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Using new high resolution 10Be measurements in the NGRIP, EDML and Vostok ice cores, together with previously published data from EDC, we present an improved synchronization between Greenland and Antarctic ice cores during the Laschamp geomagnetic excursion ~ 41 ky ago. We estimate the precision of this synchronization to be ± 20 years, an order of magnitude better than our previous work. We discuss the implications of this new synchronization for making improved estimates of the difference between ice and enclosed gas of the same age (delta depth), difference between age of ice and enclosed gas at the same depth (delta age) in the EDC and EDML ice cores, spectral properties of the 10Be profiles and phasing between Dansgaard/Oeschger-10 (in NGRIP) and AIM-10 (in EDML and EDC). [ABSTRACT FROM AUTHOR]

Improvements in the evaluation of land surface models would translate into more reliable predictions of future climate changes, as significant uncertainties persist in the quantification and representation of the relative contributions of soil and vegetation to the water and energy cycles. In this paper, we investigate the usefulness of water stable isotopes in land surface models studying land surface processes. To achieve this, we implemented 18O and ²H and the computation of the oxygen (δ18O) and deuterium (δD) stable isotope composition of soil and leaf water pools in a recent version of the land surface model ORCHIDEE. We performed point-wise simulations with this new model and evaluated its performance on vertical profiles of soil water isotope ratios measured in summer 2012 at four experimental sites located in a boreal region of the Artic zone of western Siberia. The model performed relatively well in simulating some features of the δ18O soil profiles, but poorly reproduced the d-excess profiles, at all four stations. The response of the simulated δ18O profiles to variations in key hydrological parameters revealed the importance of the choice of a correct infiltration pathway in ORCHIDEE. Our results show also that the strength of the evaporative enrichment signal plays a role in shaping the profiles, too and, therefore, the relevance of the vegetation and bare soil characterization. We investigated furthermore to which extent we are able to determine the relative contribution of the evaporation to the evapotranspiration. This study's results confirm that the use of water stable isotopes measurements helps constrain the representation of key land surface processes in land surface models. [ABSTRACT FROM AUTHOR]

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice-bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica. [ABSTRACT FROM AUTHOR]

Ice cores are exceptional archives which allow us to reconstruct a wealth of climatic parameters as well as past atmospheric composition over the last 800 kyr in Antarctica. Inferring the variations in past accumulation rate in polar regions is essential both for documenting past climate and for ice core chronology. On the East Antarctic Plateau, the accumulation rate is so small that annual layers cannot be identified and accumulation rate is mainly deduced from the water isotopic composition assuming constant temporal relationships between temperature, water isotopic composition and accumulation rate. Such an assumption leads to large uncertainties on the reconstructed past accumulation rate. Here, we use high-resolution beryllium-10 (10Be) as an alternative tool for inferring past accumulation rate for the EPICA Dome C ice core, in East Antarctica. We present a high-resolution 10Be record covering a full climatic cycle over the period 269 to 355 ka from Marine Isotope Stage (MIS) 9 to 10, including a period warmer than pre-industrial (MIS 9.3 optimum). After correcting 10Be for the estimated effect of the palaeomagnetic field, we deduce that the 10Be reconstruction is in reasonably good agreement with EDC3 values for the full cycle except for the period warmer than present. For the latter, the accumulation is up to 13% larger (4.46 cm ie yr-1 instead of 3.95). This result is in agreement with the studies suggesting an underestimation of the deuterium-based accumulation for the optimum of the Holocene (Parrenin et al., 2007a). Using the relationship between accumulation rate and surface temperature from the saturation vapour relationship, the 10B e-based accumulation rate reconstruction suggests that the temperature increase between the MIS 9.3 optimum and present day may be 2.4 K warmer than estimated by the water isotopes reconstruction. We compare these reconstructions to the available model results from CMIP5-PMIP3 for a glacial and an interglacial state, i.e. for the Last Glacial Maximum and pre-industrial climates. While 3 out of 7 models show relatively good agreement with the reconstructions of the accumulation-temperature relationships based on 10Be and water isotopes, the other models either underestimate or overestimate it, resulting in a range of model results much larger than the range of the reconstructions. Indeed, the models can encounter some difficulties in simulating precipitation changes linked with temperature or water isotope content on the East Antarctic Plateau during glacial-interglacial transition and need to be improved in the future. [ABSTRACT FROM AUTHOR]

Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousand of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using δ18Oatm, δO2/N2 and air content with di erent orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of δO2/N2 and δ18Oatm data encompassing Marine Isotopic Stage (MIS) 5 (between 100-160 ka) and the oldest part (380-800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of δO2/N2 and δ18Oatm records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights a site-specific relationship between δO2/N2 and its local summer solstice insolation. Such a relationship increases the uncertainty associated with the use of δO2/N2 as a tool for orbital tuning. Combining records of δ18Oatm and δO2/N2 from Vostok and EDC, we evidence a loss of orbital signature for these two parameters during periods of minimum eccentricity (~ 400, ~ 720-800 ka). Our dataset reveals a time-varying lag between δO2/N2 and δ18Oatm over the last 800 ka that we interpret as variations of the lag between δ18Oatm and precession. Large lags of ~ 5 ka are identified during Terminations I and II, associated with strong Heinrich events. On the opposite, minimal lags (~ 1-2 ka) are identified during four periods characterized by high eccentricity, intermediate ice volume and no Heinrich events (MIS 6-7, the end of MIS 9, MIS 15 and MIS 17). We therefore suggest that the occurrence of Heinrich events influences the response of δ18Oatm to precession. [ABSTRACT FROM AUTHOR]

Continuous, in situ measurements of water vapor isotopic composition have been conducted in the North Atlantic, at the Bermuda Islands (32.26° N, 64.88° W), between November 2011 and June 2013, using a cavity ringdown spectrometer water vapor isotope analyzer and an autonomous self-designed calibration system. Meticulous calibration allows us to reach an accuracy and precision on 10 min average of δ18O, δD, and d-excess of, 0.14, 0.85, and 1.1 %o, verified using two parallel instruments with independent calibration. As a result of more than 500 days with 6- hourly data the relationships between deuterium excess, relative humidity (RH), sea surface temperature (SST), wind speed, and wind direction are assessed. From the whole data set, 84 % of d-excess variance is explained by a strong linear relationship with relative humidity. The slope of this relationship (-42.6 ± 0.4 %% (RH)) is similar to the theoretical prediction of Merlivat and Jouzel (1979) for SST between 20 and 30 °C. However, in contrast with theory, no effect of wind speed could be detected on the relationship between d-excess and relative humidity. Separating the data set into winter, spring, summer, and autumn seasons reveals different linear relationships between d-excess and humidity. Changes in wind directions are observed to affect the relationships between d-excess and humidity. The observed seasonal variability in the relationship between d-excess and relative humidity underlines the importance of long-term monitoring to make accurate conclusions. [ABSTRACT FROM AUTHOR]

Ice cores are exceptional archives which allow us to reconstruct a wealth of climatic parameters as well as past atmospheric composition over the last 800 ka in Antarctica. Inferring the variations of past accumulation rate in polar regions is essential both for documenting past climate and for ice core chronology. On the East Antarctic plateau, the accumulation rate is so small that annual layers cannot be identified and accumulation rate is mainly deduced from the water isotopic composition assuming constant temporal relationships between temperature, water isotopic composition and accumulation rate. Such assumption leads to large uncertainties on the reconstructed past accumulation rate. Here, we use high resolution beryllium-10 (10Be) as an alternative tool for inferring past accumulation rate for the EPICA Dome C ice core, in East Antarctica. We present a high resolution 10Be record covering a full climatic cycle over the period 269 to 355 kyr BP from MIS 9 to MIS 10 (Marine Isotope Stages). After correcting 10Be for the estimated effect of the paleomagnetic field, we deduce that the classical estimation of accumulation rate variations from records of water isotopes agrees, with a possible underestimation of 16%, with the uncertainty on the temperature reconstruction from water isotopes in Antarctic ice cores. This is within their uncertainty of -10 to +30%. Finally, we show that the relationship between temperature and accumulation rate is comparable when using ice core data and results from several AGCM simulations run on glacial-interglacial conditions despite a larger spread in model outputs. These results indicate that the thermodynamic law linking moisture content in the air and temperature, as implemented in the different models, leads to realistic results even in polar regions, at the end of the water distillation trajectory. [ABSTRACT FROM AUTHOR]

Global warming is associated with large increases in surface air temperature in Siberia. Here, we apply the isotope-enabled atmospheric general circulation model ECHAM5-wiso to explore the potential of water isotope measurements at a recently opened monitoring station in Kourovka (57.04° N, 59.55° E) in order to successfully trace climate change in western Siberia. Our model is constrained to atmospheric reanalysis fields for the period 1957-2013 to facilitate the comparison with observations of δD in total column water vapour from the GOSAT satellite, and with precipitation δ18O measurements from 15 Russian stations of the Global Network of Isotopes in Precipitation. The model captures the observed Russian climate within reasonable error margins, and displays the observed isotopic gradients associated with increasing continentality and decreasing meridional temperatures. The model also reproduces the observed seasonal cycle of δ18O, which parallels the seasonal cycle of temperature and ranges from -25‰ in winter to -5‰ in summer. Investigating West Siberian climate and precipitation δ18O variability during the last 50 years, we find long-term increasing trends in temperature and δ18O, while precipitation trends are uncertain. During the last 50 years, winter temperatures have increased by 1.7 °C. The simulated long-term increase of precipitation δ18O is at the detection limit (<1‰ per 50 years) but significant. West Siberian climate is characterized by strong interannual variability, which in winter is strongly related to the North Atlantic Oscillation. In winter, regional temperature is the predominant factor controlling δ18O variations on interannual to decadal timescales with a slope of about 0.5‰ °C-1. In summer, the interannual variability of δ18O can be attributed to shortterm, regional-scale processes such as evaporation and convective precipitation. This finding suggests that precipitation δ18O has the potential to reveal hydrometeorological regime shifts in western Siberia which are otherwise difficult to identify. Focusing on Kourovka, the simulated evolution of temperature, δ18O and, to a smaller extent, precipitation during the last 50 years is synchronous with model results averaged over all of western Siberia, suggesting that this site will be representative to monitor future isotopic changes in the entire region. [ABSTRACT FROM AUTHOR]

We evaluate the isotopic composition of water vapor and precipitation simulated by the LMDZ GCM over Siberia using several datasets: TES and GOSAT satellite observations of tropospheric water vapor, GNIP and SNIP precipitation networks, and daily, in-situ measurements of water vapor and precipitation at the Kourovka site in Western Siberia. We use δD vs. humidity diagrams to explore the complementarity of these two variables to interpret model biases in terms of the representation of processes. LMDZ captures the spatial, seasonal and daily variations reasonably well. It systematically overestimates δD in the vapor and precipitation, a bias that is most likely associated with a misrepresentation of air mass origin. The performance of LMDZ is put in the context of other isotopic models from the SWING2 models. There is significant spread among models in the simulation of δD, and of the δD vs. humidity relationship. This confirms that δD brings additional information compared to humidity only. We specifically investigate the added value of water isotopic measurements to interpret the warm and dry bias feature by most GCMs over mid and high latitude continents in summer. LMDZ simulates the strongest dry bias on days when it simulates the strongest enriched bias in δD. The analysis of the slopes in δD vs. humidity diagrams and of processes controlling δD and humidity variations suggests that the cause of the moist bias could be either a problem in the large-scale advection transporting too much dry and warm air from the south, or insufficient surface evaporation. [ABSTRACT FROM AUTHOR]

Global warming is associated with large increase in surface air temperature and precipitation in Siberia. Here, we apply the isotope-enhanced atmospheric general circulation model ECHAM5-wiso to investigate the variability of δ18O in West Siberian precipitation and the underlying mechanisms during the last fifty years, and to assess the potential of a recently opened monitoring station in Kourovka (57.04° N, 59.55° E) to successfully track large-scale water cycle and climate change in this area. Our model is constrained to atmospheric reanalysis fields to facilitate the comparison with precipitation δ18O from observations. In Russia, annual-mean model surface temperatures agree within ±1.5 °C with climatological data, while the model tends to overestimate precipitation by 10-20mmmonth-1. Simulated precipitation δ18O shows a southwest to northeast decreasing pattern. The simulated annual-mean and seasonal δ18O results are in overall good agreement with observations from 15 Russian stations of the Global Network of Isotopes in Precipitation between 1970 and 2009. Annual-mean model results and measurements are highly correlated (r ² ~ 0.95) with a root mean square deviation of ±1‰. The model reproduces the seasonal variability of δ18O, which parallels the seasonal cycle of temperature, and the seasonal range from -25‰ in winter to -5‰ in summer. Analysing model results for the extended period 1960-2010, long-term increasing trends in temperature, precipitation and δ18O are detected in western Siberia. During the last 50 yr, winter temperatures have increased by 1.8 °C. Annual-mean precipitation rates have increased by 2-6mmmonth-1 50yr-1. Long-term trends of precipitation δ18O are also positive but at the detection limit (< 1‰ 50 yr-1). Regional climate is characterized by strong interannual variability, which in winter is strongly related to the North Atlantic Oscillation. In ECHAM5-wiso, regional temperature is the predominant factor controlling δ18O variations on interannual to decadal time scales with slopes of about 0.5‰ °C-1. Focusing on Kourovka, the simulated evolution of temperature, δ18O and, to a smaller extent, precipitation during the last fifty years is synchronous with model results averaged over entire western Siberia, suggesting that this site will be representative to monitor future isotopic changes this region. [ABSTRACT FROM AUTHOR]

Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on the northeast saddle of Mt. Qomolangma (Everest) (28°01' N, 86°58' E, 6518 m above sea level) give access to a tentative record of past Himalayan atmospheric mixing ratio of CH4 spanning the past 1200 yr. The major part of the record is affected by artifacts probably due to in situ production. After selecting what may represent the true atmospheric mixing ratio, an average of 749±25 ppbv of CH4 is estimated for the late preindustrial Holocene, which is ~36±17 (~73±18) ppbv higher than the atmospheric levels recorded in the Greenland (Antarctic) ice cores. A comparison of these new data with model simulations of the CH4 latitudinal gradient suggests either that the models do not get a correct balance between high and low latitude CH4 sources, or that the filtered CH4 profile from the ER cores remains biased by small artifacts. [ABSTRACT FROM AUTHOR]

For about 50 yr, ice cores have provided a wealth of information about past climatic and environmental changes. Ice cores from Greenland, Antarctica and other glacier-covered regions now encompass a variety of time scales. However, the longer time scales (e.g. at least back to the Last Glacial period) are covered by deep ice cores, the number of which is still very limited: seven from Greenland, with only one providing an undisturbed record of a part of the last interglacial period, and a dozen from Antarctica, with the longest record covering the last 800 000 yr. This article aims to summarize this successful adventure initiated by a few pioneers and their teams and to review key scientific results by focusing on climate (in particular water isotopes) and climate-related (e.g. greenhouse gases) reconstructions. Future research is well taken into account by the four projects defined by IPICS. However, it remains a challenge to get an intact record of the Last Interglacial in Greenland and to extend the Antarctic record through the mid-Pleistocene transition, if possible back to 1.5 Ma. [ABSTRACT FROM AUTHOR]

We present here surface water vapor isotopic measurements conducted from June to August~2010 at the NEEM camp, NW-Greenland (77.45° N 51.05° W, 2484 m a.s.l.). Measurements were conducted at 9 different heights from 0.1 m to 13.5 m above the snow surface using two different types of cavity-enhanced near infrared absorption spectroscopy analyzers. For each instrument specific protocols were developed for calibration and drift corrections. The inter-comparison of corrected results from different instruments reveals excellent reproducibility, stability, and precision with a standard deviation of ~ 0.23‰ for δ18O and ~ 1.4‰ for δD. Diurnal and intra-seasonal variations show strong relationships between changes in local surface humidity and water vapor isotopic composition, and with local and synoptic weather conditions. This variability probably results from the interplay between local moisture fluxes, linked with firn-air exchanges, boundary layer dynamics, and large-scale moisture advection. Particularly remarkable are several episodes characterized by high (> 40‰) surface water vapor deuterium excess. Air mass back-trajectory calculations from atmospheric analyses and water tagging in the LMDZiso atmospheric model reveal that these events are associated with predominant Arctic air mass origin. The analysis suggests that high deuterium excess levels are a result of strong kinetic fractionation during evaporation at the sea ice margin. [ABSTRACT FROM AUTHOR]

Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions.

Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores.

New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models. [ABSTRACT FROM AUTHOR]

Water stable isotopes provide integrated tracers of the atmospheric water cycle, affected by changes in air mass origin, non-convective and convective processes and continental recycling. Novel remote sensing and in situ measuring techniques have recently offered opportunities for monitoring atmospheric water vapour isotopic composition. Recently developed infrared laser spectrometers allow for continuous in situ measurements of surface water vapour δDv and δ18Ov. So far, very few intercomparison of measurements conducted using different techniques have been achieved at a given location, due to difficulties intrinsic to the comparison of integrated with local measurements. Nudged simulations conducted with high resolution isotopically enabled GCMs provide a consistent framework for comparison with the different types of observations. Here, we compare simulations conducted with the ECHAM5-wiso model with three types of water vapour isotopic data obtained during summer 2012 at the forest site of Kourovka, Western Siberia: daily mean GOSAT δDv soundings, hourly ground-based FTIR total atmospheric columnar δDv amounts, and in situ hourly Picarro δDv measurements. There is an excellent correlation between observed and predicted δDv at surface while the comparison between water column values derived from the model compares well with FTIR and GOSAT estimates. This research was supported by the grant of Russian government under the contract 11.G34.31.0064. [ABSTRACT FROM AUTHOR]

Correct estimate of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice cores studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: output of a firn densification model and measurements of δ15 N of N2 in air trapped in ice core. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available δ15 N measurements performed from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rate and temperature conditions. While firn densification simulations are able to correctly represent most of the δ15N trends over the last deglaciation measured in the EDC, BI, TALDICE and EDML ice cores, they systematically fail to capture BI and EDML δ15N glacial levels, a mismatch previously seen for Central East Antarctic ice cores. Using empirical constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka), we can rule out the existence of a large convective zone as the explanation of the glacial firn model- δ15N data mismatch for this site. The good match between modelled and measured δ15N at TALDICE as well as the lack of any clear correlation between insoluble dust concentration in snow and δ15N records in the different ice cores suggest that past changes in loads of impurities are not the only main driver of glacial-interglacial changes in firn lock-in depth. We conclude that firn densification dynamics may instead be driven mostly by accumulation rate changes. The mismatch between modelled and measured δ15N may be due to inaccurate reconstruction of past accumulation rate or underestimated influence of accumulation rate in firnification models. [ABSTRACT FROM AUTHOR]

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 102 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval that provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve to establish Antarctic Ice Core Chronology 2012, the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Lake Vostok, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. No significant phase difference is detected between the EDC and Vostok isotopic records, but depth shifts between the Vostok 3G and 5G ice cores prevent from looking at this problem accurately. Three possible candidates for the Toba volcanic super-eruption ∼73 kyr ago are suggested in the Vostok and EDC volcanic records. Neither the ECM, DEP nor the sulfate fingerprints for these 3 events are significantly larger than many others in the records. [ABSTRACT FROM AUTHOR]

We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. Observations allow direct and indirect estimate of Δdepth. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The bipolar seesaw antiphase relationship is generally supported by the ice-gas cross synchronisation between EDC and the GRIP, EDML and TALDICE ice cores, which provide support for method 4. Applying the bipolar seesaw hypothesis to the deeper section of the EDC core confirms that the ice flow is complex and can help improving our reconstruction of the thinning function and thus of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggested that it is due to an overestimation of the glacial Close Off Depth by the firn densification model. In contrast we find that the glaciological models probably underestimate the Δdepth during termination II. Finally, we show that method 2 based on 15N data produces for the last deglaciation a Δdepth estimate which is in good agreement with methods 3 and 4. [ABSTRACT FROM AUTHOR]

A single isotope ratio (δD or δ18O) of water is widely used as an air-temperature proxy in Antarctic ice cores. These isotope ratios, however, do not solely depend on airtemperature but also on the extent of distillation of heavy isotopes out of atmospheric water vapor from an oceanic moisture source to a precipitation site. The temperature changes at the oceanic moisture source (ΔTsource) and at the precipitation site (ΔTsite) can be retrieved by using deuterium-excess (d) data. A new d record from Dome Fuji, Antarctica is produced spanning the past 360 000 yr and compared with records from Vostok and EPICA Dome C ice cores. To retrieve ΔTsource and ΔTsite information, different linear regression equations have been proposed using theoretical isotope distillation models. A major source of uncertainty lies in the coefficient of regression, βsite which is related to the sensitivity of d to ΔTsite. We show that different ranges of temperature and selections of isotopic model outputs may increase the value of βsite by a factor of two. To explore the impacts of this coefficient on the reconstructed temperatures, we apply for the first time the exact same methodology to the isotope records from the three Antarctica ice cores. We show that uncertainties in the βsite coefficient strongly affect (i) the glacial-interglacial magnitude of ΔTsource; (ii) the imprint of obliquity in ΔTsource and in the site-source temperature gradient. By contrast, we highlight the robustness of ΔTsite reconstruction using water isotopes records. [ABSTRACT FROM AUTHOR]

We measured &dgr;17O and &dgr;18O in two Antarctic ice cores at EPICA Dome C (EDC) and TALDICE (TD), respectively, and computed 17O-excess with respect to VSMOW. The comparison of our 17O-excess data with the previous record obtained at Vostok (Landais et al., 2008a) revealed differences up to 35 ppm in 17O-excess mean level and evolution for the three sites. Our data show that the large increase depicted at Vostok (20 ppm) during the last deglaciation is a regional and not a general pattern in the temporal distribution of 17O-excess in East Antarctica. The EDC data display an increase of 12 ppm, whereas the TD data show no significant variation from the Last Glacial Maximum (LGM) to the Early Holocene (EH). A Lagrangian moisture source diagnostic revealed very different source regions for Vostok and EDC compared to TD. These findings combined with the results of a sensitivity analysis, using a Rayleigh-type isotopic model, suggest that normalized relative humidity (RHn) at the oceanic source region (OSR) is a determining factor for the spatial differences of 17O-excess in East Antarctica. However, 17O-excess in remote sites of continental Antarctica (e.g. Vostok) may be highly sensitive to local effects. Hence, we consider 17O-excess in coastal East Antarctic ice cores (TD) to be more reliable as a proxy for RHn at the OSR. [ABSTRACT FROM AUTHOR]

Based on a composite of several measurement series performed on ice samples stored at -25 °C or -50 °C, we present and discuss the first &dgr;O2/N2 record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at -25 °C show clear gas loss affecting the precision and mean level of the &dgr;O2/N2 record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off, and &dgr;O2/N2 in air bubbles, from which orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering, and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC. Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between &dgr;O2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the &dgr;O2/N2 record (and vice versa). Recognizing these limitations, we restrict the use of our &dgr;O2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300-800 ka period. [ABSTRACT FROM AUTHOR]

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 111 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval which provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve for the establishment of the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Vostok lake, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. A significant phase difference is detected between the EDC and Vostok isotopic records during the 95-120 kyr interval, but not during Termination II. Three possible candidates for the Toba volcanic super-eruption ∼73 kyr ago are suggested in the Vostok and EDC volcanic records. However the ECM, DEP and sulfate fingerprints for these three events are not significantly larger than many others in the records. [ABSTRACT FROM AUTHOR]

The sensitivity of interglacial Greenland temperature to orbital and CO2 forcing is investigated using the NorthGRIP ice core data and coupled ocean-atmosphere IPSL-CM4 model simulations. These simulations were conducted in response to different interglacial orbital configurations, and to increased CO2 concentrations. These different forcings cause very distinct simulated seasonal and latitudinal temperature and water cycle changes, limiting the analogies between the last interglacial and future climate. However, the IPSL-CM4 model shows similar magnitudes of Arctic summer warming and climate feedbacks in response to 2 x CO2 and orbital forcing of the last interglacial period (126 000 years ago). The IPSL-CM4 model produces a remarkably linear relationship between TOA incoming summer solar radiation and simulated changes in summer and annual mean central Greenland temperature. This contrasts with the stable isotope record from the Greenland ice cores, showing a multimillennial lagged response to summer insolation. During the early part of interglacials, the observed lags may be explained by ice sheet-ocean feedbacks linked with changes in ice sheet elevation and the impact of meltwater on ocean circulation, as investigated with sensitivity studies. A quantitative comparison between ice core data and climate simulations requires stability of the stable isotope - temperature relationship to be explored. Atmospheric simulations including water stable isotopes have been conducted with the LMDZiso model under different boundary conditions. This set of simulations allows calculation of a temporal Greenland isotope-temperature slope (0.3-0.4‰ per °C) during warmer-than-present Arctic climates, in response to increased CO2, increased ocean temperature and orbital forcing. This temporal slope appears half as large as the modern spatial gradient and is consistent with other ice core estimates. It may, however, be model-dependent, as indicated by preliminary comparison with other models. This suggests that further simulations and detailed inter-model comparisons are also likely to be of benefit. Comparisons with Greenland ice core stable isotope data reveals that IPSL-CM4/LMDZiso simulations strongly underestimate the amplitude of the ice core signal during the last interglacial, which could reach +8-10 °C at fixedelevation. While the model-data mismatch may result from missing positive feedbacks (e.g. vegetation), it could also be explained by a reduced elevation of the central Greenland ice sheet surface by 300-400 m. [ABSTRACT FROM AUTHOR]

Based on a composite of several measurement series performed on ice samples stored at -25°C or -50°C, we present and discuss the first δO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at -25°C show clear gas loss affecting the precision and mean level of the δO2/N2 record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off and δO2/N2 in air bubbles, from which an orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC to at least 2.5 kyrs (thousands of years). Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between δO2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO2/N2 record (and vice versa). Recognizing these limitations, we restrict the use of our δO2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyrs) over the 300-800 ka period. We illustrate the uncertainties associated with data quality, filtering and tuning target for periods of low eccentricity by highlighting the difficulty to constrain the duration of Marine Isotopic Stage 11 based on the EDC δO2/N2 information. [ABSTRACT FROM AUTHOR]

We measured δ17O and δ18O in two Antarctic ice cores at EPICA Dome C (EDC) and TALDICE (TD), respectively and computed 17O-excess with respect to VSMOW. The comparison of our 17O-excess data with the previous record obtained at Vostok (Landais et al., 2008) revealed differences up to 35 ppm in 17O-excess mean level and evolution for the three sites. Our data showed that the large increase depicted at Vostok (20 ppm) during the last deglaciation, is a regional and not a general pattern in the temporal distribution of 17O-excess in East Antarctica. The EDC data display an increase of 13 ppm, whereas the TD data show no significant variation from the Last Glacial Maximum (LGM) to the Early Holocene (EH). Lagrangian moisture source diagnostic revealed very different source regions for Vostok and EDC compared to TD. These findings combined with the results of a sensitivity analysis, using a Rayleigh-type isotopic model, suggest that relative humidity (RH) at the oceanic source region (OSR) are a determining factor for the spatial differences of 17O-excess in East Antarctica. However, 17O-excess in remote sites of continental Antarctica (e.g. Vostok) may be highly sensitive to local effects. Hence, we consider 17O-excess in coastal East Antarctic ice cores (TD) to be more reliable as a proxy for RH at the OSR. [ABSTRACT FROM AUTHOR]

The sensitivity of interglacial Greenland temperature to orbital and CO2 forcing is investigated using the NorthGRIP ice core data and coupled ocean-atmosphere IPSL-CM4 model simulations. These simulations were conducted in response to different interglacial orbital configurations, and to increased CO2 concentrations. These different forcings cause very distinct simulated seasonal and latitudinal temperature and water cycle changes, limiting the analogies between the last interglacial and future climate. However, the IPSL-CM4 model shows similar magnitudes of Arctic summer warming and climate feedbacks in response to 2xCO2 and orbital forcing of the last interglacial period (126 000 yr ago). The IPSL model produces a remarkably linear relationship between top of atmosphere incoming summer solar radiation and simulated changes in summer and annual mean central Greenland temperature. This contrasts with the stable isotope record from the Greenland ice cores, showing a multi-millennial lagged response to summer insolation. During the early part of interglacials, the observed lags may be explained by ice sheet-ocean feedbacks linked with changes in ice sheet elevation and the impact of meltwater on ocean circulation, as investigated with sensitivity studies. A quantitative comparison between ice core data and climate simulations requires to explore the stability of the stable isotope -- temperature relationship. Atmospheric simulations including water stable isotopes have been conducted with the LMDZiso model under different boundary conditions. This set of simulations allows to calculate a temporal Greenland isotope-temperature slope (0.3-0.4‰ per °C) during warmer than present Arctic climates, in response to increased CO2, increased ocean temperature and orbital forcing. This temporal slope appears twice as small as the modern spatial gradient and is consistent with other ice core estimates. A preliminary comparison with other model results implies that other mechanisms could also play a role. This suggests that further simulations and detailed inter-model comparisons are also likely to be of benefit. [ABSTRACT FROM AUTHOR]

We expand here the description of the Antarctic temperature variability during the long interglacial period occurring ∼400 thousand years before the present (Marine Isotopic Stage, MIS 11). Our study is based on new detailed deuterium measurements conducted on the EPICA Dome C ice core, Antarctica, with a ∼50 year temporal resolution. Despite an ice diffusion of a length reaching ∼8 cm at MIS 11 depth, the data allow us to highlight a variability at multicentennial scale for MIS 11, as it has already been observed for the Holocene period (MIS 1). The differences between MIS 1 and MIS 11 are analysed regarding the links between multi-millennial trends and sub-millennial variability. The EPICA Dome C deuterium record shows an increased variability and the onset of millennial to sub-millennial periodicities at the beginning of the final cooling phase of MIS 11. Our findings are robust with respect to sensitivity tests on the somewhat uncertain MIS 11 duration. [ABSTRACT FROM AUTHOR]

A new, decadally resolved record of the 10Be peak at 41 kyr from the EPICA Dome C ice core (Antarctica) is used to match it with the same peak in the GRIP ice core (Greenland). This permits a direct synchronisation of the climatic variations around this time period, independent of uncertainties related to the ice age-gas age difference in ice cores. Dansgaard-Oeschger event 10 is in the period of best synchronisation and is found to be coeval with an Antarctic temperature maximum. Simulations using a thermal bipolar seesaw model agree reasonably well with the observed relative climate chronology in these two cores. They also reproduce three Antarctic warming events observed between AI and A2. [ABSTRACT FROM AUTHOR]

The EPICA (European Project for Ice Coring in Antarctica) Dome C drilling in East Antarctica has now been completed to a depth of 3260 m, at only a few meters above bedrock. Here we present the new EDC3 chronology, which is based on the use of 1) a snow accumulation and mechanical flow model, and 2) a set of independent age markers along the core. These are obtained by pattern matching of recorded parameters to either absolutely dated paleoclimatic records, or to insolation variations. We show that this new time scale is in excellent agreement with the Dome Fuji and Vostok ice core time scales back to 100 kyr within 1 kyr. Discrepancies larger than 3 kyr arise during MIS 5.4, 5.5 and 6, which points to anomalies in either snow accumulation or mechanical flow during these time periods. We estimate that EDC3 gives accurate event durations within 20% (2δ) back to MIS 11 and accurate absolute ages with a maximum uncertainty of 6 kyr back to 800 kyr. [ABSTRACT FROM AUTHOR]

While there are no indications of mixing back to 800 000 years in the EPICA Dome C ice core record, comparison with marine sediment records shows significant differences in the timing and duration of events prior to stage 11 (∼430ka, thousands of years before 1950). A relationship between the isotopic composition of atmospheric oxygen (δ18O of O2, noted δ18Oatm) and daily northern hemisphere summer insolation has been observed for the youngest four climate cycles. Here we use this relationship with new δ18O of O2 measurements to show that anomalous flow in the bottom 500 m of the core distorts the duration of events by up to a factor of 2. By tuning δ18Oatm to orbital precession we derive a corrected thinning function and present a revised age scale for the interval corresponding to Marine Isotope Stages 11-20 in the EPICA Dome C ice core. Uncertainty in the phasing of δ18Oatm with respect to insolation variations in the precession band limits the accuracy of this new agescale to ±6 kyr (thousand of years). The previously reported ∼ 30 kyr duration of interglacial stage 11 is unchanged. In contrast, the duration of stage 15.1 is reduced by a factor of 2, from 31 to 16 kyr. [ABSTRACT FROM AUTHOR]

One-dimensional (1-D) ice flow models are used to construct the age scales at the Dome C and Dome Fuji drilling sites (East Antarctica). The poorly constrained glaciological parameters at each site are recovered by fitting independent age markers identified within each core. We reconstruct past accumulation rates, that are larger than those modelled using the classical vapour saturation pressure relationship during glacial periods by up to a factor 1.5. During the Early Holocene, changes in reconstructed accumulation are not linearly related to changes in ice isotopic composition. A simple model of past elevation changes is developed and shows an amplitude variation of 110-120m at both sites. We suggest that there is basal melting at Dome C (0.56±0.19 mm/yr). The reconstructed velocity profile is highly non-linear at both sites, which suggests complex ice flow effects. This induces a non-linear thinning function in both drilling sites, which is also characterized by bumps corresponding to variations in ice thickness with time. [ABSTRACT FROM AUTHOR]

While there are no indications of mixing back to 800 000 years in the EPICA Dome C ice core record, comparison with marine sediment records shows significant differences in the timing and duration of events prior to stage 11 (∼430 ka, thousand of years before 1950). A relationship between the isotopic composition of atmospheric oxygen (δ18O of O2, noted δ18Oatm) and daily northern hemisphere summer insolation has been observed for the youngest four climate cycles. Here we use this relationship with new δ18O of O2 measurements to show that anomalous flow in the bottom 500m of the core distorts the duration of events by up to a factor of 2. By tuning ∼18Oatm to orbital precession we derive a corrected thinning function and present a revised age scale for the interval corresponding to Marine Isotope Stages 11-20 in the EPICA Dome C ice core. Uncertainty in the phasing of δ18Oatm with respect to insolation variations in the precession band limits the accuracy of this new agescale to ±6 kyr (thousand of years). The previously reported ∼30 kyr duration of interglacial stage 11 is unchanged. In contrast, the duration of stage 15.1 is reduced by a factor of 2, from 31 to 16 kyr. [ABSTRACT FROM AUTHOR]

1-D ice flow models are used to construct the age scales at the Dome C and Dome Fuji drilling sites (East Antarctica). The poorly constrained glaciological parameters at each sites are recovered by fitting independent age markers identified on each core. We construct past accumulation rates, that are larger than those modeled using the classical vapour saturation pressure relationship during glacial periods by up to a factor 1.5. During the Early Holocence, changes in reconstructed accumulation are not linearly related to changes in ice isotopic composition. A simple model of past elevation changes is developed and shows and amplitude variation of 110-120 m at both sites. We suggest that there is basal melting at Dome C (0.56±0.19 mm/yr). The reconstructed velocity profile is highly non linear at both sites, which suggests complex ice flow effects. This induces a non linear thinning function in both drilling sites, which is also characterized by bumps corresponding to variations in surface elevation with time. [ABSTRACT FROM AUTHOR]

Two Himalayan ice cores display a factor-two decreasing trend of air content over the past two millennia, in contrast to the relatively stable values in Greenland and Antarctica ice cores over the same period. Because the air content can be related with the relative frequency and intensity of melt phenomena, its variations along the Himalayan ice cores provide an indication of summer temperature trend. Our reconstruction point toward an unprecedented warming trend in the 20th century but does not depict the usual trends associated with "Medieval Warm Period" (MWP), or "Little Ice Age" (LIA). [ABSTRACT FROM AUTHOR]

Ice cores provide unique archives of past climate and environmental changes based only on physical processes. Quantitative temperature reconstructions are essential for the comparison between ice core records and climate models. Several methods have been developed to reconstruct past local temperatures from deep ice cores. Here we first analyse the long term fluctuations of temperature as depicted in the long Antarctic record from EPICA Dome C. The long term imprint of obliquity changes in the EPICA Dome C record is highlighted and compared to simulations conducted with the ECBILT-CLIO intermediate complexity climate model. We discuss the comparison between the current interglacial period and the long interglacial corresponding to marine isotopic stage 11, ∼400 kyr BP. Previous studies had focused on the role of precession and the thresholds required to induce glacial inceptions. We suggest that, due to the low eccentricity configuration of MIS 11 and the Holocene, the effect of precession on the incoming solar radiation is damped and that changes in obliquity must be taken into account. The EPICA Dome C alignment of terminations I and VI published in 2004 corresponds to a phasing of the obliquity signals. A conjunction of low obliquity and minimum northern hemisphere summer insolation is not found in the next tens of thousand years, supporting the idea of an unusually long interglacial ahead. As a second point relevant for future climate change, we discuss the magnitude and rate of change of past temperatures reconstructed from Greenland (NorthGRIP) and Antarctic (Dome C) ice cores. Past episodes of temperatures above the present-day values by up to 5°C are recorded at both locations during the penultimate interglacial period. The polar warming simulated by coupled climate models forced by a CO2increase of 1% per year is compared to ice-core-based temperature reconstructions. In Antarctica, the CO2-induced warming lies clearly beyond the natural rhythm of temperature fluctuations. In Greenland, the CO2-induced warming is as fast or faster than the most rapid temperature shifts of the last ice age. The magnitude of polar temperature change in response to a quadrupling of atmospheric CO2 is comparable to the magnitude of the polar temperature change from the Last Glacial Maximum to present-day. When forced by prescribed changes in ice sheet reconstructions and CO2 changes, climate models systematically underestimate the glacial-interglacial polar temperature change. [ABSTRACT FROM AUTHOR]

Two Himalayan ice cores display a factor-two decreasing trend of air content over the past two millennia, in contrast to the relatively stable values in Greenland and Antarctica ice cores over the same period. Because the air content can be related with the relative frequency and intensity of melt phenomena, its variations along the Himalayan ice cores provide an indication of summer temperature trend. Our reconstruction point toward an unprecedented warming trend in the 20th century but does not depict the usual trends associated with "Medieval Warm Period" (MWP), or "Little Ice Age" (LIA). [ABSTRACT FROM AUTHOR]