climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

a generalized additive model for the spatial distribution of stable isotopic composition in antarctic surface snow abstract using the most recent compilation of surface antarctic snow isotopic composition data and a 1 km resolution digital elevation model dem a generalized additive model gam was used to develop a new gridded map of stable isotopic composition in antarctic surface snow the model explained 93 9 of the observed variance in the 18 o data 92 7 of the observed d variance and 66 6 of the observed deuterium excess the performance of the model was evaluated by applying different quantitative approaches to the residuals from a cross validation test this modeling approach is a useful tool for interpolating local surface snow isotopic composition over antarctica both in terms of the low estimated errors and the possibility of understanding the processes that control stable isotopic composition in antarctic surface snow through the response curves of each independent variable we also presented and interpreted the resulting spatial variation patterns of 18 o d and deuterium excess to better use in many hydrological and paleoclimate applications

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

effects of firn ventilation on isotopic exchange a new model of isotopic diffusion in the upper few meters of firn tracks the isotopic composition of both the ice matrix and the pore space vapor through time in two dimensions stable isotopes in the vapor phase move through the firn by diffusion along concentration gradients and by advection wind driven ventilation carries atmospheric water vapor into the firn where it mixes with existing pore space vapor unlike previous models our model allows disequilibrium between pore space vapor and the surrounding snow grains we also calculate the isotopic effects of ventilation driven sublimation and condensation in the firn model predictions of isotopic diffusion in firn compare favorably with existing diffusion models model results quantify what other investigators have suggested isotopic change in the upper few meters is more rapid than can be explained by the whillans and grootes 1985 model isotopic equilibration with atmospheric vapor is an important component of post depositional isotopic change and ventilation enhances isotopic exchange by creating regions of relatively rapid sublimation and condensation in the firn

spatial and temporal variability in isotope composition of recent snow in the vicinity of vostok station antarctica implications for ice core record interpretation continuous detailedisotope ddandd 18 o profileswereobtainedfrom eight snow pits dug in the vicinity of vostok station antarctica during the period1984 2000 in addition snow samples taken along the 1km long accumulation stake profile were measured to determine spatial variability in isotope composition of recent snow the stacked dd time series spanning the last 55years shows only weak correlation with the mean annual air temperature recorded at vostok station significant oscillations of both snow accumulation and snow isotope composition with the periods 2 5 5 20 and possibly 10 2 years observed at single points are interpreted in terms of drift of snow accumulationwaves of various scales onthe surface of the ice sheet

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

what drives the millennial and orbital variations of δ18oatm abstract the isotopic composition of atmospheric oxygen 18oatm is a complex marker that integrates changes in global sea level water cycle and biosphere productivity a strong signature of orbital precession has been identified leading to the use of low resolution measurements of 18oatm to date ice core records however the drivers of these 18oatm variations are still poorly known here we combine records of millennial and orbital scale variations on the northgrip vostok and epica dome c edc ice cores to explore the origin of 18oatm variations we show that superimposed on the dominant precession signal millennial 18oatm variations record systematic decreases during warm phases of the dansgaard oeschger events and systematic increases during the cold phases we show that at both timescales 18oatm is strongly related to the monsoon activity itself influenced by precessional and millennial shifts in intertropical convergence zone itcz then we show that despite its simplicity the dole effect defined as the difference between 18oatm and 18o of global sea level enables one to remove the obliquity signal within the 18oatm record and is a good indicator of hydrological cycle and biosphere productivity finally we compare the 18oatm records to past changes in atmospheric composition recorded in ice cores and conclude that 18oatm responds much more than ch4 to precession signal in contrast with earlier views similarities observed at orbital timescales between co2 and 18oatm reveal a stronger coupling than previously thought between the carbon and the oxygen cycles

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

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

multidisciplinary tephrochronological correlation of marker events in the eastern tyrrhenian sea between 48 and 105 ka abstract the basal portion 2 92 5 08 m from core top of the cet1 core located in a bathyal area of the eastern tyrrhenian sea is the subject of a multidisciplinary investigation encompassing tephrostratigraphy quantitative analyses of planktonic foraminifera and calcareous nannofossil assemblages and 18o measurements supported by a 40ar 39ar age determination calcareous nannofossil assemblages allowed the attribution of the analyzed sediments to the biozone mmn21a and the succession spans from more than 48 to ca 105 ka although there are at least two stratigraphic gaps and minor resedimentation episodes a paleoclimatic reconstruction obtained via 18o and planktonic foraminifera data identifies several of the major climatic events that occurred in the investigated time span a total of 13 visible tephra layers and cryptotephras are recognized and correlated with their volcanic sources campanian volcanic zone and pantelleria volcano and when possible with well known and dated events or with widespread marker tephras using a combination of biostratigraphic oxygen isotope and tephrostratigraphic correlations we develop a chronostratigraphy for the main climatic events and tephra layers in the core and pinpoint tephra markers for the climatic events comprised between gs 22 and gi 24 in the eastern tyrrhenian sea

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

seasonal variations of accumulation and the isotope record in ice cores a study with surface snow samples and firn cores from neumayer station antarctica at the german wintering base neumayer an intensive glacio meteorological program was carried out during the last two decades a complete meteorological data set and data from surface snow samples snow pits firn cores and weekly accumulation measurements from a stake array are available we first investigated the attenuation of the seasonal d18o signal due to water vapour diffusion in the snow pack a comparison of surface snow samples and firn cores of different age shows that only one third of the seasonal d18o signal of the surface snow samples remains in the cores after the first year no further significant change in the amplitude of the seasonal d18o signal is found later changes in the seasonal distribution of accumulation can lead to a bias in ice core properties this is studied on a short time scale using the available high time resolution data of accumulation stable isotope ratios and air temperature mean annual d18o values from firn cores are not well correlated to annual mean air temperatures however the correlation is improved considerably by weighting the annual mean air temperature by accumulation at neumayer mainly the cyclonic activity in late winter early spring determines whether and how the core data are biased

development of an antarctic digital elevation model by integrating cartographic and remotely sensed data a geographic information system based approach we present a high resolution digital elevation model dem of the antarctic it was created in a geographic information system gis environment by integrating the best available topographic data from a variety of sources extensive gis based error detection and correction operations ensured that our dem is free of gross errors the carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data the effective control of adverse edge effects and the use of the hermite blending weight function in data merging minimized the discontinuities between different types of data leading to a seamless and topographically consistent dem throughout the antarctic this new dem provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier continental scale renditions particularly in mountainous and coastal regions it has a horizontal resolution of 200 m over the rugged mountains 400 m in the coastal regions and approximately 5 km in the interior the vertical accuracy of the dem is estimated at about 100 130 m over the rugged mountainous area better than 2 m for the ice shelves better than 15 m for the interior ice sheet and about 35 m for the steeper ice sheet perimeter the antarctic dem can be obtained from the authors

global budget of water isotopes inferred from polar ice sheets 1 water isotope ratios in ice cores and marine sediments are a key indicator of past temperature and global ice volume quantitative interpretation of these ratios requires understanding of the storage capacity and exchanges among the ocean atmosphere and cryosphere we combine numerical models of ice dynamics and tracer transport to predict bulk ice properties by simulating the fine layering of ice sheets locally validated at ice core sites the 18o 16o content of ice sheets is found to vary between the present and 20 kyr ago from 34 to 37 for greenland from 41 to 42 5 for west antarctica and always remained near 56 5 for east antarctica their combined effect on sea water 18o 16o is a 0 08 0 12 increase 20 kyr ago a 1 11 decrease if ice sheets were to vanish we confirm that ice volume changes in antarctica and greenland linearly affect ocean composition though at different rates

atmospheric influence on the deuterium excess signal in polar firn implications for ice core interpretation the seasonal deuterium excess signal of fresh snow samples from neumayer station coastal dronning maud land antarctica was studied to investigate the relationship between deuterium excess and precipitation origin an isotope model was combined with a trajectory model to determine the relative influence of different moisture sources on the mean annual course of the deuterium excess focusing on the phase lag between d 18 o and excess d whereas the annual course of d 18 o always shows an austral summer maximum which clearly depends on local temperature and the annual course of moisture source area parameters the deuterium excess of the fresh snow samples shows maximum values already in spring there can be many different reasons for the time lag between d 18 o and deuterium excess in an ice core including post depositional processes and changes in the moisture source of precipitation the use of fresh snow samples enabled us to exclude post depositional processes and study solely the influence of precipitation origin changes in the moisture source connected to systematic changes in the general atmospheric circulation can have a strong influence on the phase lag between deuterium excess and d 18 o which has to be taken into account for climatic interpretation of stable isotope profiles from ice cores

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

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

the effect of temporal variations in the surface mass balance and temperature inversion strength on the interpretation of ice core signals the proxy for temperature signal in ice cores is stored in the snow ice during precipitation events and hence reflects the temperature at which precipitation is formed here approximated by the inversion temperature t weighted with the accumulation results from a 14 year integration 1980 93 with a regional atmospheric model racmo x 55 km show that the annual mean accumulation weighted inversion temperature t i w and the annual mean t i are not covariant in time at four out of the five deep drilling sites considered mainly due to year to year variations in the seasonality of precipitation as a consequence the surface temperature t s core derived from racmo output using a method analogous to the retrieval of the surface temperature from ice core signals deviates from the directly modelled surface temperature t s on interannual time scales results from a 5 year sensitivity integration forced with a 2 k temperature increase show an 18 overestimation of the increase in t s core relative to the increase in t s due to a change in the relationship between the inversion strength and the surface temperature in a different climate regime similar errors may occur in deriving the temperature difference between last glacial maximum and present day climate from signals in ice cores

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

a continuous record of temperature evolution over a sequence of dansgaard oeschger events during marine isotopic stage 4 76 to 62 kyr bp 1 our knowledge of the temperature evolution over greenland during dansgaard oeschger events do is currently qualitatively described through the water isotopic profile using two independent paleothermometry methods one based on air isotopic measurements and the other on the combined measurements of water isotopes dd and d 18 o we show a complete and quantitative reconstruction of temperature at the northgrip site over the period 76 to 62 kyr bp do 18 19 and 20 we confirm that the associated warmings are larger than those conventionally depicted by the water isotopes 11 c 16 c and 11 c for do 18 19 and 20 secondly we demonstrate that the relationship between temperature and d 18 o varies rapidly during the last glacial period even over a do finally our temperature reconstruction over do 19 agrees well with that predicted from simple climate models linking the do to iceberg discharges 2004 a continuous record of temperature evolution over a sequence of dansgaard oeschger events during marine isotopic stage 4 76 to 62 kyr bp geophys res lett 31 l22211 doi 10 1029 2004gl021193 2 the last glacial cycle was characterized by millenial scale climate fluctuations that have been documented in the north atlantic region through numerous marine and continental records bond et al 1997 genty et al 2003 the grip and gisp2 summit ice cores dansgaard et al 1993 grootes et al 1993 and the newly northgrip northgrip members 2004 ice core exhibit 25 do during the last glacial period these events are characterized by rapid e g in less than 100 years and large up to 16 c lang et al 1999 warmings over greenland 3 ice cores have already provided a wealth of information on do in greenland through the water isotopes for temperature changes chemical records for atmospheric circulation and analysis of air bubbles for changes in greenhouse gases concentration however temperature reconstruction from water isotopes is subject to large biases mainly due to i the seasonality of the precipitation i e periods without precipitation will not have their temperature recorded fawcett et al 1997 and ii changes in the oceanic source of greenland snow boyle 1997 whereas the latter can be estimated from the combined measurement of dd and d 18 o through the deuterium excess parameter d dd a 8 d 18 o we need additional information to account for the influence of seasonality and possible variation of the vertical atmospheric temperature profile the isotopic composition of the snow depends on the condensation temperature 4 one elegant way to overcome those difficulties is to use the isotopic composition of the air trapped in ice a method based on the thermal diffusion of gases nitrogen and argon which allows estimates of the amplitude of rapid temperature increases severinghaus and brook 1999 lang et al 1999 leuenberger et al 1999 this method gives directly access to the local mean surface temperature and is therefore not affected by seasonality the vertical temperature profile in the atmosphere nor the source temperature of the precipitation it confirms that the conventional temperature to water isotopes relationship based on the spatial slope a s the dd 18 o ice temperature slope calculated from present day surface data underestimates greenland temperature change cuffey et al 1995 the temporal slope a t dd 18 o ice dt at a given site between two different climates is lower than a s by up to a factor of 2 we have recently refined this approach using a sophisticated firnification and heat diffusion model goujon et al 2003 to quantify the temperature increase associated with large do 12 landais et al 2004 5 here we go beyond the simple quantification of the temperature increase a detailed set of d 15 n and d 40 ar measurements over do 18 19 and 20 provides us with strong constraints on the complete temperature scenario between 76 and 62 kyr bp this period roughly corresponds to marine isotope stage 4 with rapid ice sheet growth shackleton 1987 we have also measured a continuous dd profile in the ice that combined with the existing d 18 o record allows us to account for the source temperature effects this complete study makes possible the precise estimation of the temperature change over a sequence of do 6 the d 15 n and d 40 ar profiles figure 1 show a sharp peak corresponding to each warming rapid surface warm geophysical research letters vol 31 l22211

the origin of present day antarctic precipitation from surface snow deuterium excess data the deuterium excess d is defined as a linear combination of the d h and 18 o 16 o ratios in natural waters we present an interpretation of deuterium excess data in surface antarctic snow using an isotopic model to derive information on the origin of present day antarctic precipitation the data come from near the coast d47 adelie land and from inland south pole 1000 km from the sea the one dimensional isotopic model belongs to the rayleigh family but fully accounts for mixed cloud processes between 0 c and 30 c modeling d in polar snowfalls meets the problem of a large sensitivity to the saturation conditions prevailing at snow formation therefore we decided to tune the saturation in the model in order to yield realistic mean d values but we use the seasonal phase of d versus which is less sensitive to the saturation conditions as an independent validation of the model predictions both inland and near the coast our model can simulate the observed phase between d and in snow with moisture of subtropical origin 40 20 s although we do not treat specifically storm precipitation near the coast this study indicates that the observed phase between d and brings up a new validation of isotopic models it supports a distant vapor source for large scale precipitation delivered to the antarctic continent