from 7 to 80 years in the lower half of the ice this combination of methods is novel for alpine sites and may be adapted for spatial extrapolation ofice properties other than age

a novel radiocarbon dating technique applied to an ice core from the alps indicating late pleistocene ages ice cores retrieved from high altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions because of the specific flow behavior of ice their age depth relationship is nonlinear preventing the application of common dating methods such as annual layer counting in the deepest and oldest part here we present a new approach and technique allowing dating of any such ice core at arbitrary depth for the age range between 500 years b p and the late pleistocene this new complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies using small to ultrasmall sample size 100 g carbon content 5 g accelerator mass spectrometry we take advantage of the ice included water insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon 14c dating analysis and dating of the bottom ice of the colle gnifetti glacier swiss italian alps 45 55 50 n 7 52 33 e 4455 m asl has been successful in a first application and the results revealed the core to cover most of the holocene at the least with indication for late pleistocene ice present at the very bottom

ice core net snow accumulation and seasonal snow chemistry at a temperate glacier site mount waddington southwest british columbia canada a 141m ice core was recovered from combatant col 51 385 n 125 258 w 3000ma s l mount waddington coast mountains british columbia canada records of black carbon dust lead and water stable isotopes demonstrate that unambiguous seasonality is preserved throughout the core despite summer surface snowmelt and temperate ice high accumulation rates at the site 4 m ice eq a 1 limit modification of annual stratigraphy by percolation of surface meltwater the ice core record spans the period 1973 2010 an annually averaged time series of lead concentrations from the core correlates well with historical records of lead emission from north america and with ice core records of lead from the greenland ice sheet the depth age scale for the ice core provides sufficient constraint on the vertical strain to allow estimation of the age of the ice at bedrock total ice thickness at combatant col is 250 m an ice core to bedrock would likely contain ice in excess of 200 years in age accumulation at combatant col is significantly correlated with both regional precipitation and large scale geopotential height anomalies

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

pollen analysis of the 1973 ice core from devon island glacier canada abstract meltwater from a 299 m long ice core was filtered and analyzed for fossil pollen and spores pollen concentration was higher in the late holocene and interglacial intervals ca 7 liter 1 than in the early holocene and wisconsinan ca 1 2 liter 1 ones the late holocene and interglacial assemblages were dominated by alnus alder whereas the early holocene and wisconsinan ones were dominated by betula birch and artemisia sage during the holocene and probably the last interglaciation most of the pollen and spores were blown a minimum of 1000 km from low arctic shrub tundra and adjacent subarctic picea spruce forest these areas were dominated by the arctic air mass during the summer pollinating season during the wisconsinan early holocene glacier ice and arctic air were more widespread and pollen sources were more distant thus at this time relatively little pollen was incorporated into the ice the devon ice core data suggest that there should have been pollen in the continental ice sheet of wisconsin time when the ice sheet retreated this pollen would be carried by meltwater and redeposited with silt and clay together with contemporary pollen producing an ecologically anomalous assemblage

the last interglacial as recorded in the greenland ice sheet and canadian arctic ice caps abstract the greenland ice sheet and canadian arctic ice cap record of the last interglacial undertood broadly as marine isotopic stage 5 is critically reviewed lack of age control on the deep ice core records leaves open two largely different interpretations of the climate in marine isotopic stage 5 either most of stage 5 with the exception of substage 5e experienced a cold climate and the main change from interglacial to glacial conditions took place at the boundary between substages 5e and 5d or during much of stage 5 the climate was integracial type i e as warm as or warmer than at present with substage 5d as the only period with a glacial type climate it is concluded that most of the hard evidence is in favour of the latter scenario ice sheet dynamic model studies using the warm marine isotopic stage 5 scenario indicate that the greenland ice sheet in the warmest periods of stage 5 had split up into a main ice sheet covering central and northern greenland and a much smaller ice cap over the southeastern highlands the greenland record of marine isotopic stage 5 is then discussed in relation to other paleoclimatic and paleoenvironmental records the possibility of major inter hemispheric differences of the climate in mid and late marine isotopic stage 5 is discussed it is concluded that it is important to study the entire marine isotopic stage 5 not only substage 5e in order to understand possible differences in the global climatic responses to nearly indentical peaks in orbitally driven summer insolation changes in the northern hemisphere

1738 years of mongolian temperature variability inferred from a tree ring width chronology of siberian pine 1738 years ad 262 1999 of temperature variability are inferred from tree ring widths of siberian pine at solongotyn davaa sol dav a timberline 2420 m site in mongolia this chronology can account for 33 of the temperature variance from 1882 1993 the warmest conditions over the past millennium are during the 20th century the 1999 ring width has the highest index value over the past millennium both warmer and colder intervals are inferred during the medieval warm epoch the most severe cold occurred in the 19th century unusual cold and frost in ad 536 545 coincide with extremes in other proxies and historical accounts confirming a widespread catastrophic event trends resemble those of other eurasian paleoseries and hemispheric scale reconstructions over the past millennium more chronologies such as sol dav are essential to improve coverage in the uncertain earlier centuries of these reconstructions and their estimates of natural variability relative to recent anthropogenic change

report of 1st discussion group the last interglacial in high latitudes of the northern hemisphere terrestrial and marine evidence abstract the paleoclimatic informations preserved at some selected sites from high northern latitudes correlative with the last interglacial maximum of isotopic substage 5e have been compiled on a hemisphere scale the mapped compilation reveals much warmer climate conditions on average than present in both terrestrial and marine environments and indicates a northward shift of subpolar and boreal bioclimatic zones the data also suggest that temperature and precipitation gradients were significantly different than those of the holocene with particularly efficient latitudinal and eastward transport of warm air masses the paleoenvironmental and paleoclimate trends through the last interglacial sensu lato isotopic stage 5 are more difficult to assess because the chronostratigraphical framework is poorly constrained nevertheless the data suggest important regionalism in the climatostratigraphical trends in particular the large amplitude climatic cyclicity that characterizes the last interglacial of europe is barely observed elsewhere moreover by the end of the last interglacial isotopic substage 5a conditions slightly cooler than present are recorded in western europe while relatively warm conditions similar to today apparently prevailed in circumpolar regions adjacent to the north atlantic despite the onset of ice growth the last interglacial provides paleosynoptic situations unlike those of the present that may contribute to understanding interactions within the environmental system on a hemispheric scale there is however an imperative need for uniformization of data sets and for more accurate chronological control on regional scales

snow chemistry of agassiz ice cap ellesmere island northwest territories canada pit wall samples were collected from two sites about 2km apart on agassiz ice cap ellesmere island northwest territories canada in 1992 1993 and 1994 and from a site a further 1 km distant in order to study spatial and seasonal variations in snow chemistry two of the pits were dug in wind scoured zones and one in an unscoured zone although a large part of the winter snow is removed fromt he scoured zones which do not show very negarive 18 o values the winter spring anion peaks are still evident this may be due to the predominance of dry deposition in mid winter the cl and so 4 2 ions peak in later winter early spring while no 3 peaks both in later winter early spring and in summer vertical concentration profiles of all anions did not significantly alter over a 2 year period indicating that there are no serious post depositional changes due to evaporation snow melting or photochemical reactions however comparisons between stake board snow accumulation measurements and those derived from the least scoured pit indicate that a single pit will represent annual accumulation rates for a local area only

paleoenvironments of the canadian high arctic derived from pollen and plant macrofossils problems and potentials abstract analyses of peat sections lake sediments and ice cores provide information about late quaternary arctic environments palynomorphs and plant macrofossils from each of these three types of sediments record different aspects of the environment with particular spatial and temporal scales of resolution in the arctic the limits to the interpretation of past environments are particularly significant problems of low pollen concentrations long distance transport stratigraphic inversions and contamination by fossils from older deposits are more serious in this region due to the biogeographic context that characterizes these high latitudes and influences the particular ecological and geomorphological processes however recent work has shown that past environments can be reconstructed from evidence preserved in high arctic sediments and ice cores if these problems are taken into account before their interpretation

seasonal deposition of holocene banded sediments in the severn estuary levels southwest britain palynological and sedimentological evidence abstract banded sediments outcrop widely in the intertidal zone of the severn estuary and have been suggested on the basis of textural analysis to have formed in response to seasonal variations in sea temperature and windiness holocene 14 2004 536 here palynological and sedimentological analyses of banded sediments of mid holocene date from gold cliff on the welsh side of the severn estuary are combined to test and further develop the hypothesis of seasonal deposition pollen percentage and concentration data are presented from a short sequence of bands to establish whether textural variations in the bands coincide with variations in pollen content reflecting seasonal flowering patterns it is shown that fine grained band parts contain higher total pollen concentrations and a higher proportion of pollen from late spring to summer flowering plants than coarse grained band parts pollen in the coarser deposits appears primarily to reflect deposition from the buffering reservoir of suspended pollen in the estuarine water body and from rivers when there is little pollen in the air in winter while the finer sediments contain pollen deposited from the atmosphere during the flowering season superimposed on these background sources the potential of such deposits for refining chronologies and identifying seasonality of coastal processes is noted and the results of charcoal particle analysis of the bands presented as an example of how they have the potential to shed light on seasonal and annual patterns of human activity

late glacial and holocene vegetational history of the altai mountains southwestern tuva republic siberia two lakes of glacial origin grusha at 2413 m and akkol at 2204 m are located on a broad high mountain plateau on the dry eastern end of the russian altai mountains in the republic of tuva just north of mongolia the present vegetation of the area is an open high mountain tundra steppe mosaic with patches of larix and pinus sibirica forests on north facing slopes 30 km northwest of the lakes alpine meadows occur near streams and snow patches pollen diagrams and radiocarbon dates 16 for grusha and 12 for akkol were used to reconstruct the vegetational history since the last glaciation the core from grusha contains about 50 cm of late glacial sediment of relatively low organic content mostly correlated with the younger dryas episode because of the high percentages of artemisia gramineae and chenopodiaceae along with a diversity of non arboreal pollen types indicating tundra steppe and meadow steppe in the earliest holocene starting with increased organic matter at about 195 cm 12 000 cal yr bp the artemisia gramineae chenopodiaceae pollen assemblage continued along with an increase in shrub betula but without the diversity of minor non arboreal types the interpretation of dry and warm climate at this time is supported by the unconformity at akkol implying a dried lake then after about 1000 years the increase of pinus sibirica p sylvestris picea obovata and abies sibirica suggests that forests developed in response to increased humidity first at the higher elevation grusha and then at akkol after about 6000 cal yr bp the role of forests decreased sharply in the area the picea and abies components almost disappeared as they did also in more westerly areas of the altai mountains steppe elements increased along with alpine herbs especially after 2000 cal yr bp as a result of cooling or increased aridity as well as probable human activity correlation of the vegetation sequence for the tuva sites with those to the west in the central altai mountains indicates that the late glacial open landscapes persisted in the earliest holocene but then were invaded by coniferous forests as a result of increased moisture and temperature associated with atlantic storm systems as well as with insolation enhanced asian monsoon cooling and drying after about 6000 cal yr bp brought the decline of abies and picea and the expansion of tundra steppe

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