a new record of holocene climate change from the bottom sediments of lake baikal abstract detailed siliceous microfossil records diatoms and chrysophyte cysts from the bdp 93 2 borehole with resolution of ca 30 120 years were obtained from lake baikal sediments to test the sensitivity of the lake baikal system to minor climate changes during the holocene our new results demonstrate that the subboreal period is characterized by the highest accumulations of diatom frustules and chrysophyte cysts in lake baikal sediments the siliceous microfossil record suggests that the holocene climatic optimum in this interior part of asia corresponds to the subboreal period 2 5 4 5 ka and not to the atlantic period 4 6 6 ka although quite different from holocene reconstructions for the european part of eurasia the holocene sedimentary record from lake baikal shows good correlation with palynological and soil climatic records from southeast siberia and mongolia where similar responses of the terrestrial biosphere are also documented a distinctive monospecific lamina of synedra acus diatom species coincident with the maximum of chrysophyte cyst accumulation during the subboreal period argues for the possible short term changes of the trophic state of lake baikal from oligotrophic with a cold water diatom assemblage to eutrophic with a thermophilic monospecific diatom flora comparison of diatom and cyst responses provides a key to distinguishing the humidity from temperature response in future studies of high resolution records of lake baikal

organic carbon fractions and estimation of organic carbon storage in the lake sediments in inner mongolia plateau china organic carbon oc in lake sediments plays an important role in terrestrial ecosystem carbon cycle the inner mongolia plateau contains a number of shallow and freshwater lakes with a total lake area of more than 8 000 km2 accounting for an approximate 10 of the total lake area in china the inner mongolia plateau lakes act as important oc sink in mid high latitude regions in this study heavy and light fractions of oc and oc species were analyzed in sediments from four typical lakes in the inner mongolia plateau meanwhile to identify oc origins allochthonous and autochthonous oc were calculated based on a binary model furthermore total organic carbon toc storage active carbon pool acp and stable carbon pool scp over the past 150 years were estimated in the inner mongolia plateau the dominating direct findings of the current research are that heavy fraction oc plays a key role as carbon sink in mid high latitude regions due to its percentage of more than 90 in toc the percentages of allochthonous oc in toc are high 86 4 66 7 and 72 5 in daihai lake dh dalinuoer lake dlne and hulunhu lake hlh respectively which indicates that allochthonous oc is dominant in dh dlne and hlh the range of humin is 62 15 84 03 in these four lakes the average oc accumulation rate calculated in this work is 1 37 g c m 2 year 1 in these four lakes comparatively oc storages in sediments from lakes in the inner mongolia plateau are relatively more stable than from those lakes located in tropical and sub tropical regions an estimate of the toc burial scp and acp in lake sediments would be 1 64 1012 1 52 1012 and 1 20 1011 g c respectively over the past 150 years in the inner mongolia plateau

holocene climate variations retrieved from gun nuur lake sediment core in the northern mongolian plateau our pollen based climate reconstruction shows that both temperature and moisture were low during the early holocene from 10 000 to 8000 cal a bp and gradually climbed from 8000 to 6000 cal a bp the last 6000 years have been generally warm and wet with high amplitude fluctuations the high moisture conditions for the past 6000 years are not only corroborated by high arboreal pollen non arboreal ap nap trees and shrubs over herbs pollen ratio and high pollen concentration but also by high organic matter content and diatom data we suggest that lower winter insolation and remaining ice covers in the early holocene might have slowed down temperature rise in the continental interiors and that the resulted low temperature might have suppressed regional evaporation that was a major water vapor source for precipitation at the same time icemelt water injection into the north atlantic ocean might have also suppressed water vapor supplies to the downwind areas including the northern mongolian plateau

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

holocene climate change in northeastern china reconstructed from lipid biomarkers in a peat sequence from the sanjiang plain abstract lipid biomarkers extracted from a sediment peat sequence from the sanjiang plain were analyzed to assess the change in regional vegetation and climate during the last 8 ky the combination of n alkane and n alkanoic acid distributions and published pollen and plant macrofossil records for the lake sediments underlying the peat reveal that the region experienced a warmer and wetter period before ca 6 ka that corresponds to the monsoon maximum and holocene climate optimum in northeast china the climate then entered a cold and wet period from 6 to 4 ka a shift to warmer and drier conditions starting 4 ka is recorded as a transformation from a shallow lake to a peat deposit from 1 5 to 0 4 ka the region entered a cold and wet period that was followed by warm and dry conditions for the most recent 0 4 ky our lipid based paleoclimate reconstruction was compared with holocene reconstructions based on lipid records from the nearby hani peat sequence peat cellulose 13c results from the jinchuan peat sequence and pollen records from other lakes in northeast china most of the regional paleoclimate changes reconstructed from the lipid proxies in the sanjiang plain peat sequence have a strong link with sea surface temperature changes in the sea of japan that were influenced by summer solar insolation at 65 n and the east asia summer monsoon in contrast the change to the warmer and drier conditions of the last four centuries seems to be mainly a consequence of human activity

paleomagnetism of the central metasedimentary belt grenville province ontario differential uplift or collision of terranes abstract a paleomagnetic traverse across the central metasedimentary belt of the precambrian grenville province in southern ontario linked to an earlier study of the adjoining central gneiss belt sampled 54 sites in the frontenac sharbot lake mazinaw elsevir and bancroft terranes 40 ar 39 ar thermochronometry indicates differential unroofing of these terranes with slow cooling 1 0 1 5 c ma along parallel temperature time paths presently exposed rocks cooled through 500 c around 1100 ma frontenac 1010 ma elsevir 960 ma central metasedimentary belt boundary zone and 930 ma mazinaw cosca m a sutter j f essene e j 1991 cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40 ar 39 ar thermochronology tectonics 10 1991 959 977 1100 930 ma was a time of rapid paleolatitude shift but the various terranes do not have distinct paleomagnetic signatures frontenac sharbot lake and mazinaw terranes have similar reverse polarity paleopoles in the central part of the grenville polar wander track frontenac and sharbot lake normal poles are typical 1000 ma grenville a poles while mazinaw normal poles seem to be somewhat older frontenac poles bear no resemblance to 1100 ma keweenawan poles the elsevir pole and some frontenac poles resemble grenville b poles 600 800 ma although 40 ar 39 ar hornblende ages were reset thermally between 1100 and 930 ma during differential uplift of terranes the terranes were not remagnetized at these same times frontenac sharbot lake and mazinaw terranes like much of the boundary zone and the central gneiss belt seemingly were all remagnetized between 1000 and 900 ma perhaps by a widespread thermochemical event a 600 800 ma event affected elsevir and part of the frontenac at the western and eastern extremes of the traverse but not areas between the lack of correlation between 40 ar 39 ar ages and paleomagnetic results for the frontenac sharbot lake mazinaw and elsevir casts doubt on the thermochronometric age calibration of the grenville apparent polar wander path which is based on the assumption that the magnetic and isotopic systems respond in similar ways to slow cooling during uplift so that their blocking temperatures can be directly compared the most discordant results those of the frontenac could be reconciled if the frontenac terrane acquired its a magnetization around 1100 ma before it docked with laurentia this is geologically plausible but the match between the frontenac poles and 900 1000 ma grenvillian poles seems too close to be coincidental

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

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

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

mid to late holocene climate change in north central mongolia as recorded in the sediments of lake telmen abstract a record of climatic change has been reconstructed for the past 7110 calibrated calendar cal years for lake telmen mongolia based upon sedimentologic and geomorphic evidence from the lake watershed system lake telmen is a saline presently 4 g l 1 closed basin lake and is therefore sensitive to changes in effective moisture balance between 7110 and 6260 cal yr ago conditions in the lake telmen region were hyperarid and a small saline approximately 20 g l 1 lake was present increased effective moisture balance but still arid conditions prevailed between 6260 and 4390 cal yr ago since 4390 cal yr ago generally more humid conditions prevailed in the lake telmen region as the lake deepened a hypoxic hypolimnion became established below a well developed summer thermocline resulting in varved sediment accumulation since 4390 cal yr ago between about 2710 and 1260 cal yr ago a greater than present day effective moisture balance is recorded by a series of four lake highstand terraces sedimentologic profiles from lacustrine cores suggest an increase in effective moisture during the past approximately 680 cal yr

multivectorial paleointensity determination from the cordova gabbro southern ontario abstract we report geomagnetic field intensities for the a 1000 ma and b 850 ma natural remanent magnetizations of the cordova gabbro of southern ontario we interpret a and b to be secondary thermal overprints produced during regional uplift and cooling following the grenvillian orogeny multivectorial a b paleointensity data were analyzed using pairs of arai diagrams for the separated a and b vectors from 18 reliable a results and 15 reliable b results we find paleofield values of 18 1 2 1 t and 7 1 1 5 t respectively the corresponding virtual axial dipole moments vadms are 3 12 0 36 and 1 82 0 38 10 22 a m 2 about 70 and 40 of the average phanerozoic dipole moment based on data from 0 3 300 ma the cordova data and other precambrian paleointensities are generally within a range of approximately 0 5 1 5 times the phanerozoic mean vadm three sets of paleofield values as a function of paleolatitude including the cordova data support a dipole configuration for the earth s field in 25 150 ma time windows around 2700 ma 1100 ma and 850 ma

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

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

holocene moisture variations across china and driving mechanisms a synthesis of climatic records based on the review of 33 holocene moisture reconstructions that passed quality scrutiny temporal and spatial patterns of regional moisture variations are delineated the regionally averaged moisture index from xinjiang demonstrates that the moisture index has been persistently climbing since 10 ka cal bp and that the period between 4 and 0 ka cal bp is the holocene moisture optimum comparison of the moisture index of xinjiang region with the winter climate of northern europe leads us to propose that the holocene moisture variations in xinjiang region have been controlled by the winter temperature variations in the north atlantic region the regionally averaged moisture index from the tibetan plateau shows that the moisture has been persistently declining since 11 ka cal bp and that the period between 11 5 and 7 5 ka cal bp was the holocene moisture optimum the parallel trends between the moisture level in the tibetan plateau and the indian summer monsoon strength retrieved from the arabian sea suggest that the tibetan plateau has been under influence of the indian summer monsoon throughout the holocene the regionally averaged moisture index curves from northern china and southern china are the delayed reflections of the east asian summer monsoon strength to the solar radiation that is the peak insolation was responded by the holocene oceanic thermal optimum with significant time lags and the oceanic thermal optimum was then responded by the holocene moisture optimum in southern china and northern china also with some time lags the differences in the moisture index curve shapes and in the durations of the holocene moisture optimum between northern china and southern china suggest that the strength of the east asian summer monsoon had gradually transgressed northward in the early holocene and gradually regressed southward in the late holocene

the assessment of localized remobilization and geochemical process of 14 metals at sediment water interface swi of yingkou coast china by diffusive gradients in thin films dgt a passive sampling technique diffusive gradients in thin films dgt was used to determine profiles of 14 metals on fine scale at swi of two sites in yingkou coast and to investigate biogeochemical process of mn fe and other metals based on dgt concentration flux and biogeochemical mechanism remobilization character of metals in sediment profile was studied both profiles of two sites indicated sharp peaks of fe and mn at anoxic sediment which verified redox process of fe mn with large fluxes especially very large peaks of mn at 9 75 cm 7 239 10 4 g cm 2 s 1 and fe at 9 25 cm 1 420 10 3 g cm 2 s 1 at site 2 corresponding with sulfide concentrations at same depths in profile were used for the calculation of saturation index to assess the solubility of metal sulfide other metals in certain segments of profiles at two sites indicated coupled geochemical process between them and fe mn dgt probe should be a reliable tool to measure multi metals in sediment porewater and to assess geochemical process in coastal area

late holocene vegetation and climate change in jeju island korea and its implications for enso influences abstract several recent studies suggest the hypothesis that the el nino southern oscillation enso is an important factor controlling the holocene east asian monsoon eam however the mechanism underlying this influence remains unclear due to the lack of high resolution paleoclimate records from the coast of east asia here we provide a new record of late holocene climate change in coastal east asia based on multi proxy evidence pollen organic content magnetic susceptibility grain size obtained from a sediment core from jeju island south korea as jeju island is strongly influenced by the kuroshio flow our sediment proxy records contain enso signals from the tropical pacific the study area was affected by dry cool conditions in the western tropical pacific wtp between 4350 and 1920 cal yr bp when el ninos were frequent and by rapid warming wetting and forestation since 1920 cal yr bp when la ninas were more common jeju island was relatively dry cool between 2100 and 1600 1300 1200 1100 1000 800 650 and 300 50 cal yr bp as opposed to the galapagos islands which were relatively wet warm reflecting the enso related negative correlation between eastern and western margins of pacific wet conditions may have prevailed during the early little ice age lia 620 280 cal yr bp despite consistent cooling this period of high precipitation may have been associated with the increased landfall of typhoons and with warmer kuroshio currents under la nina like conditions according to our results eam on the east asian coastal margin was predominantly driven by enso activity rather than by the precession effect paleoclimatic data from jeju island with its insular position and closeness to warm kuroshio currents provide clear evidence of these enso influences

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

abrupt early to mid holocene climatic transition registered at the equator and the poles paleoclimatic records from equatorial east africa antarctica and greenland reveal that atmospheric circulation changed abruptly at the early to mid holocene transition to full postglacial conditions a climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world

calcite graphite isotope thermometry in amphibolite facies marble bancroft ontario this study presents calcite graphite carbon isotope fractionations for 32 samples from marble in the northern elzevir terrane of the central metasedimentary belt grenville province southern ontario canada these results are compared with temperatures calculated by calcite dolomite thermometry 15 samples garnet biotite thermometry four samples and garnet hornblende thermometry three samples cal gr values vary regularly across the area from 6 5 in the south to 4 0 in the north which corresponds to temperatures of 525 c in the south to 650 c in the north previous empirical calibration of the calcite graphite thermometer agrees very well with calcite dolomite garnet biotite and garnet hornblende thermometry whereas theoretical calibrations compare less well with the independent thermometry isograds in marble based on the reactions rutile calcite quartz titanite and tremolite calcite quartz diopside span temperatures of 525 600 c and are consistent with calculated temperature x co2 relations results of this study compare favourably with large scale regional isotherms however local variation is greater than that revealed by large scale sampling strategies it remains unclear whether the temperature cal gr relationship observed in natural materials below 650 c represents equilibrium fractionations or not but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble

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

holocene climate changes in the mid high latitude monsoon margin reflected by the pollen record from hulun lake northeastern inner mongolia pollen assemblage data from a sediment core from hulun lake in northeastern inner mongolia describe the changes in the vegetation and climate of the east asian monsoon margin during the holocene dry steppe dominated the lake basin from ca 11 000 to 8000 cal yr bp suggesting a warm and dry climate grasses and birch forests expanded 8000 to 6400 cal yr bp implying a remarkable increase in the monsoon precipitation from 6400 to 4400 cal yr bp the climate became cooler and drier chenopodiaceae dominated the interval from 4400 to 3350 cal yr bp marking extremely dry condition artemisia recovered 3350 2050 cal yr bp denoting an amelioration of climatic conditions both temperature and precipitation decreased 2050 to 1000 cal yr bp as indicated by decreased artemisia and the development of pine forests during the last 1000 yr human activities might have had a significant influence on the environment of the lake region we suggest that the east asian summer monsoon did not become intensified until 8000 cal yr bp due to the existence of remnant ice sheets in the northern hemisphere changes in the monsoon precipitation on millennial to centennial scales would be related to ocean atmosphere interactions in the tropical pacific

lacustrine and eolian records of holocene climate changes in the mongolian plateau preliminary results abstract this study compares two pairs of adjacent lacustrine and eolian sections at sites in the southern and northern mongolian plateaus in order to test spatial climate variability during the holocene based on the lithology proxy data and 14 c dated and the interpolated ages the following observations can be made in the northern mongolian plateau a best developed holocene paleosol dated at 8672 14 c yr bp at the shaamar section and the carbonate rich laminated layer in the gun nuur lake core mark the interval of warmer and dryer climate during the early holocene younger paleosols at the shaamar section and corresponding organic rich layers in the gun nuur core were formed under distinctly cooler and more humid conditions the baahar nuur lake core in the southern mongolian plateau and the dingxi type section in the northern part of the western chinese loess plateau appear to indicate that a prolonged interval of maximum humidity prevailed in this region during the early and mid holocene 9000 4000 14 c yr bp by contrast in the northern mongolian plateau the most humid conditions seem to have occurred from 4500 to 2500 possibly to 1650 14 c yr bp this discrepancy implies that the concept of the holocene climatic optimum has limitations and may have to be reconsidered if it is intended to have a large scale connotation

linkage between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary abstract knowledge of the role of c4 vegetation expansion in regulating dune stabilization during the late quaternary is important for understanding the evolution of the environment and climate in the climatically sensitive margin of the east asian summer monsoon however due to the lack of both reliable vegetation records and chronological control during episodes of dune activity the relationship between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary remains unclear here we present a new regional compilation of late quaternary stable carbon isotopic data from organic matter together with dated records from sub aerial sedimentary deposits in the region our compilation of vegetation development and dune activity in these deserts suggests that c4 vegetation expansion with a main contribution from chenopodiaceae and a secondary contribution from poaceae and cyperaceae may have played a critical role in dune semi stabilization with a northwestward trend from 13 to 9 ka and dune stabilization throughout the entire study region from 9 to 5 ka in addition during the late holocene intensified millet cultivation or overgrazing and or climatic deterioration at 1 5 ka likely caused an increase in c4 vegetation abundance in the deserts of ne china which is associated with a dune mobilization episode in contrast after 2 5 ka decreased vegetation cover and dune mobilization in the mu us and hobq deserts were likely caused by poor land use practices and historically documented droughts overall c4 vegetation expansion was the main cause of dune stabilization in these deserts during the late quaternary

holocene climatic reconstructions from the fossil pollen record at qigai nuur in the southern mongolian plateau this study focuses on the reconstructions of vegetation and climate changes during the past 11 000 years on the basis of 222 fossil pollen samples from qigai nuur core qgn 2004 in the southern p

optical dating of holocene dune sands from the hulun buir desert northeastern china aeolian deposits from the hulun buir desert of northeastern china are studied with optically stimulated luminescence dating methods to establish the chronology of dune building phases and climatic changes since the last deglaciation our results indicate that wet climate marked by dune stabilization and soil development in the hulun buir desert commenced at 11 ka ago and this early episode of dune stabilization lasted until 4 4 ka ago this optimum climate between 11 and 4 4 ka ago is mostly the response to the strengthened monsoon circulation and increased precipitation in the northern hemisphere the environment generally became arid after 4 4 ka ago but the dry climate was interrupted by three phases of weak soil development occurring at 1 8 1 4 1 2 1 0 and 0 84 0 5 ka ago respectively such short events of dune stabilization were associated with the warm and humid climate in historical time however the present dune mobilization in the hulun buir desert is mainly the result of poor la

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the relation between iron formation and low temperature hydrothermal alteration in an archean volcanic environment abstract the uppermost section of the hunter mine group hmg 2728 ma a bimodal volcanic complex in the abitibi greenstone belt contains both oxide and carbonate facies banded iron formation bif this paper explores the relationship between volcanic activity and the development of the two types of iron formation the oxide facies represented by chert jasper magnetite iron formation is widespread and recurs at several stratigraphic levels field evidence suggests it deposited directly on the sea floor during periods of volcanic quiescence and is most probably derived from fluids seeping from volcaniclastic sediments and the compaction of felsic shard rich tuffs seeping occurred along synsedimentary and synvolcanic faults and then along bedding planes carbonate siderite facies iron formation in contrast formed locally below a silica cap rock by in situ low temperature hydrothermal replacement of chert tuff beds and even of the oxide formation thus the two types of iron formation although spatially and stratigraphically juxtaposed are not the result of the same process and only the carbonate facies appears to be directly related to a low temperature hydrothermal volcanic process the contrasting genesis of oxide and carbonate iron formations indicates that current simplistic models relating banded iron formation to volcanic massive sulphide deposits need to be re evaluated the notion that oxide iron formation represents a distal manifestation of volcano generated hydrothermal activity may be the exception and not the rule because as indicated by this study bif occurs in the central part of a volcanic edifice rather than on the flanks

mid to late holocene climate evolution of the lake telmen basin north central mongolia based on palynological data abstract palynological and sedimentological data from lake telmen in north central mongolia permit qualitative reconstruction of relative changes in moisture balance throughout the mid to late holocene the climate of the atlantic period 7500 4500 yr ago was relatively arid indicating that lake telmen lay beyond the region of enhanced precipitation delivered by the expanded asian monsoon maximum humidity is recorded between 4500 and 1600 cal yr b p during the subboreal 4500 2500 yr ago and early subatlantic 2500 yr present periods additional humid intervals during the medieval warm epoch 1000 1300 a d or 950 650 ago and the little ice age 1500 1900 a d or 450 50 yr b p demonstrate the lack of long term correlation between temperature and moisture availability in this region a brief aridification centered around 1410 cal yr b p encompasses a decade of cold temperatures and summer frost between a d 536 and 545 1414 1405 yr b p inferred from records of mongolian tree ring widths these data suggest that steppe vegetation of the lake telmen region is sensitive to centennial and decadal scale climatic perturbations

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

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

pollen reconstruction and vegetation dynamics of the middle holocene maximum summer monsoon in northern china abstract understanding the evolution of the holocene east asian summer monsoon easm and vegetation response regimes can help predict the climatic variability and vegetation change of future warming here we reconstructed holocene vegetation and climate change based on pollen grain size and percent organic matter from a lake sediment profile in huitengxile plateau of central inner mongolia northern china we found that temperate deciduous forest steppe and temperate mixed forest steppe prevailed under maximum easm during the middle holocene 8 3 5 9 cal kyr bp with more open vegetation and a weak easm prior to and following this period the vegetation succession is consistent with regional records suggesting a regional vegetation pattern i e oak forest replacing birch and elm forest during the middle holocene and pine forest expanding at the expense of birch and oak forest since 6 0 cal kyr bp a regional synthesis suggests the maximum easm began at 8 3 7 8 cal kyr bp in northern china indicating a significant delay when compared with published records from southern china the maximum easm in northern china ended at 5 9 5 5 cal kyr bp being similar or slightly delayed from that in southern china

methane gas release from the storegga submarine landslide linked to earlyholocene climate change a speculative hypothesis the 3000 km3 storegga submarine landslide occurred c 8150 years ago from an area rich in gas hydrates off the western coast of norway a synchronous increase of 80 100 ppb in atmospheric methane c

history of moisture change indicated by aeolian deposit in the horqin sandy land northeastern china since the last glacial maximum abstract the horqin sandy land located in the monsoonal boundary of northeastern china is sensitive to the vicissitudes of the asian monsoon am the aeolian sand paleosol sequences in this area especially since the last glacial maximum lgm have preserved valuable geological archives indicating the history of humidity changes in the region however existing studies on the local humidity rhythms have not been sufficient to reach a consensus in a relatively in depth study of the forcing mechanism we present the results of a systematic optically stimulated luminescence osl chronology and detailed multi proxy analyses of the grain size geochemical elements magnetic susceptibility and organic matter since the lgm the results demonstrate that the humidity gradually increased from the lgm to the middle holocene reaching optimum humidity around 9 3 ka despite intense oscillations occurring during 6 5 ka that is largely consistent with other paleoenvironmental records from ne china it is suggested that the variation in the humidity is basically controlled by the solar driven monsoonal precipitation which is the most dominant moisture source the coupled atmosphere pacific ocean system and the westerlies could have both disturbed the monsoon precipitation thus indirectly affecting the humidity of the sandy land during the late holocene human occupation also played a significant role in the re activation of dunes

grenvillia and laurentia a precambrian wilson cycle john tuzo wilson coined the term plate in plate tectonics he is famous for inventing transform boundaries hot spot tracks and the wilson cycle of ocean birth growth and decline less well remembered is his work in the 1950s on tectonic and radiometric age provinces of the canadian shield as part of which he fathered u pb geochronology in canada this work gave strong support to the notion of continental growth through accretion of successively younger terranes onto an ancient cratonic core the present paper reviews how paleomagnetism can trace the motions of continents to test wilson s ideas continental accretion often involves deep burial of one of the colliding elements through subduction or crustal underplating such was the case with the grenville orogen and its subprovinces in their proterozoic accretion onto the laurentian craton the resulting heating and metamorphism erases most pre collisional magnetic information but adds something new the possibility of following the post metamorphic

millennial scale environmental changes in the asian monsoon margin during the holocene implicated by the lake evolution of huahai lake in the hexi corridor of northwest china the pattern of holocene environmental changes in the asian monsoon margin on a millennial timescale remains controversial based on lithological characteristics and sedimentological proxies we reconstructed holocene effective humidity changes and the lake evolution of huahai lake in the marginal area of the asian monsoon in the hexi corridor of nw china our results show that alluvial and aeolian deposition before 10 4 cal ka bp indicate an arid environment that lacustrine deposition from 10 4 to 8 8 cal ka bp indicates a transition from an arid to a humid environment and that lacustrine deposition from 8 8 to 5 5 cal ka bp occurred during the most humid conditions indicated by proxy records grain size carbonate toc and c n after 5 5 cal ka bp a depositional hiatus implicates an arid environment in the late holocene holocene environmental changes on millennial timescales in huahai lake imply that climate was arid to humid in the early holocene most humid in the mid holocene and arid in the late holocene these moisture changes were influenced by the asian monsoon particularly the transportation of water vapor by the indian monsoon in addition these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid holocene the most humid conditions that occurred in the study area during the mid holocene may have been caused by strong westerlies and low levels of evaporation

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

mineralogy and carbonate geochemistry of the dali lake sediments implications for paleohydrological changes in the east asian summer monsoon margin during the holocene abstract hydrological variations in individual plateau lakes respond from both local hydrological processes and regional climatic changes this study presents high resolution absolutely dated records of minerals in bulk samples and elements and stable isotopes of endogenic calcites from a sediment core from dali lake in inner mongolian plateau aiming to investigate the patterns and mechanisms of holocene hydrological and climatic changes in the modern northern margin of the east asian summer monsoon easm increases in the percentages of allogenic minerals quartz microcline and albite and decreases in the percentages of endogenic authigenic minerals calcite mg calcite and gypsum together with decreases in the values of ca and mg concentrations and 18o and 13c of endogenic calcites indicate an excess of water input to the lake over evaporative losses and vice versa these data suggest that the hydrological balance of dali lake was controlled by strong evaporation before 9800 cal yr bp and then the lake was supplied by significantly increased inflowing water between 9800 and 5900 cal yr bp from 5900 to 4850 cal yr bp the water input to the lake significantly decreased since 4850 cal yr bp the inflowing water maintained a low level in addition the distinct characteristics of mineralogy and carbonate geochemistry of the dali lake sediments during the periods of high lake level between 9800 7700 and 7700 5900 cal yr bp imply that the lake was mainly fed by snow ice melt water in the former period and then by regional precipitation in the latter period which was further supported by the pollen records from the same sediment core these results suggest that holocene hydrological variations in the easm margin were closely related to changes in regional temperature and precipitation which were ultimately controlled by changes in the northern hemisphere summer insolation northern high latitude ice sheets global sea level and physicochemical conditions of the north atlantic and western tropical pacific on orbital and millennial timescales the datasets in this study support that the maximum easm intensity occurred during the middle holocene in the northern easm regions

holocene environmental changes in bangong co basin western tibet part 2 the pollen record abstract a better knowledge of environmental variations in key regions such as the tibetan plateau which plays a fundamental role in the indian monsoon dynamics and thus on the whole northern hemisphere atmospheric circulation is of great importance we present here a detailed paleoenvironmental study based on pollen analyses of a sediment core from lake bangong results on the modern pollen rain are also discussed as they give valuable information for the interpretation of the fossil pollen data the pollen results of the bangong sequence and their paleoclimatic interpretation are integrated into a chronological framework on the basis of palynostratigraphical methods because of dead carbon in the lake system it has been difficult to establish a reliable chronology of the bangong sequence using a geochemical model for correcting measured 14c ages the pollen record from lake bangong compares well with the record from lake sumxi in western tibet lake bangong core provides a continuous holocene pollen record before 9600 yr b p the dominance of desertic elements in the pollen record reflects an arid environment at about 9600 yr b p an abrupt shift to steppe vegetation suggests the onset of moister conditions and from 9500 to 6200 yr b p proxy data indicate conditions warmer and wetter than today proxy data also indicate short term changes during this interval climate instability is suggested by the development of a local palustral flora which peaks at 7700 yr b p and is interpreted as a lake regression in phase with increase in the percentage of littoral and saline water diatom species between 8600 and 7700 yr b p the first humid pulse culminating at 9000 8500 yr b p is thus followed by drier conditions around 8000 7700 yr b p the interval between 7200 and 6500 yr b p regarded as optimal for vegetation growth from the pollen record corresponds to a second humid pulse a trend towards aridity is observed during the following period with dry events centered around 5500 3900 3200 and 700 yr b p

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions