a late glacial high resolution site and source temperature record derived from the epica dome c isotope records east antarctica the timing and synchronisation of greenland and antarctic climate events that occurred during the last glacial period are still under debate as is the magnitude of temperature change associated with these events here we present detailed records of local and moisture source temperature changes spanning the period 27 45 kyr bp from water stable isotope measurements deltad and delta 18 o in the recently drilled epica dome c ice core east antarctic plateau using a simple isotopic model site deltat site and source deltat source temperatures are extracted from the initial 50 yr high resolution isotopic records taking into account the changes in seawater isotopic composition the deuterium isotope variability is very similar to the less precise deltad record from the vostok ice core and the site temperature inversion leads to a temperature profile similar to the classical palaeothermometry method due to compensations between source and ocean water corrections the reconstructed deltat site and deltat source profiles show different trends during the glacial the former shows a decreasing trend from the warm al event 38 kyr bp toward the last glacial maximum while the latter shows increasing values from 41 to 28 kyr bp the low frequency deuterium excess fluctuations are strongly influenced by obliquity fluctuations controlling the low to high latitude temperature gradients and show a remarkable similarity with a high resolution southeast atlantic sea surface temperature record a comparison of the temperature profiles site and source and temperature gradient deltat source deltat site with the non sea salt calcium and sodium records suggests a secondary influence of atmospheric transport changes on aerosol variations

rates of late quaternary normal faulting in central tibet from u series dating of pedogenic carbonate in displaced fluvial gravel deposits along the main boundary fault of the central tibetan shuang hu graben two well preserved fluvial terrace surfaces are vertically offset by 1 3 m terrace i and 14 8 m terrace ii using thermal ionization mass spectrometry tims we have determined 48 230th 234u 238u ages of small 10 40 mg samples from pedogenic carbonate rinds on clasts in the terrace deposits based on textural microstratigraphic and geochemical criteria we conclude that the u series ages of innermost rind samples provide reliable ages of 16 4 1 9 ka for terrace i and 233 1 9 3 ka for terrace ii this constrains the average rate of vertical displacement along the normal fault to be 0 079 0 011 mm yr during the past 16 kyr and 0 064 0 007 mm yr during the past 233 kyr combining these results with slip rate estimates for other normal faults along the graben margins indicates that the cumulative vertical displacement on all normal faults did not exceed 0 3 mm yr during the late quaternary this new rate from central tibet is distinctly lower than the rate of 1 9 0 6 mm yr inferred for normal faults bounding the yadong gulu graben system in southern tibet consistent with more pronounced and common graben development in southern tibet we therefore suggest that normal faulting in southern tibet is largely controlled by local processes and that the age of its initiation is not a valid proxy for uplift of the tibetan plateau as has been widely assumed our data also place chronologic constraints on the termination of periglacial conditions in central tibet during the last three interglaciations rind formation appears to have been relatively continuous on clasts in terrace i from 16 ka clast rinds from terrace ii in contrast are characterized by three main episodes of rind growth that are widely separated in time the earliest and least well preserved episode started at 233 1 9 3 ka a second episode occurred at 131 8 7 8 ka and a third episode was approximately coeval with rind formation in terrace i after 16 4 1 9 ka in each case the age of onset of carbonate rind accumulation coincides with independently estimated ages of global deglaciation accordingly we conclude that periglacial conditions in the central tibetan plateau terminated synchronously with early stages of global warming following the last three glacial maxima and that fluvial aggradation terrace formation and pedogenic carbonate accumulation in terrace soils ensued rapidly

evidence for warmer interglacials in east antarctic ice cores reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotopic ratios and temperature are stable in space and time sime et al analyse three 340 000 year old ice cores from east antarctica and use an isotope enabled general circulation model to show that instead the relationship is nonlinear during warm periods the ratios are less sensitive to temperature so previous estimates of interglacial temperatures are likely to be about 3 c too low this is consistent with peak antarctic interglacial temperatures at least 6 c higher than today this work suggests that there are serious deficiencies in our understanding of climates that are warmer than today s reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time three east antarctic ice core records are now analysed alongside input from general circulation models to reveal that during warmer interglacial periods the isotope ratios are less sensitive to temperature than during colder interglacials consequently previous estimates of interglacial temperatures are probably too cold stable isotope ratios of oxygen and hydrogen in the antarctic ice core record have revolutionized our understanding of pleistocene climate variations and have allowed reconstructions of antarctic temperature over the past 800 000 years 800 kyr refs 1 2 the relationship between the d h ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform 10 over east antarctica3 and constant with time 20 refs 3 5 in the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores prior general circulation model gcm studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3 5 here we analyse the three available 340 kyr east antarctic ice core records alongside input from gcm modelling we show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites and that therefore the conversions must be nonlinear for at least some sites model results indicate that the isotopic composition of east antarctic ice is less sensitive to temperature changes during warmer climates we conclude that previous temperature estimates from interglacial climates are likely to be too low the available evidence is consistent with a peak antarctic interglacial temperature that was at least 6 k higher than that of the present day approximately double the widely quoted 3 1 5 k refs 5 6

distribution of stable isotopes in surface snow along the route of the 1990 international trans antarctica expedition this paper presents the distri bution of average od and 6180 values for the top i m of surface snow for a large area of antarctica the samples were collected on the 1990 internatio nal trans antarctica expedition which crossed the continent from the northern tip of the antarctic penins ula to mirny station the empirical rel ationships between the isotopes temperature and elevation are computed the slopes of od with respect to the surface temperature for the segments west patriot hills v ostok and east ofvostok komso molskaya mirny are not signifi cantly different to that obse rved between dumont d urville and dome c lorius and merlivat 1977 which are often used to inte rpret deep ice core isotopic profiles there is however a noti ceable shift between the two regression lines

linear and non linear response of late neogene glacial cycles to obliquity forcing and implications for the milankovitch theory constraints are given for the geometry and time lags of the prominent obliquity paced glacial stages 100 98 and 96 which mark a major phase in northern hemisphere nh glaciations during the late pliocene 2 56 2 4 ma ago for this purpose a high resolution benthic 18o record was constructed from the astronomically tuned mediterranean odp site 967 and decomposed into an ice volume and an annual nh 40 80 n temperature component using an inverse modelling approach our results indicate that the dominant 41 ky component in 18o lags obliquity by 6 5 0 6 ky which approximates late pleistocene estimates maximum minimum ice volume growth occurred in phase with obliquity minima maxima which invoked low high total summer energy conditions that reduced increased ice sheet ablation sea level dropped 60 70 m during full glacial conditions similar to late pleistocene ice core and marine 18o records our late pliocene 18o record reveals significant power at 28 ky which appear to be bound to the major glacial terminations we argue that this beat most likely reflects the sum frequency of the 41 ky prime and its multiples of 82 and 123 ky supporting the theory that the late neogene glacial cycles are primarily determined by the linear and non linear response mechanisms of the ice sheets to the obliquity forcing evidence for such a scenario may come from the alignment between the devils hole 18o chronology and the sum of the filtered linear and non linear obliquity related components of late pleistocene climate records suggesting that the 28 ky beat is intrinsic to the climate system or at least an important constituent of the annual high latitude nh temperature changes that have set the stage for the geometry of the glacial interglacial variability throughout the course of the pliocene and pleistocene

short fluctuations in antarctic isotope records a link with cold events in the north atlantic abstract the recent synchronization of antarctic and greenland ice cores obtained by blunier and colleagues from methane measurements in the 10 15 kyr and 25 45 kyr intervals allows us to investigate leads and lags between climatic changes in the two hemispheres we observe that most of the cold episodes recorded in the greenland ice correspond to peaks in isotope antarctic records once the common timescale derived from methane measurements is adopted these antarctic peaks are commonly interpreted as reflecting warmings in antarctica here we draw attention on a possible alternative explanation those peaks could at least partially correspond to a temporary cooling of the source water providing antarctic precipitation as a result of cold conditions in the north atlantic and of a fast interhemispheric transfer of this cooling via the atmosphere or the ocean this suggestion would be consistent with recent measurements of the deuterium excess in vostok ice antarctica although there are good arguments in favor of the currently accepted interpretation the influence of temperature changes in the source regions of antarctic precipitation on the temperature proxy has to be kept in mind when interpreting the phasing between greenland and antarctic ice core records

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

understanding the 17o excess glacial interglacial variations in vostok precipitation combined measurements of delta o 18 delta o 17 and delta d in ice cores leading to d excess and o 17 excess are expected to provide new constraints on the water cycle and past climates we explore different processes both in the source regions and during the poleward transport that could explain the o 17 excess increase by 20 per meg observed from the last glacial maximum lgm to early holocene eh at the vostok station using a single column model over tropical and subtropical oceans we show that the relative humidity at the surface is the main factor controlling o 17 excess in source regions then using a rayleigh type model we show that the o 17 excess signal from the source region is preserved in the polar snowfall contrary to d excess evaporative recharge over mid and high latitudes and delta o 18 seasonality in polar regions can also affect the vostok o 17 excess but cannot account for most of the 20 per meg deglacial increase from lgm to eh on the other hand a decrease of the relative humidity at the surface rh s by 8 to 22 would explain the observed change in o 17 excess such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity if the surface thermodynamic disequilibrium decreased by 4 degrees c such a change in rh s would affect source and polar temperatures reconstructions from delta o 18 and d excess measurements strengthening the interest of o 17 excess measurements to better constrain such changes

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

the last five glacial interglacial transitions a high resolution 450 000 year record from the subantarctic atlantic 1 a submillennial resolution radiolarian based record of summer sea surface temperature sst documents the last five glacial to interglacial transitions at the subtropical front southern atlantic ocean rapid fluctuations occur both during glacial and interglacial intervals and sudden cooling episodes at glacial terminations are recurrent surface hydrography and global ice volume proxies from the same core suggest that summer sst increases prior to terminations lead global ice volume decreases by 4 7 3 7 ka in the eccentricity band 6 9 2 5 ka obliquity and 2 7 0 9 ka precession a comparison between sst and benthic 13c suggests a decoupling in the response of northern subantarctic surface intermediate and deep water masses to cold events in the north atlantic the matching features between our sst record and the one from core md97 2120 southwest pacific suggests that the super regional expression of climatic events is substantially affected by a single climatic agent the subtropical front amplifier and vehicle for the transfer of climatic change the direct correlation between warmer tsite at vostok and warmer sst at odp site 1089 suggests that warmer oceanic atmospheric conditions imply a more southward placed frontal system weaker gradients and therefore stronger agulhas input to the atlantic ocean

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

southern ocean upwelling earth s obliquity and glacial interglacial atmospheric co2 change previous studies have suggested that during the late pleistocene ice ages surface deep exchange was somehow weakened in the southern ocean s antarctic zone which reduced the leakage of deeply sequestered carbon dioxide and thus contributed to the lower atmospheric carbon dioxide levels of the ice ages here high resolution diatom bound nitrogen isotope measurements from the indian sector of the antarctic zone reveal three modes of change in southern westerly wind driven upwelling each affecting atmospheric carbon dioxide two modes related to global climate and the bipolar seesaw have been proposed previously the third mode which arises from the meridional temperature gradient as affected by earth s obliquity axial tilt can explain the lag of atmospheric carbon dioxide behind climate during glacial inception and deglaciation this obliquity induced lag in turn makes carbon dioxide a delayed climate amplifier in the late pleistocene glacial cycles

epica dome c record of glacial and interglacial intensities abstract climate models show strong links between antarctic and global temperature both in future and in glacial climate simulations past antarctic temperatures can be estimated from measurements of water stable isotopes along the epica dome c ice core over the past 800 000 years here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile the consistency between stable isotope derived temperature and other environmental and climatic proxies measured along the edc ice core is analysed at the orbital scale and compared with estimates of global ice volume mis 2 12 and 16 appear as the strongest glacial maxima while mis 5 5 and 11 appear as the warmest interglacial maxima the links between edc temperature global temperature local and global radiative forcings are analysed we show i a strong but changing link between edc temperature and greenhouse gas global radiative forcing in the first and second part of the record ii a large residual signature of obliquity in edc temperature with a 5 ky lag iii the exceptional character of temperature variations within interglacial periods focusing on mis 5 5 the warmest interglacial of edc record we show that orbitally forced coupled climate models only simulate a precession induced shift of the antarctic seasonal cycle of temperature while they do capture annually persistent greenland warmth models fail to capture the warming indicated by antarctic ice core d we suggest that the model data mismatch may result from the lack of feedbacks between ice sheets and climate including both local antarctic effects due to changes in ice sheet topography and global effects due to meltwater thermohaline circulation interplays an mis 5 5 sensitivity study conducted with interactive greenland melt indeed induces a slight antarctic warming we suggest that interglacial edc optima are caused by transient heat transport redistribution comparable with glacial north south seesaw abrupt climatic changes

spatial distribution of 17o excess in surface snow along a traverse from zhongshan station to dome a east antarctica the influence of temperature on the triple isotopic composition of oxygen in water is still an open question and limits the interpretation of water isotopic profiles in antarctic ice cores the main limitation arises from the lack of 17o excess measurements in surface snow and especially for remote regions characterized by low temperature and accumulation rate in this study we present new 17o excess measurements of surface snow along an east antarctic traverse from the coastal zhongshan station to the highest point of the antarctic ice sheet at dome a the 17o excess data significantly decrease inland with a latitudinal gradient of 1 33 0 41 per meg degree an altitudinal gradient of view the mathml source and a temperature gradient of view the mathml source theoretical calculations performed using a rayleigh model attribute this inland decrease to kinetic isotopic fractionation occurring during condensation from vapor to ice under supersaturation conditions at low temperatures however large heterogeneity of 17o excess in antarctic precipitation cannot only be explained by temperature at condensation and or influences of relative humidity in the moisture source region

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

a 420 000 year deuterium excess record from east antarctica information on past changes in the origin of precipitation at vostok here we present and analyze the complete vostok ice cores deuterium excess record which spans the last four climatic cycles back to 420 000 years b p to extract paleoclimate information from this record we use isotopic modeling showing that changes in deuterium excess d d 8 18o of vostok precipitation reflect changes in the average temperature of oceanic moisture sources over the last 250 000 years the deuterium excess is strongly anticorrelated with changes in earth s obliquity this reflects changes in the relative contribution of low and high latitudes to the vostok precipitation resulting from changes in the latitudinal annual mean insolation gradient governed by the obliquity however this modulation by obliquity is not observed prior to 250 000 years b p we attribute this difference to the ice flow the deeper ice under vostok station having accumulated in a location upstream vostok receiving precipitation from different oceanic origins despite this difference between the earlier and the later portions of the record the deuterium excess changes during all the glacial inceptions are similar in amplitude and timing relative to the deuterium decrease the glacial inceptions are characterized by high deuterium excess indicating the significant role of the tropics in supplying moisture to the already cold poles

optimum multiparameter analysis of mixing in the thermocline of the eastern indian ocean a method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations it requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types the procedure to establish the water types find the correct weights for the parameters and solve the mixing equations through minimization of the residuals is described in detail the method is applied to a data set from the eastern indian ocean where indian central water and australasian mediterranean water meet to produce a strong front in the thermocline it is shown that although most of the water from the indonesian archipelago is carried westward north of 11 s contributions from the australasian mediterranean water are found as far south as 25 s particularly along the australian shelf as a result of advection with the leeuwin current

the deep ocean during the last interglacial period oxygen isotope analysis of benthic foraminifera in deep sea cores from the atlantic and southern oceans shows that during the last interglacial period north atlantic deep water nadw was 0 4 0 2 c warmer than today whereas antarctic bottom water temperatures were unchanged model simulations show that this distribution of deep water temperatures can be explained as a response of the ocean to forcing by high latitude insolation the warming of nadw was transferred to the circumpolar deep water providing additional heat around antarctica which may have been responsible for partial melting of the west antarctic ice sheet

paleo climate of the boise area idaho from the last glacial maximum to the present based on groundwater δ2h and δ18o compositions abstract a 30 ka paleo climate record of the boise area idaho usa has been delineated using groundwater stable isotopic compositions groundwater ages are modern cold batholith 5 15 ka thermal batholith 10 20 ka frontal fault and 20 30 ka snake river plain thermal the stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation using 2h and 18o compositions local groundwater lines lgwl s were defined for each system each lgwl has been evaluated with defined slopes of 6 94 and 8 respectively and resulting deuterium excess values d were found for each groundwater system for each slope time dependent changes in moisture source humidity and temperature and boise area recharge temperatures calculated from stable isotopic data and the deuterium excess factors agree with previous paleo climate studies results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9 sea surface temperature at the moisture source increased 6 7 c and local boise temperature increased by 4 5 c a greater increase of temperature at the moisture source as compared to the boise area may impart be due to a shift in the moisture source area

quantitative estimate of the milankovitch forced contribution to observed quaternary climate change a number of records commonly described as showing control of climate change by milankovitch insolation forcing are reexamined the fraction of the record variance attributable to orbital changes never exceeds 20 in no case including a tuned core do these forcing bands explain the overall behavior of the records at zero order all records are consistent with stochastic models of varying complexity with a small superimposed milankovitch response mainly in the obliquity band evidence cited to support the hypothesis that the 100 ka glacial interglacial cycles are controlled by the quasi periodic insolation forcing is likely indistinguishable from chance given the small sample size andnear integer ratios of 100 ka to the precessional period s at the least the stochastic background noise is likely to be of importance r 2004 elsevier ltd all rights reserved

grip deuterium excess reveals rapid and orbital scale changes in greenland moisture origin the northern hemisphere hydrological cycle is a key factor coupling ice sheets ocean circulation and polar amplification of climate change here we present a northern hemisphere deuterium excess profile covering one climatic cycle constructed with the use of 18 o and d greenland ice core project grip records past changes in greenland source and site temperatures are quantified with precipitation seasonality taken into account the imprint of obliquity is evidenced in the site to source temperature gradient at orbital scale at the millennial time scale grip source temperature changes reflect southward shifts of the geographical locations of moisture sources during cold events and these rapid shifts are associated with large scale changes in atmospheric circulation

seasonally resolved diatom δ18o records from the west antarctic peninsula over the last deglaciation understanding the response of the antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st century warming a unique diatom 18o record derived from a high resolution deglacial seasonally laminated core section off the west antarctic peninsula wap is presented here by extracting and analysing single species samples from individual laminae season specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months as well as documenting significant intra annual seasonal variability during the deglaciation with increased discharge occurring in summer relative to spring further intra seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in whilst deglacial 18o are typically lower than those for the holocene indicating glacial discharge to the core site peaked at this time inter annual and inter seasonal alternations in excess of 3 suggest significant variability in the magnitude of these inputs these deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the wap as well as regional marine atmospheric interactions in constraining changes in glacial discharge over the last deglaciation the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean climate variability along the wap

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

glacial surface temperatures of the southeast atlantic ocean a detailed record of sea surface temperature from sediments of the cape basin in the subtropical south atlantic indicates a previously undocumented progression of marine climate change between 41 and 18 thousand years before the present ky b p during the last glacial period whereas marine records typically indicate a long term cooling into the last glacial maximum around 21 ky b p consistent with gradually increasing global ice volume the cape basin record documents an interval of substantial temperate ocean warming from 41 to 25 ky b p the pattern is similar to that expected in response to changes in insolation owing to variations in earth s tilt

chronology of the vostok ice core constrained by o2 n2 ratios of occluded air and its implication for the vostok climate records abstract we present a timescale for the vostok ice core that is derived by orbitally tuning to o 2 n 2 ratios in occluded air for depths deeper than 1550 m 112 ka and by gas correlation to the gisp2 chronology for the section shallower than 1422 m 2 exclusion and hence the o 2 n 2 ratio in trapped gases the newly derived o 2 n 2 chronology is consistent with absolutely dated speleothem records the o 2 n 2 chronology differs from previously published orbital tuning chronologies ch 4 and 18 o atm by up to 6 kyr and from the original gt4 chronology by up to 15 kyr the difference between the o 2 n 2 chronology and the 18 o atm chronology varies in time with strong signals centered at 1 100 and 1 41 kyr 1 the ages for the last four glacial terminations in vostok correspond to high obliquity 23 7 at terminations midpoints they also correspond with decreasing precession index corresponding to increasing boreal summer insolation the vostok temperature record boreal summer insolation and the rate of change of the specmap property reflecting planktonic foram 18 o with respect to time are highly coherent at precession and obliquity periods these three properties vary almost synchronously with the possibility that vostok temperature lags behind the other two our new timescale supports the widespread view that boreal summer insolation played an important role in glacial interglacial cycles

an observation based method for reconstructing ocean surface changes using a 340 000 year deuterium excess record from the dome fuji ice core antarctica 1 an extended deuterium excess d or d excess record covering the last three glacial interglacial cycles ca 340 000 years was obtained from the dome fuji ice core antarctica in order to interpret the antarctic d record as a climatic history of vapor source regions the record should be corrected for the antarctic site temperature effect we propose an observation based method for correcting the d record that method uses a regression curve of the observed spatial relationship between d and d in antarctica on the assumption that the present slope has not changed unlike the previously proposed model based method our correction method results in considerable change in the d profile of the dome fuji ice core the corrected d record anticorrelates with a mean ocean 18o record r2 0 74 and correlates with a sst record r2 0 58 throughout the observed period these results emphasize the significance of our empirical correction method

carbon and oxygen cycles sensitivity to changes in environmental forcing in a coastal upwelling system 1 biogeochemical cycles in the coastal ocean are changing and will continue to change in response to a changing climate effects on the oxygen and carbon cycles are particularly important as either episodic or permanent shifts toward lower oxygen and or higher inorganic carbon conditions can impact coastal ecosystems negatively here we study the sensitivity of these cycles to changes that may occur in the coastal ocean focusing on a summer wind driven upwelling region off southern vancouver island shelf we use a quasi 2 d configuration of the regional ocean modeling system roms to perform six sensitivity experiments results indicate that carbon and oxygen cycles in this region may be significantly affected by an altered upwelling season a shallower offshore oxygen minimum zone and a carbon enriched environment combinations of these scenarios suggest a potentially increasing risk for the development of coastal hypoxia and corrosive conditions in the region

oxygen in the deep strait of georgia 1951 2009 the roles of mixing deep water renewal and remineralization of organic carbon the concentration of oxygen in the deep strait of georgia has declined at a rate of 0 45 1 3 mmol l21 yr21 since 1971 and now seasonally approaches thresholds of biological tolerance the decline has resulted principally from the increasing hypoxia of upwelled pacific ocean water local anthropogenic loadings have little potential to reduce bottom water oxygen concentrations hypoxic upwelled water mixes vigorously with surface water in the tidal passages of haro strait before entering the deep strait of georgia during a series of deep water renewal events in late spring and late summer remineralization of at least 22 mmol l21 yr21 together with diffusive mixing reduces the bottom water oxygen concentration to a winter minimum of 90 110 mmol l21 linear extrapolation of the long term trend indicates that parts of the strait could become episodically hypoxic 62 5 mmol l21 1 4 ml l21 as early as 2042 however water mass modeling shows that the mixing with surface water in haro strait limits the potential of the shelf water to reduce the oxygen concentration in the deep strait even should the shelf water become completely anoxic the concentration of oxygen in bottom waters would level off just above 90 mmol l21 after 3 yr increasing surface water temperature will reduce the solubility of oxygen but this effect is projected to cause a further decline of only 2 2 mmol l21 over the next 25 yr despite its restricted circulation the deep strait of georgia is less threatened by hypoxia than are many other coastal areas because of the combination of light limited primary production and intense tidal mixing in the approaches which replenishes the deep water oxygen annually

persistently declining oxygen levels in the interior waters of the eastern subarctic pacific abstract fifty years of measurements at ocean station papa osp 50 n 145 w show trends in the interior waters of the subarctic pacific that are both impacted by short term few years to bi decadal atmospheric or ocean circulation oscillations and by persistent climate trends between 1956 and 2006 waters below the ocean mixed layer to a depth of at least 1000 m have been warming and losing oxygen on density surfaces found in the depth range 100 400 m 26 3 27 0 the ocean is warming at 0 005 0 012 c y 1 whereas oxygen is declining at 0 39 0 70 mol kg 1 y 1 or at an integrated rate of 123 mmol m 2 y 1 decrease of 22 over 50 years during this time the hypoxic boundary defined as 60 mol o 2 kg 1 has shoaled from 400 to 300 m in the alaska gyre the 26 2 isopycnal occasionally ventilates whereas at osp 26 0 has not been seen at the ocean surface since 1971 as the upper ocean continues to stratify to interpret the 50 year record at osp the isopycnal transport of oxygenated waters within the interior of the subarctic pacific is assessed by using a slightly modified no parameter broecker w 1974 no a conservative water mass tracer earth and planetary science letters 23 100 107 the highest nitrate oxygen signature in interior waters of the north pacific is found in the bering sea gyre western subarctic gyre and east kamchatka current region as a consequence of winter mixing to the 26 6 isopycnal by mixing with low no waters found in the subtropics and okhotsk sea this signature is diluted as waters flow eastward across the pacific evidence of low no waters flowing north from california is seen along the coasts of british columbia and se alaska oxygen in the subsurface waters of the alaskan gyre was supplied 60 by subarctic and 40 by subtropical waters during woce surveys whereas such estimates are shown to periodically vary by 20 at osp other features discernable in the osp data include periods of increased ventilation of deeper isopycnals on an 18 year cycle and strong short term few month variability caused by passing mesoscale eddies the potential impacts of declining oxygen on coastal ecosystems are discussed

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

a comparison of the vostok ice deuterium record and series from southern ocean core md 88 770 over the last two glacial interglacial cycles taking advantage of the fact that the vostok deuterium d record now covers almost two entire climatic cycles we have applied the orbital tuning approach to derive an age depth relation for the vostok ice core which is consistent with the specmap marine time scale a second age depth relation for vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from southern ocean core md 88 770 both methods lead to a close correspondence between vostok and md 88 770 time series however the coherence between the correlated d and insolation is much lower than between the orbitally tuned 8d and insolation this reflects the lower accuracy of the correlation method with respect to direct orbital tuning we compared the ice and marine records set in a common temporal framework in the time and frequency domains our results indicate that changes in the antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands moreover the average phase we estimated between the filtered d and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes the relatively large lag found between vostok d variations and obliquity driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies finally in contrast to the cross spectral analysis method used in previous studies the method we use here to estimate the phases can reveal errors in cross correlations with orbitally tuned chronologies

inferences from stable water isotopes on the holocene evolution of scharffenbergbotnen blue ice area east antarctica we show that it is possible to extract a high resolution annual paleoclimate record from the surface of a blue ice area bia the variability of the surface stable isotope values suggests that almost all the surface ice in scharffenbergbotnen bia east antarctica is of holocene age the isotopic changes across the bia show that the modern climate there is warmer than the climate in the early holocene optimum 11 kyr bp a volume conserving ice flow model for the bia constrained by isotopic variability and layer thicknesses and a series of 14 c ages indicate both that the bia has been smaller than now and that the surface velocities were considerably smaller during the last glacial maximum changes in ice sheet thickness drive the bia towards present day conditions the relatively young age of the majority of the bia also explains the lack of meteorite finds in this area and may be typical for many bias in low elevation nunatak areas

the grip deuterium excess record abstract ice cores from greenland and antarctica are ideal archives for retrieving long time series of deuterium excess d d 8 18 o a parameter influenced by conditions prevailing in the oceanic regions which provide moisture for polar snow the central greenland grip deuterium excess record has recently been interpreted in terms of oceanic source temperatures both for the holocene and for the last glacial period this approach being less straightforward for the latter period because of changes in the precipitation seasonality between glacial and interglacial periods this article examines why a conventional or sea surface temperature interpretation of the grip excess record seems inconsistent with inferred site and source temperature changes in addition the grip excess record is extended back into the penultimate glacial period and we assess its geographic significance through a comparison with existing dye 3 and north grip data we examine why low d 18o slopes observed during glacial times are associated with low deuterium excess values similarities between the greenland grip and antarctic vostok excess records are discussed in terms of potential links with insolation and insolation gradient changes finally the isotope records in specific do events are examined in light of intruiging differences between the isotope ratios d or 18o and the excess records that may result from a feedback mechanism linked with freshwater oceanic input

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

speleothem record of the last 180 ka in villars cave sw france investigation of a large δ18o shift between mis6 and mis5 the vil car 1 flowstone core from villars cave sw france provides one of the first european speleothem records extending back to 180 ka based on ueth tims and mc icp ms measurements the core offers a continuous record of termination ii and the last interglacial the penultimate deglaciation is characterized by a prominent 5 depletion in calcite d 18 o determining which specific environmental factors

new insights into southern hemisphere temperature changes from vostok ice cores using deuterium excess correction abstract the combination of both vostok ice core deuterium and deuterium excess histories over the last four climate cycles back to 420 ka bp offers a unique opportunity for reconstructions of vapor source region and local temperature variations tsource and tsite respectively relative to their modern values our study is based on an inversion of ice isotopic composition using a rayleigh based isotopic model which estimates the dependence of vostok precipitation isotopic composition on different climate controls moisture source temperature local deposition temperature and ocean isotopic composition both reconstructed local and source temperatures show no substantial effects from this correction in the sense that none of the rapid or large variations in raw deuterium and deuterium excess profiles can be entirely attributed to a second order climate control our discussion is focused on moisture source temperature and meridional temperature gradient history tsource tsite first using sea surface temperature time series we confirm that moisture source temperature signal recorded in vostok deuterium excess over the last 150 ka fully reflects the obliquity time varying relative contribution of low and high ocean latitudes to vostok precipitation second comparisons of source to site meridional temperature gradient with the vostok sodium record over 420 ka suggest that moisture transport and sea salt transport to the ice sheet are controlled by processes in different latitudes the sea salt being more of a high latitude signal

a synthesis of warm air advection to the south polar plateau surface temperature and wind chronologies of varying length and 10 m snow temperatures have been used to produce a synthesis of airflow into antarctica this synthesis shows relatively warm air over ellsworth land which appears to enter the south polar plateau through a slightly lower lying trough between the summit of the transantarctic mountains and the polar plateau comparison of recent automatic weather station aws records from mount howe 88 5 s 150 w with four aws surrounding south pole at 89 s show that this upslope inflow is a frequent and persistent phenomenon

record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years 1 we measured 17 o and 18 o in recent antarctic snow and down the vostok ice core and calculated the excess of 17 o with respect to vsmow the magnitude of the 17 o excess in the holocene and the last interglacial is 45 per meg and it remains constant in a transect from the coast to the continental interior analysis of the transect data shows that the 17 o excess is not sensitive to temperature variations over the continent there are significant shifts in 70 excess from low values in glacial to high values in interglacial times the observed shifts suggest higher normalized relative humidity and or wind speeds over the source oceanic regions in glacial times

sensitivity of chemical species to climatic changes in the last 45 kyr as revealed by high resolution dome c east antarctica ice core analysis

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

estimation of temperature change and of gas age ice age difference 108 kyr b p at vostok antarctica air trapped in ice core bubbles provides our primary source of information about past atmospheres air isotopic composition 15n 14n and 40ar 36ar permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets a rapid surface temperature change modifies temporarily the firn temperature gradient which causes a detectable anomaly in the isotopic composition of nitrogen and argon the location of this anomaly in depth characterizes the gas age ice age difference age during an abrupt event by correlation with the d or 18o anomaly in the ice we focus this study on the marine isotope stage 5d 5c transition 108 kyr b p a climate warming which was one of the most abrupt events in the vostok antarctica ice isotopic record petit et al 1999 a steplike decrease in 15n and 40ar 4 from 0 49 to 0 47 possibly a gravitational signal due to a change in firn thickness is preceded by a small but detectable 15n peak possibly a thermal diffusion signal we obtain an estimate of 5350 300 yr for age close to the model estimate of 5000 years obtained using the vostok glaciological timescale our results also suggest that the use of the present day spatial isotope temperature relationship slightly underestimates but by no more than 20 15 the vostok temperature change from present day at that time which is in contrast to the temperature estimate based on borehole temperature measurements in vostok which suggests that antarctic temperature changes are underestimated by up to 50 salamatin et al 1998

sea surface temperatures of southern midlatitudes 0 160 kyr b p 1 late quaternary climate fluctuated between extremes of glaciations lasting 90 kyr on average and interglacial episodes lasting 10 kyr still largely unknown are the spatial and temporal evolution of these global climate states with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations though it is widely believed that the southern hemisphere oceans play a central role in global climate changes few paleoclimate records exist from there here we present three new alkenone derived sst records from the midlatitude southern hemisphere spanning the last 160 kyr a full glacial interglacial cycle our subtropical sst records from the last glacial period are characterized by 1 warming 47 23 kyr b p when high latitudes in both hemispheres cooled and 2 milder temperatures during the penultimate glacial period than during the last glacial interval these sst features are found to be of tropical to subtropical wide extent implying increased thermal gradients at times of high latitude ice sheet growth this has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

twentieth century sea ice variability in the weddell sea and its effect on moisture transport evidence from a coastal east antarctic ice core record high resolution study of deuterium excess d excess sea salt sodium ss na and methane sulfonic acid msa in an ice core from coastal dronning maud land cdml east antarctica revealed the

water isotopes during the last glacial maximum new general circulation model calculations 1 the application of water isotopes to estimate the glacial interglacial cycle of temperature t assumes the validity of the present day spatial relationship between ta and 18o in precipitation 18op to estimate temporal changes of the temperature at a fixed location we explored how and why the spatial relationship between annual mean ta 18op is different from the temporal relationship at one location our general circulation isotope model exhibits a spatial slope of 1 22 c between annual mean temperature at the top of the inversion layer ti and 18op over antarctica comparable to the observed value of 1 25 c from dahe et al 1999 and using the phillpot and zillman 1970 relationship between surface temperature and the temperature of the inversion layer over the southern ocean 45 60 s local evaporation accounts for 50 of precipitation and this evaporative flux mean 18oe of 1 increases the 18o of vapor mean 18ov of 16 during the last glacial maximum lgm 21 000 years ago the isotopic composition of the vapor near the ice edge 60 s is calculated to be similar to the present values because evaporative recharge also accounts for 50 of the precipitation over the southern ocean as a result the isotopic composition of vapor during the lgm is close to the present values at the ice edge the apparent temporal slope over eastern antarctica is half of the observed spatial slope our lgm experiment estimates an antarctic mean annual temperature decrease of 13 c at vostok much larger than previous estimates our experiments with two specifications of lgm sea surface temperatures suggest that the value of the temporal slope is related to the temperature decrease over the southern ocean

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

assessment of alternative protection layers for a geomembrane geosynthetic clay liner gm gcl composite liner a protection layer is required above geomembrane gm geosynthetic clay liner gcl landfill liners to limit physical damage gm strains and gcl thinning from an overlying granular drainage layer a 150 mm thick layer of sand has been found to provide excellent protection at a vertical pressure of 250 kpa however the use of sand may not be practical in many cases experimental results are presented where the effectiveness of alternate protection systems above one particular gm gcl liner were examined with 50 mm coarse gravel at an applied vertical pressure of 250 kpa a 150 mm thick layer of compacted clay and a 150 mm thick layer of rubber tire shreds with a nonwoven needle punched geotextile 570 g m2 were found to limit the geomembrane strains and gcl extrusion to acceptable levels layered geotextiles performed much better than single layers of geotextiles a layered geocomposite with a thick nonwoven needle punched geotextile in the middle to provide cushioning and stiffer woven geotextiles on

implications of the glacial co2 iron hypothesis for quaternary climate change 1 the iron hypothesis posits a role for increased supply of mineral aerosol to the ocean surface during glacial periods in driving atmospheric co2 lower that changes in co2 and climate strongly affect dust supply raises the possibility of feedback here i take a systems view in analyzing the properties and implications of such a feedback and consider three primary state variables that can be related empirically to each other dust supply atmospheric co2 and climate surface air temperature the results of this analysis suggest that the dust co2 climate feedback is primarily an intraglacial phenomenon when it can account for about a third of the temperature variability recorded in antarctic ice cores since glacial interglacial cyclicity prior to ca 800 kyr bp is characterized by the absence of a full glacial state such as the last glacial maximum it is possible that destabilization of climate by the marine iron cycle is fundamental to the differences between 41 kyr and 100 kyr climatic regimes the critical role played by the state of the land surface in this feedback also has implications for the longer term evolution of the earth system during the cenozoic

water isotopes as tools to document oceanic sources of precipitation the isotopic composition of precipitation in deuterium oxygen 18 and oxygen 17 depends on the climatic conditions prevailing in the oceanic regions where it originates mainly the sea surface temperature and the relative humidity of air this dependency applies to present day precipitation but also to past records which are extracted for example from polar ice cores in turn coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air this interpretation of isotopic measurements has largely relied on simple rayleigh type isotopic models and is complemented by lagrangian back trajectory analysis of moisture sources it is now complemented by isotopic general circulation models igcm in which the origin of precipitation can be tagged we shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition we then present experiments performed with two different igcms the giss model ii and the lmdz model we focus our study on marine water vapor and its contribution to precipitation over antarctica and over the andean region of south america we show how igcm experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition such experiments support at least qualitatively the current interpretation of ice core isotopic data in terms of changes in sea surface temperature additionally we discuss recent studies clearly showing the added value of oxygen 17 measurements key points link between the isotopic content of precipitation and its oceanic origin application of this method to polar ice cores andean precipitation potential of combining deuterium excess and oxygen 17 excess 2013 american geophysical union all rights reserved

recent changes in bottom water oxygenation and temperature in the gulf of st lawrence micropaleontological and geochemical evidence micropaleontological and geochemical analyses of a sediment core collected in the laurentian trough of the gulf of st lawrence were carried out to reconstruct temporal variations in pelagic productivity and benthic environmental conditions dinoflagellate cyst assemblages reveal relatively stable pelagic productivity over the last two centuries similarly geochemical organic c corg n and isotopic d13corg d15n data reveal that organic matter fluxes to the seafloor have been relatively constant over the same period in contrast significant changes are recorded in the benthic foraminifer assemblages a sediment surface peak in the abundance of cassidulina laevigata and brizalina subaenariensis is consistent with the recent record of oxygen depletion in the bottom water a decrease in the relative abundance of nonionellina labradorica concomitant with a relatively higher occurrence of oridorsalis umbonatus in the upper part of the core reflects a significant warming of the bottom water changes in bottom water properties are further constrained by a negative trend of the d18 oi n bulimina exilis carbonate shells over the last century corresponding to a warming of about 2uc these results strongly suggest that the recent oxygen depletion in the bottom waters of the gulf of st lawrence is due to changes in water masses that have led to increased bottom water temperatures and to some extent a resultant increase in organic matter respiration rates

hydraulic performance of overlapped geosynthetic clay liner seams requiring field applied supplemental bentonite abstractthis article investigates the hydraulic performance of geosynthetic clay liner gcl overlapped seams subjected to nonuniform stresses due to a wrinkle in an overlying geomembrane the performance when the gcl seam was parallel to and directly below a wrinkle depended on the width of the gcl seam relative to the deformed wrinkle when both ends of the seam were confined under vertical stress from the deformed wrinkle there was no evidence of preferential flow along the seam and the magnitude of flow was slightly smaller than the case with just a single intact gcl panel beneath the wrinkle flow through the gcl seam when perpendicular to a wrinkle was mostly affected by the presence and distribution of supplemental bentonite with no supplemental bentonite flow was 370 times greater than that through an intact gcl panel beneath the wrinkle application of 400 g m of supplemental bentonite piled along the center of the seam decreased the flow by more than two orders of magnitude compared with ha

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

what was the surface temperature in central antarctica during the last glacial maximum abstract the temperature increase at vostok antarctica from the last glacial maximum to the present warm period is about 8 c based on the deuterium isotope profile the bore hole temperature temperature profile in the ice sheet indicates that the temperature difference may have been much larger about 15 c the temperature dependent gas occlusion process is the key to evaluate the two scenarios atmospheric air penetrates the porous firn layer of the ice sheet and gets trapped at the firn ice boundary consequently the air is younger than the surrounding ice when it gets enclosed in bubbles this age difference age between ice and enclosed gas is temperature and accumulation rate dependent therefore it is possible to estimate paleotemperatures from a known age we use the linkage between chronologies of ch 4 and water isotopes from byrd station and vostok to obtain an experimental age for vostok this experimental age is then compared to modeled age for the two temperature scenarios our results indicate that the temperature reconstruction deduced from the water isotopic composition is the more probable one

glacial interglacial changes in ocean surface conditions in the southern hemisphere the stable isotope signatures of oxygen and hydrogen in the water of preserved ice and snow are both widely used to infer local temperatures of past environments a derived quantity based on these two signatures the deuterium excess 1 provides additional palaeoclimatic information2 3 4 as this parameter depends on the meteorological and oceanic characteristics of the water s source regions in particular their temperature2 3 and relative humidity4 published studies mainly focus on records from the past 40 000 years here we present a deuterium excess history obtained from ice cores from vostok east antarctica spanning the full glacial interglacial cycle of the past 150 000 years the deuterium excess record shows a strong anticorrelation with the earth s orbital obliquity 41 000 year periodicity and values are markedly higher during the cold stage 5d following the last interglacial than during the other cold stages we interpret the relationship with obliquity as resulting from changes in the latitudinal insolation gradient affecting ocean surface conditions and thus the delivery of moisture to the polar region we argue that the high 5d values relative to other cold stages are driven by relatively less moisture delivered from high latitudes and more from low latitudes the deuterium excess in antarctic precipitation thus provides long term spatially integrated information on ocean surface conditions and ocean atmosphere circulations in the southern hemisphere

chemical composition of volcanic glasses in visible tephra layers found in a 2503 m deep ice core from dome fuji antarctica twenty six ash layers were found in a 2503 m deep ice core from dome fuji station east antarctica in order to gain information about the sources of ash particles found in the layers major and trace element abundances have been measured the particles found in 21 of the 26 layers were commonly a few tens of m in size suggesting that they originated from volcanoes located in and around the antarctic on the basis of comparison of the major element compositions of these tephras with reference to volcanic rocks and ash the tephras were divided into three types 1 tholeiitic basalt to dacite 2 calc alkaline andesite and 3 trachyandesite to trachyte the source regions appear to be 1 south sandwich islands southern ocean 2 south shetland islands antarctica and or a southern part of the volcanic zone of the andes and 3 marie byrd land and or victoria land antarctica respectively the tephras found in the other five ash layers were significantly smaller 5 m suggesting that they traveled over longer distances abundances of trace elements for the alkaline tephra collected from one layer revealed a possible genetic link to volcanic rocks from marie byrd land in order to correlate between ice cores from dome fuji and vostok antarctica which are widely separated we found coeval ash layers serving as stratigraphic markers of antarctic ice cores a comparison of profiles of 18o 16o 18o and 2h 1h d for the dome fuji and vostok cores indicates that eight ash layers are equivalent in the two cores a clear correlation was found for the chemical compositions of six of these ash layers indicating a high potential for key correlation beds between the deep ice cores from dome fuji and vostok

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

sea ice control of water isotope transport to antarctica and implications for ice core interpretation 1 sea ice in the southern ocean is important for antarctic climate and hydrology the dependence of water isotope abundance 18o and deuterium excess on the winter sea ice state is examined with the isotopic version of the melbourne university general circulation model reductions in the ice concentration provide warmer temperatures in winter and allow higher precipitation totals further south while the reverse occurs with increased ice extent the model shows clear demarcation between the changes in the isotopic conditions over the sea ice pack where local changes in surface exchange dominate and those of the continent interior which depend on the long ranged transport aloft while less sensitive to the forcing the interior response is influenced by changes in turbulent mixing over the ice pack and modification of the vertical transport associated with diabatic heating the interior deuterium excess response is more strongly affected by sea ice as it captures changes in temperature over the ice rather than just the final vapor mass traditional reconstruction of temperature from a single isotopic nuclide would give erroneous interpretation of change in the global mean temperature unless the sea ice changes in parallel instead the spatial structure of the sea ice response gives some hope for extracting past sea ice conditions from multicore analysis this study begins to explore the role of entropy production during transport such that the isotopic interpretation is more closely tied to the dynamics of the atmosphere than is expressed by idealized parcel analysis

geochemical characteristics of lake clay drilled in well qz 4 its implication for geochemical response to climate change in the central tibetan plateau in the middle late pleistocene a colour sequence which is composed of a yellow subsequence in the lower unit and a grey subsequence in the upper unit is an important climate archive for the central tibetan plateau in the middle late pleistocene however little study has been done on it in well qz 4 this colour sequence is thicker than 116 m which is an important climate archive for the central tibetan plateau in the middle late pleistocene in this work the esr dating and geochemistry analysis have been carried out to provide a preliminary insight into the paleo climate change in the central tibetan plateau it can be concluded that the 23 56 ka 125 96 149 52 ka bp time interval which is marked by the angular unconformity surface at 272 48 m in depth proves that the deposition of this colour sequence is dominated by gonghe movement after this movement chemical weathering is reduced however the sedimentation rate is increased from 0 18 to 3 5 m ka in the central tibetan plateau the climate became colder and drier in the middle late pleistocene which is roughly consistent with global paleo climate change at that time all these changes are correlated with the change of elevation and atmospheric circulation in the tibetan plateau and its surrounding area which are driven by the tectonic uplift of gonghe movement the gonghe movement is likely a driving force for the short lived spike at about 120 ka

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

glacial dynamics in southernmost south america during marine isotope stage 5e to the younger dryas chron a brief review with a focus on cosmogenic nuclide measurements the timing of major glacial changes between marine isotope stage mis 5e and the younger dryas chron yd in southern south america is reviewed focus is placed on studies that use cosmogenic nuclide measurements however other dated records and modelling results are also discussed to provide the broader glacial geological context limits on the state of glacial geologic knowledge are examined and suggestions are made as to how some of these can be addressed in future studies studies show that on the east side of the andes at lago buenos aires 45 s there is evidence indicating that following a mis 6 glaciation ice was less extensive during mis 4 than mis 2 in contrast on the west side of the andes in the chilean lake district area mis 4 ice may have been more extensive than during mis 2 although patagonia experienced an mis 2 glaciation broadly in phase with that in other areas around the globe there are differences in glacial histories between areas on millennial timescales climate reversals are evident in many records between ca 17 and 10 ka the timing of such lateglacial activity which included less extensive advances than during the local last glacial maximum lgm varies somewhat between areas this could be due to the relative influence of middle to high latitude climatic regimes at present chronological uncertainties prevent confident assignment of cosmogenic ages for glacial events at the millennial timescale and defining associated climate variability between different study areas copyright 2008 john wiley sons ltd