sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

july temperature during the second millennium reconstructed from idaho tree rings an 858 year proxy record of july temperature for east central idaho shows multi decadal periods of extreme cooling centered around ad 1300 1340 1460 and after ad 1600 these cold intervals are interrupted by prolonged warm spells in the early 1400s late 1500s and in the 1930s the spatial signature of the paleoclimate record is centered on the north central rockies and central great plains and expands over north america following a wave like pattern neither instrumental nor proxy data in idaho northeast valleys show unusual warming during the twentieth century climate episodes over the last three centuries are in broad agreement with the greenland borehole temperature history low frequency patterns are consistent with other northern hemisphere tree ring records for the late holocene and provide a chronology of warm and cold intervals during the little ice age

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

holocene millennial scale vegetation changes in the yugu floodplain kongju area central south korea abstract to understand vegetation responses to past climate change on millennial timescales the holocene record of floodplain vegetation change in central south korea was reconstructed using the stable isotopic composition 13 c and pollen in buried soils low volume overbank deposition of fine grained alluvium by yugu stream over the past 10 000 years has produced a sequence that is well suited for 13 c analysis of soil organic matter the 13 c values varied between 25 and 20 during the holocene showing significant millennial scale fluctuations in five stages 11 000 8900 cal bp 8900 6100 cal bp 6100 3300 cal bp 3300 1200 cal bp and 1200 cal bp to present the abundance of c 4 plants estimated from a binary mixing model changed from approximately 17 57 during the stages from 3300 to 1200 cal bp and from 8900 to 6100 cal bp c 4 plant abundance and the percentage of arboreal pollen were high but the percentage of spores mainly moss and the freshwater algal sum were low indicating more arid environments temporal comparison of c 4 plant abundance change during the holocene with other reconstructed climate data from east asia suggests that millennial scale vegetation change or aridity change in central south korea was generally more synchronous with regional climate change during the late holocene than during the early to mid holocene this study suggests that the past vegetation in the yugu area has evolved in response to summer monsoon intensity in a non linear manner

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

origin and weathering properties of loess paleosol sequence in the goseong area on the east coast of south korea abstract this study aims to investigate the origin and weathering properties of the loess paleosol sequence in the goseong area on the east coast of south korea and to discuss the local sediment inputs and their paleoclimatic implications the geochemical properties suggest that the largest proportion of the sequence originated from the chinese loess plateau and or its source areas with a smaller quantity originating from the weathering products of the bedrock around the section although its origin can be regarded as the chinese loess plateau and or its source areas the sequence shows more weathered features than the chinese loess plateau moreover the weathering environments in south korea were different from those in the chinese loess plateau the difference in weathering properties may be attributed to the more humid climatic conditions in south korea the abundance of local sediment input to the sequence was controlled by sea level fluctuations in the east sea of korea and the global ice sheet developments during the glacial and interglacial cycles in the quaternary because local sediment occupies only minor proportions in the sequence the monsoon and westerly circulations in northeast asia played an important role in the loess formations in south korea as well as in the chinese loess plateau

grain size and accumulation rate records from late cenozoic aeolian sequences in northern china implications for variations in the east asian winter monsoon and westerly atmospheric circulation we attempt to reconstruct the history of westerly and monsoonal circulations in northern china using variations in sediment grain size and accumulation rate at four loess sections in the central chinese loess plateau the initiation of aeolian accumulation at about 7 6 ma in the main part of the chinese loess plateau probably marked the onset of the monsoonal circulation both the monsoonal and westerly circulations weakened from 7 6 to 5 2 ma subsequently the monsoonal circulation strengthened progressively from 5 2 ma to the present in addition the westerly circulation strengthened from 5 2 to 0 6 ma but then weakened thereafter and especially during the last 0 6 ma comparison of our aeolian records and the deep sea sediment record suggests that the strengthening trends of the monsoonal and westerly circulations were associated with the progressive development of global ice sheets during the late cenozoic abrupt changes of both the monsoon and westerly circulations occurred at 7 6 3 4 and 1 2 0 9 ma together with a weakening trend of the westerly circulation in the last 0 6 ma and are interpreted as the consequence of the episodic uplift of the tibetan plateau spatial differences in the grain size characteristics amongst the four sections suggest that the circulation intensity and variability decreased from west to east across the loess plateau due to the topographic effect of the tibetan plateau in addition some spatial differences may have been the result of local topographic effects c 2008 elsevier b v all rights reserved

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

groundwater discharge to a gobi desert lake during mid and late holocene dry periods abstract high levels of lake eastern juyanze and a wetter climate in the gobi desert nw china were recorded between 5100 and 4100 cal year bp from ostracod distribution shell geochemistry sedimentology and palynological data after about 4100 cal year bp lake levels decreased and groundwater discharge became dominant source of water during short term regressive events at about 4000 3800 and 3500 cal year bp as suggested by a significant difference in modern river water and groundwater chemistry and the geochemical signal of fossil ostracod shells the overall trend towards lower lake levels culminated in repeated episodes of desiccation of lake eastern juyanze between 3200 and 2900 cal year bp individual regressive events as well as the rapid environmental fluctuations of lake eastern juyanze at about 3000 cal year bp were likely caused by mid to late holocene temperature fluctuations recorded by the dunde ice core yao t thompson l g 1992 trends and features of climatic changes in the past 5000 years recorded by the dunde ice core annals of glaciology 16 21 24 and shifts of the southeastern asian monsoon

reconstructing dust storm frequency in china since 1617 ce using coral based estimates of sea surface temperature abstract dust storms occur frequently in arid and semi arid regions of china and other parts of the world exerting a considerable influence on air quality in densely populated areas instrumental observations of dust storms are only available over the past 50 to 60 years limiting our ability to understand dust storm variability over longer timescales however tropical sea surface temperatures have been reconstructed over the past four centuries using geochemical records from corals here we show that tropical pacific sea surface temperatures as recorded by corals can be used to reconstruct dust storm frequency at one year resolution based on the coral reconstructed annual sea surface temperature anomaly data from two regions the western pacific 25 n 25 s 110 155 e and the eastern pacific 10 n 10 s 175 e 85 w published by tierney et al 2015 we reconstructed the frequency of dust storms in northern china dsfcn for the period from 1617 to 1953 ce the reconstructed dsfcn variation can be divided into several distinct periods 1 dsfcn increased from 1617 to 1650 then 2 decreased from 1650 to 1675 3 remained unchanged from 1675 to 1755 4 increased again from 1755 to 1860 5 remained unchanged from 1860 to 1925 and finally 6 decreased rapidly from 1925 to 1995 we propose the following causal chain to explain the observed relationship between dsfcn and sst as tropical pacific ocean sst increases the siberian high weakens and the eastern asian trough strengthens as the air pressure difference weakens the east asian winter monsoon weakens and strong wind frequency decreases causing dsfcn to decrease as well the statistical results support this interpretation of the causal chain

improving a tree ring reconstruction from west central scandinavia 900 years of warm season temperatures dendroclimatological sampling of scots pine pinus sylvestris l has been made in the province of jamtland in the west central scandinavian mountains since the 1970s the tree ring width trw chronology spans several thousand years and has been used to reconstruct june august temperatures back to 1632 bc a maximum latewood density mxd dataset covering the period ad 1107 1827 with gap 1292 1315 was presented in the 1980s by fritz schweingruber here we combine these historical mxd data with recently collected mxd data covering ad 1292 2006 into a single reconstruction of april september temperatures for the period ad 1107 2006 regional curve standardization rcs provides more low frequency variability than non rcs and stronger correlation with local seasonal temperatures 51 variance explained the mxd chronology shows a stronger relationship with temperatures than the trw data but the two chronologies show similar multi decadal variations back to ad 1500 according to the mxd chronology the period since ad 1930 and around ad 1150 1200 were the warmest during the last 900 years due to large uncertainties in the early part of the combined mxd chronology it is not possible to conclude which period was the warmest more sampling of trees growing near the tree line is needed to further improve the mxd chronology

cycles and shifts 1 300 years of multi decadal temperature variability in the gulf of alaska the gulf of alaska goa is highly sensi tive to shifts in north pacific climate variability here we present an extended tree ring record of january september goa coastal surface air temperatures using tree ring width data from coniferous trees growing in the mountain ranges along the goa the reconstruction 1514 1999 based on living trees ex plains 44 of the temperature variance although as the number of chronologies decreases back in time this value decreases to and remains around 30 before 1840 verification of the calibrated models is however robust utilizing sub fossil wood we extend the goa reconstruction back to the early eighth century the goa reconstruction correlates significantly 95 cl with both the pacific decadal oscillation index 0 53 and north pacific index 0 42 and therefore likely yields important information on past climate variability in the north pacific region intervention analysis on the goa reconstruction identifies the known twentieth century climate shifts around the 1940s and 1970s al though the mid 1920s shift is only weakly expressed in the context of the full 1 300 years record the well studied 1976 shift is not unique multi taper method spectral analysis shows that the spectral properties of the living and sub fossil data are similar with both records showing significant 95 cl spectral peaks at 9 11 13 14 and 18 19 years singular spectrum analysis identifies in order of importance significant oscillatory modes at 18 7 50 4 38 0 91 8 24 4 15 3 and 14 1 years the amplitude of these modes varies through time it has been suggested minobe in geo phys res lett 26 855 858 1999 that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal 50 4 years and bi decadal 18 7 years oscillatory modes removal of these two modes of variance from our goa time series does indeed remove the twentieth century shifts but many are still identified prior to the twentieth century our analysis suggests that climate variability of the goa is very complex and that much more work is required to understand the underlying oscillatory behavior that is observed in instrumental and proxy records from the north pacific region

middle holocene environmental change in central korea and its linkage to summer and winter monsoon changes to trace the surficial responses of lowlands to past climate change we investigated 13c in total organic carbon toc c n ratios magnetic susceptibility ms and silicon si intensity directly proportional to concentration in wetland sediments collected from the gimpo area of central korea covering 6600 4600 cal yr bp two organic layers with high toc negatively depleted 13ctoc values 27 to 29 low ms values and low si intensities were found at 6200 5900 and 5200 4800 cal yr bp respectively these middle holocene wet periods corresponded to relatively intensified summer monsoon and solar activity periods the intervening dry period 5900 5200 cal yr bp with high ms high si and low toc corresponded to an intensified dust activity interval and stronger winter monsoon this multi centennial climatic fluctuation of wet periods 6200 5900 cal yr bp and 5200 4800 cal yr bp and an intervening dry period 5900 5200 cal yr bp in central korea was more synchronous with climate change in the arid inner part of china than with that in south china suggesting possible strong high latitude driven climatic influences e g north atlantic cooling events during the middle holocene

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

fine aeolian quartz records in cheju island korea during the last 6500 years and pathway change of the westerlies over east asia 1 we investigated the fine component of aeolian dust deposited on a maar of cheju island korea during the last 6500 years to specify the variability of fine aeolian dust transported by the westerlies and its main controlling factor from the viewpoint of global atmospheric circulation as a proxy for the fine aeolian dust we used the fine component of chemically isolated aeolian quartz from bulk sediments the fine quartz flux fqf varies from 0 1 to 1 4 mg cm2 a with periodicities of 1620 810 400 325 and 210 years mainly providing information on the aridity change in the dust source region the taklimakan desert the median grain size of the fine quartz mfq representing the pathway of the dust transporting westerlies fluctuates between 2 and 6 m with significant cycles of 1030 390 280 220 and 195 years and shows similar variation pattern to the fqf on the basis of visual and spectral analyses the high low fqf and the large small mfq correspond to the warm cold atmospheric temperature record from greenland ice cores with significant coherent cycles indicating that the aridity in the dust source areas and the pathway of the westerlies in east asia were linked to climatic and atmospheric conditions in greenland through the pathway change of the westerlies during the middle to late holocene the pathway change of the westerlies mainly responsible for the variability of the fine aeolian dust in east asia was probably controlled by a climatic response to initial solar activity and resulting atmospheric reorganization in polar and high latitude regions

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

holocene dust deposition in the ili basin and its implications for climate variations in westerlies dominated central asia abstract understanding holocene paleoclimate in arid central asia aca is helpful for predicting future climate however holocene climate patterns and their forcing mechanisms across aca are vigorously debated in the context of global climate change here we present a holocene loess profile sgx from the ili basin in the westerlies dominated central asia based on high resolution medium grained 38 63 m quartz optically stimulated luminescence osl dating and grain size and color measurements we reconstruct the holocene paleoclimate osl geochronology indicate that this sgx loess profile covers the last 11 5 ka and grain size analyses reveal that the sediments are sandy loess and the environmentally sensitive fractions are

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

a ring width based reconstruction of june july minimum temperatures since ad 1245 from white spruce stands in the mackenzie delta region northwestern canada abstract we present a reconstruction of june july minimum temperatures since ad 1245 for the mackenzie delta region based on a 29 site network of white spruce picea glauca ring width series most but not all trees experienced a divergent temperature growth response similar to the divergence that has affected other white spruce trees across yukon and alaska however divergence in the study region began as early as ad 1900 and we have documented our methods to avoid including divergent signals in the reconstruction calibration verification testing based on local temperature data and multi century coherence with nearby and large scale temperature proxy records confirm that our reconstruction is robust the reconstruction shows cool conditions in the late 13th early 18th and early 19th centuries corresponding with solar minima and increased volcanism these cool periods are interrupted by warm periods consistent with early to mid 20th century warmth the late 20th century is the warmest interval and the last decade is estimated to be 1 4 c warmer than any decade before the mid 20th century the reconstructed climate history corroborates other proxy based inferences and supports the notion that high latitude regions such as the mackenzie delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries

a lacustrine record of east asian summer monsoon and atmospheric dust loading since the last interglaciation from lake xingkai northeast china a 336 cm long sediment core spanning the last 130 ka was recovered from lake xingkai on the northeastern margin of the east asian summer monsoon domain to reveal the linkage between lacustrine depositional processes and environmental changes bayesian end member modeling analysis was conducted to partition and interpret the grain size distributions of lake xingkai sediments our results suggest that the sedimentary system is characterized by three end members ems em1 and em2 with a modal value of 13 and 10 m respectively indicate the variation of local hydraulic conditions em3 with a modal value of 5 m reflects the background atmospheric dust loading high atmospheric dust concentration generally occurred during marine isotope stage mis 5d mis 4 and early mis 3 when the climate in the asian dust source region was cold and dry in contrast low dust concentration prevailed during mis 2 likely due to the southward shift of the westerlies driven by maximum ice volume in the high latitudes

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

bimodal grain size distribution of aeolian quartz in a maar of cheju island korea during the last 6500 years its flux variation and controlling factor 1 aeolian quartz chemically isolated from maar sediments in cheju island korea showed bimodal grain size distributions after partitioning into fine and coarse components fine and coarse quartz fluxes fqf and cqf were calculated the average median grain size of fine quartz was 3 m and the average fqf was 0 5 mg cm2 yr with a range of 0 1 1 6 mg cm2 yr during the last 6500 years the average cqf was 3 mg cm2 yr with a range of 1 5 5 mg cm2 yr and its average median grain size was 15 m comparisons of our results with the present aeolian dust activities and climate changes in dust source areas suggest that fqf was influenced by the pathway of the westerlies between taklimakan desert and cheju island while cqf was affected by the aridity in the source regions including the gobi desert in southern mongolia and the adjoining gobi and sand deserts in china during the last 6500 years

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

crustal structure of the grenville province in southeastern labrador from refraction seismic data evidence for a high velocity lower crustal wedge the crustal structure of the eastern grenville and makkovik provinces was determined using two onshore offshore refraction seismic lines of the lithoprobe eastern canadian shield onshore offshore transect ecsoot a gravity high in the hawke river terrane correlates with increased p wave velocities in the upper 30 km of the crust 6 2 6 7 km s in the upper and middle crust and 6 9 7 1 km s below which we interpret as structure inherited from the labradorian orogen velocities in the adjacent groswater bay terrane are 6 0 6 55 km s in the upper and middle crust and 6 6 6 95 km s in the lower crust the entire grenville crust is underlain by a 15 20 km thick high velocity lower crustal hvlc wedge consisting of an upper layer 7 1 7 4 km s and a lower layer 7 6 7 8 km s the hvlc wedge is interpreted as an underplated layer formed during iapetan rifting this interpretation is based on the correlation with the 615 ma long range dykes onshore and the eastward termination of the wedge at the cartwright

reconstruction of early spring temperature for central japan from the tree ring widths of hinoki cypress and its verification by other proxy records 1 we describe the results of a dendroclimatic study in central japan using ring width data from living trees of hinoki cypress february april temperatures were reconstructed for the period ad 1719 1961 this reconstruction from which five cooling events were determined for the late little ice age was validated against other climate proxies there is a reasonable agreement with cold periods previously estimated from documentary records in japan and china a notably good agreement is also found for a dendroclimatic reconstruction for korea suggesting that the annual activity of the winter monsoon in the western pacific rim persisted longer in the 19th century than at present records of prolonged famines and unusual climatic phenomena support the reconstruction of the cold periods in the 1780s 1810s and 1830s it is thus revealed that the hinoki chronology has enough potential to reconstruct the climatic variability further into the past

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

secular temperature trends for the southern rocky mountains over the last five centuries 1 pre instrumental surface temperature variability in the southwestern united states has traditionally been reconstructed using variations in the annual ring widths of high altitude trees that live near a growth limiting isotherm a number of studies have suggested that the response of some trees to temperature variations is non stationary warranting the development of alternative approaches towards reconstructing past regional temperature variability here we present a five century temperature reconstruction for a highaltitude site in the rocky mountains derived from the oxygen isotopic composition of cellulose d 18 oc from bristlecone pine trees the record is independent of the co located growth based reconstruction while providing the same temporal resolution and absolute age constraints the empirical correlation between d 18 oc and instrumental temperatures is used to produce a temperature transfer function a forward model for cellulose isotope variations driven by meteorological data and output from an isotope enabled general circulation model is used to evaluate the processes that propagate the temperature signal to the proxy the cellulose record documents persistent multidecadal variations in d 18 oc that are attributable to temperature shifts on the order of 1c but no sustained monotonic rise in temperature or a step like increase since the late 19th century the isotope based temperature history is consistent with both regional wood density based temperature estimates and some sparse early instrumental records citation berkelhammer m and l d stott 2012 secular temperature trends for the southern rocky mountains over the last five centuries geophys res lett 39 l17701 doi 10 1029 2012gl052447

mineralogy of aeolian dust reaching the north pacific ocean 1 sampling and analysis the mineral composition of the 2 m clay and 2 to 20 m silt size fractions of aerosol particles collected near the margins of the north pacific ocean was determined by x ray diffraction analysis although the same mineral phases are present in the two size fractions there are significant differences in the quartz plagioclase and kaolinite concentrations north pacific aerosols are primarily composed of illite in both size fractions in addition to kaolinite in the 2 m size class and quartz and plagioclase in the 2 to 20 m size class quartz and plagioclase are present in significantly higher amounts in the 2 to 20 m size fraction while kaolinite is greater in the 2 size class western north pacific aerosol particles contain significantly higher 2 m quartz than samples collected in the east and eastern north pacific aerosols have significantly higher concentrations of 2 m smectite than those from the west

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

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

asian dust transport during the last century recorded in lake suigetsu sediments asian dust has a significant impact on the natural environment its variability on multiple timescales modulates the ocean biogeochemistry and climate we demonstrate that temporal changes in the deposition flux of aeolian dust recorded in sediments from lake suigetsu central japan during the last century exhibit a continuous decreasing trend and a decadal scale decrease in 1952 1974 the former decreasing trend can be explained by a decrease in the dust storm frequency at source regions due to the warming of mongolia in the twentieth century suggesting future decrease of asian dust transport with further warming in mongolia decadal scale decrease of aeolian dust is explained by weaker westerlies in lower latitudes in central japan reflecting a weaker aleutian low during the corresponding period decadal scale westerly change probably causes north south shifts of the dominant dust transport path which affects subarctic northern pacific ocean biogeochemistry by changing the micronutrient iron supply

late pleistocene vegetation change in korea and its possible link to east asian monsoon and dansgaard oeschger d o cycles abstract late pleistocene carbon isotope 13c records from a paleolithic sedimentary sequence collected from baeki hongcheon central korea show long term changes with superimposed short term isotopic excursions the 13c value of the sedimentary organic matter a proxy for past vegetation change varied from 26 to 23 for the period between 30 and 90 ka with a long term variation similar to insolation changes high amplitude 1 to approximately 1 5 fluctuations superimposed on the long term changes in the 13c values decreased during stronger summer monsoon intervals but increased during the weakened summer monsoon this millennial scale pattern is generally similar to greenland dansgaard oeschger d o cycles the possible connection between the hongcheon area korea and high latitudes may be explained by atmospheric circulation changing in response to the d o oscillations in the northern hemisphere

late pleistocene and holocene aeolian dust deposition in north china and the northwest pacific ocean abstract rates of dust deposition in the north pacific and the central loess plateau of china show a poor correlation during the last 30 000 yr although in both cases the dust was derived from deserts in northern china loess accumulation rates were high at the time of the last glacial maximum while dust flux to the north pacific was low at this time maximum dust flux to the north pacific is recorded in the mid holocene but holocene rates of loess accumulation have been low these differences are shown to reflect the different nature of the wind conditions responsible for dust transport to the loess plateau and the north pacific dust transport responsible for formation of the loess occurred mainly in the lower 1 5 km of the atmosphere and was accomplished by cold low level northwesterly winds associated with cold waves emanating from the mongolian anticyclone at present such conditions occur quite frequently in winter but during the coldest phases of the pleistocene they probably also occurred in the spring and summer long range dust transport from northern china to the north pacific requires that the dust is lifted to high levels above 3 km where it can be incorporated into the strong mid latitude westerlies strong vertical motions of the atmosphere occur most frequently in the spring when the mongolian anticyclone begins to weaken and frontal depressions move across the deserts of northern china such frontal depressions were probably more frequent during the climatic optimum of the mid holocene and during previous interglacials changes in continental aridity have probably played a minor role in controlling the magnitude of the dust flux to the north pacific

temperature sensitive tien shan tree ring chronologies show multi centennial growth trends two millennia length juniper ring width chronologies processed to preserve multi centennial growth trends are presented for the alai range of the western tien shan in kirghizia the chronologies average the information from seven near timberline sampling sites and likely reflect summer temperature variation for comparison chronologies are also built using standard dendrochronological techniques we briefly discuss some qualities of these inter decadal records and show the low frequency components removed by the standardization process include a long term negative trend in the first half of the last millennium and a long term positive trend since about ad 1800 the multi centennial scale alai range chronologies where these trends are retained are both systematically biased but in an opposite sense in their low frequency domains nevertheless they represent the best constraints and estimates of long term summer temperature variation and reflect the medieval warm period the little ice age and a period of warming since about the middle of the nineteenth century

grain size partitioning in loess paleosol sequence on the west coast of south korea using the weibull function abstract this study aims to partition the grain size of the loess paleosol sequence on the west coast of south korea and investigates the limitations and applicability with the partitioning method through the help of a laser diffraction grain size analyzer two to four components depending on the samples and theories employed to convert the laser diffraction data to grain size data are identified through the partitioning process however the identification of one component is thought to be contingent upon the theories employed rather than natural processes the partitioning results reveal that the sequence consists mostly of fine and coarse components transported by the same mechanisms as in the chinese loess plateau and shares common source areas with the chinese loess plateau the sequence also contains a small quantity of material from the local sources and this component is expected to provide crucial information about paleoclimatic variations in korea this study suggests that considerations of the theories are essential in modeling processes of grain size because the theories greatly influence the results of grain size analysis and the number of components and that conversions using the fraunhofer approximation seem to provide more reliable results than those using the mie theory

last glacial aeolian landforms and deposits in the rhone valley se france spatial distribution and grain size characterization abstract in the rhone valley a north south oriented cenozoic rift in southeast france thick pleistocene loess deposits have been recognized since the beginning of the last century these loess records which are disconnected from the north european loess belt nelb are of significant interest to document the evolution of perimediterranean landscapes and environments during the last glacial to overcome the poor precision of available aeolian distribution maps aeolian deposits were mapped using the topsoil textural database provided by the land use and cover area frame statistical survey project lucas the grain size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops then the areas showing a similar grain size composition were extracted from the lucas rasters the resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess in better agreement with the known distribution of outcrops the map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits the deflation related landforms i e yardangs closed depressions pans and desert pavements are widespread south of narrowings of the rhone valley between latitudes 44 n and 45 n they indicate palaeowinds blowing from the north northwest aeolian sand loessic sand sandy loess and loess deposits successively spread on both sides of the rhone river the loess is characterized by a coarse texture main mode around 60 m strong local thickness 5 m limited extension and abundant bioturbation this preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the last glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources

the eolian origin of silty mantle in sedentary soils from korea and japan abstract the concentration particle size distribution and oxygen isotope composition 18 o smow of quartz were examined in order to determine the extent to which the accretion of long distance eolian dusts from the interior of china had formed the sedentary soils overlying diverse parent materials in korea and japan the quartz content of the surface soils developed on quartz free basaltic materials varies from 8 9 to 47 7 generally the soil quartz found in surface horizons is finer than of the subsurface horizons and or substrata the particle size of the soil quartz decreases from the west coast to eastern coastal margins of korea and to the japanese islands this follows the major trajectory of westerly winds which carry the eolian dusts from the interior of china to mid latitude regions of the north pacific the oxygen isotope composition of the fine quartz 1 10 m in diameter when separated from surface and subsurface horizons is found in a relatively narrow range of 15 9 to 17 7 the values are indiscernible from those of recent eolian dusts from the interior desert and loess plateau of china the 18 o values from the same sized quartz found in c horizons 10 4 and 19 2 consisting of saprolitic andesites and shales respectively differ from those of the overlying soils the 18 o values of soil quartz developed on igneous materials systematically decrease with increasing particle size to 53 m 14 they abruptly decrease to 8 to 12 for fractions larger than 53 m a large apparent oxygen isotope fractionation up to 10 between fine 17 and coarse 8 to 12 grained quartz observed in the samples does not represent an equilibrium oxygen isotope fractionation for normal magmatic processes the data provide evidence for an eolian origin of the fine quartz incorporated during soil development

ordovician rocks in the eastcan et al freydis b 87 and other wells in offshore atlantic canada acritarchs and chitinozoa from the lower 1300 ft 400 m of the eastcan et al freydis b 87 well labrador shelf indicate that these strata accumulated in a marine setting during late ordovician t

eolian quartz flux variations in cheju island korea during the last 6500 yr and a possible sun monsoon linkage we have obtained a high resolution sedimentary record covering the last 6500 yr from a maar in cheju island korea in order to reconstruct the history of variations in the eolian quartz flux eqf and hence asian dust the long term variation of eqf reveals three intervals a period of high eqf 4000 2000 cal yr b p and two periods of low eqf 6500 4000 cal yr b p and 2000 cal yr b p to present which have been affected by the east asian monsoon due to insolation change and the cold air activity in high latitudes correlated with polar high pressure systems this long term variation is superimposed by millennial and centennial scale fluctuations with periodicities of 1137 739 214 162 137 127 and 111 yr implying drier conditions in the source areas in china the detrended eqf record correlates visually and statistically cross spectral analysis with the atmospheric d 14 c record solar proxy the centennial scale variability in eqf may be affected

effect of scaling and regression on reconstructed temperature amplitude for the past millennium 1 examination of large scale millennial long temperature reconstructions reveals a wide range of datasets and methods used for calibration proxy time series are commonly calibrated against overlapping instrumental records representing different seasons northern hemisphere latitudinal bands and including or excluding sea surface temperature data methodological differences include using scaling or regression the calibration time period and smoothing data before calibration we find that these various approaches alone can result in differences in the reconstructed temperature amplitude of about 0 5 c this magnitude is equivalent to the mean annual temperature change for the northern hemisphere reported in the last ipcc report for the 1000 1998 period a more precise assessment of absolute reconstructed temperature amplitudes is necessary to help quantify the relative influences of forcing mechanisms in climate models

palaeoenvironmental reconstruction of kathu pan south africa based on sedimentological data abstract several studies have highlighted the importance of collecting well dated records of palaeoenvironmental changes on desert margins particularly in the semi arid interior of southern africa here we describe sediments at three sites in kathu pan a pan complex overlying karstic bedrock at the southern edge of the kalahari basin sinkholes have exposed sedimentary sequences dating back to the pleistocene making it possible to document multiple palaeoenvironmental regimes in this landscape using a multi analytical sedimentological approach including micromorphology energy dispersive x ray spectrometry electron microprobe loss on ignition laser diffractometry and luminescence dating we demonstrate that the sediments at kathu pan represent an environment fluctuating among a number of thresholds for accumulation of different kinds of transported and authigenic sediments within the pleistocene sands at the base of our studied sedimentary sequence the presence of palygorskite indicative of less extreme evaporative control represents a semi arid environment from 156 11 ka to 32 2 ka marine isotope stages 6 3 increased moisture availability at 84 4 ka and at 96 5 ka possibly during marine isotope stages 5a and 5c respectively is reflected in the sands by the formation of palygorskite in concert with the deposition and oxidation of organic material as the climate became increasingly arid possibly in response to global cooling during the last glacial maximum 21 2 ka kathu pan crossed a threshold and deposition of caco3 dominated over that of palygorskite in the holocene beds within our studied unit alternating caco3 and organic dominated deposits sometimes in very fine laminae reflect an increase in the amplitude of either seasonal or annual changes in water availability

enso like modulated tropical pacific climate changes since 2 36 myr and its implication for the middle pleistocene transition el nino southern oscillation enso activity and the pacific walker circulation are controlled by the zonal sea surface temperature sst gradient between the western and eastern equatorial pacific eep and the corresponding barometric difference variations in the zonal sst gradient since the early pleistocene have primarily been triggered by changes in the sst in the eastern equatorial pacific however the response of the enso like long term state to the cooling of the eep and its coupling role with tropical pacific climate changes are still not well established here we present a high resolution grain size record spanning the last 2 36 myr obtained from marine core sediment located in the west philippine sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism by combining our data with other long term climatic records from the equatorial pacific we demonstrate that the cooling of sst and enhanced upwelling in the eep resulted in the development of the walker circulation and increased monsoon precipitation in luzon from 2 2 to 1 6 myr from 1 2 to 0 8 myr and since 0 2 myr ago the progressive cooling of the high latitudes in the quaternary may be responsible for our observation here a newly identified 100 kyr dominant period between 2 2 and 1 6 myr in the enso like modulated pacific climate records indicates that the enso like system may play a key role in facilitating or responding to the global climate changes

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

a 1052 year tree ring proxy for alpine summer temperatures a june august alpine temperature proxy series is developed back to ad 951 using 1 527 ring width measurements from living trees and relict wood the reconstruction is composed of larch data from four alpine valleys in switzerland and pine data from the western austrian alps these regions are situated in high elevation alpine environments where a spatially homogenous summer temperature signal exists in an attempt to capture the full frequency range of summer temperatures over the past millennium from inter annual to multi centennial scales the regional curve standardization technique is applied to the ring width measurements correlations of 0 65 and 0 86 after decadal smoothing with high elevation meteorological stations since 1864 indicate an optimal response of the rcs chronology to june august mean temperatures the proxy record reveals warm conditions from before ad 1000 into the thirteenth century followed by a prolonged cool period reaching minimum values in the 1820s and a warming trend into the twentieth century this latter trend and the higher frequency variations compare well with the actual high elevation temperature record the new central alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium it also reveals significant similarities at inter decadal to multi centennial frequencies with large scale temperature reconstructions however deviating during certain periods from h h lamb s european north atlantic temperature history

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

long term temperature trends and tree growth in the taymir region of northern siberia abstract the northernmost conifers in the world are located well above the arctic circle in the taymir region of northern siberia and have been recording the thermal environment for centuries to millennia the trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth photosynthesis lignification of cell walls and other biochemical processes data from annual tree ring widths are used to reconstruct may september mean temperatures for the past four centuries these warm season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century however there is a loss of thermal response in ring widths since about 1970 previously the warmer temperatures induced wider rings most major warming and cooling trends are in agreement with other high latitude temperature reconstructions based on tree ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century

boreal temperature variability inferred from maximum latewood density and tree ring width data wrangell mountain region alaska abstract variations in both width and density of annual rings from a network of tree chronologies were used to develop high resolution proxies to extend the climate record in the wrangell mountain region of alaska we developed a warm season july september temperature reconstruction that spans a d 1593 1992 based on the first eigenvector from principal component analysis of six maximum latewood density mxd chronologies the climate tree growth model accounts for 51 of the temperature variance from 1958 to 1992 and shows cold in the late 1600s early 1700s followed by a warmer period cooling in the late 1700s early 1800s and warming in the 20th century the 20th century is the warmest of the past four centuries several severely cold warm seasons coincide with major volcanic eruptions the first eigenvector from a ring width rw network based on nine chronologies from the wrangell mountain region a d 1550 1970 is correlated positively with both reconstructed and recorded northern hemisphere temperatures rw shows a temporal history similar to that of mxd by increased growth warmer and decreased growth cooler intervals and trends after around 1970 the rw series show a decrease in growth while station data show continued warming which may be related to increasing moisture stress or other factors both the temperature history based on mxd and the growth trends from the rw series are consistent with well dated glacier fluctuations in the wrangell mountains and some of the temperature variations also correspond to variations in solar activity

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

dendroclimatic reconstruction of summer temperatures in northwestern canada since a d 1638 based on age dependent modeling abstract ring widths from five picea glauca stands at the alpine treeline in northwestern canada are used to investigate climate growth responses and to develop a long reconstruction of summer temperatures response function and linear regression analyses indicate that the radial growth response of these trees to climate varies with age and site at most sites the period of significant positive response to growing season temperatures declines with tree age age dependent and standard age independent models are then used to develop two reconstructions of june july temperatures for northwestern canada extending back to a d 1638 calibration statistics were similar for both models but the standard model performed poorly during verification the reconstruction produced using age dependent modeling suggests june july temperatures were cooler than present throughout most of the past 350 years with the exception of the late 18th century particularly cool periods occurred at 1700 and in the mid 19th century in constast the standard model suggests that temperatures were similar to or warmer than present during the last 350 years the age dependent reconstruction compares favorably with other proxy climate records from northern north america age dependent dendroclimatic modeling can provide a sensitive record of recent climatic change that allows the inclusion of previously rejected sites into dendroclimatic analyses

a matter of divergence tracking recent warming at hemispheric scales using tree ring data 1 no current tree ring tr based reconstruction of extratropical northern hemisphere enh temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record over recent decades a divergence between cooler reconstructed and warmer instrumental large scale temperatures is observed we hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period in this study we compiled tr data and published local regional reconstructions that show no divergence against local temperatures these data have not been included in other large scale temperature reconstructions utilizing this data set we developed a new completely independent reconstruction of enh annual temperatures 1750 2000 this record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that tr data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale although the new series tracks the increase in enh annual temperatures over the last few decades better than any existing reconstruction it still slightly under predicts values in the post 1988 period we finally discuss possible reasons why it is so difficult to model post mid 1980s warming provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large scale reconstruction attempts that may result in more robust temperature estimates