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Recent studies have suggested that water isotopologues in snow pits from remote East Antarctica can be influenced by the input of stratospheric water, which has anomalously high 17O‐excess values. However, it remains unclear whether the 17O‐excess records preserved in snow and ice from this region can be used to reconstruct stratosphere‐troposphere exchange (STE). In this study, we present high‐resolution 17O‐excess records from two snow pits at Dome A, the highest point of the Antarctic ice sheet. The 17O‐excess records show a significant positive correlation with the strength of the Brewer‐Dobson circulation (BDC), the hemispheric‐scale troposphere‐stratosphere overturn circulation. Stronger BDC leads to more stratospheric water input over Antarctica and higher 17O‐excess, and vice versa. In addition, the 17O‐excess records also have a significant positive correlation with the Southern Annular Mode (SAM) index, because SAM modulates Antarctic precipitation, which has a dilution effect on the stratospheric water input. The 17O‐excess records do not show significant correlations with local temperature and relative humidity in the moisture source region. These results suggest the dominant effect of BDC on 17O‐excess and indicate the potential for using 17O‐excess records in ice cores from remote sites in East Antarctica for reconstructing long‐term variations of STE, and understanding their mechanisms and climate effects. Plain Language Summary: Previous studies suggest the influence of stratospheric water on 17O‐excess variations in snow pits from the inland Ppateau of East Antarctica, and the potential for using ice‐core 17O‐excess to trace historical stratosphere‐troposphere exchange. However, it remains unclear whether ice‐core 17O‐excess records from this remote part of East Antarctica can be used as a proxy for stratosphere‐troposphere exchange. In this study, we presented high‐resolution 17O‐excess records from two snow pits at Dome A, the highest point of the Antarctic ice sheet. We found that the 17O‐excess variations over the past several decades were mainly controlled by the strength of the Brewer‐Dobson circulation. This discovery could open up an opportunity for new methods to reconstruct long‐term variations of the Brewer‐Dobson circulation. Key Points: The 17O‐excess records in snow pits at Dome A show a significant correlation with the strength of the Brewer‐Dobson circulation (BDC)Stronger BDC leads to more stratospheric water input over Antarctica and higher 17O‐excess, and vice versaThe 17O‐excess records are also significantly correlated with the Southern Annular Mode, which dilutes the stratospheric water input [ABSTRACT FROM AUTHOR]

In central Antarctica, where accumulation rates are very low, summer sublimation of surface snow is a key element of the surface mass balance, but its fingerprint in isotopic composition of water (δD, δ18O, and δ17O) remains unclear. In this study, we examined the influence of summer sublimation on δD, δ18O, and δ17O in precipitation using data sets of isotopic composition of precipitation at various sites on the inland East Antarctica. We found unexpectedly low δ18O values in the summer precipitation, decoupled from surface air temperatures. This feature can be explained by the combined effects of weak or nonexistent temperature inversion and moisture recycling associated with sublimation‐condensation processes in summer. Isotopic fractionation during the moisture‐recycling process also explains the observed high values of d‐excess and 17O‐excess in summer precipitation. Our results suggest that the local cycle of sublimation‐condensation in summer is an important process for the isotopic composition of surface snow, water vapor, and consequently precipitation on inland East Antarctica. Key Points: Isotopic composition in summer precipitation on inland East Antarctica is more depleted than expected from the range of surface air temperatures during precipitationThe strong depletion of isotopic composition in summer precipitation are caused by the combined effects of weak or nonexistent temperature inversion and moisture recycling associated with snow sublimationIsotopic fractionation occurs during the moisture recycling process [ABSTRACT FROM AUTHOR]

Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands 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 different 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 and 160 ka) and the oldest part (340-800 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 some site-specific δO2/N2 variations. Such an observation, the evidence of a 100 ka periodicity in the δO2/N2 signal and the difficulty to identify extrema and mid-slopes in δO2/N2 increase the uncertainty associated with the use of δO2/N2 as an orbital tuning tool, now calculated to be 3-4 ka. When combining records of δ18Oatm and δO2/N2 from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (~ 400 ka, ~ 720-800 ka). Our data set reveals a time-varying offset between δO2/N2 and δ18Oatm records over the last 800 ka that we interpret as variations in the lagged response of δ18Oatm to precession. The largest offsets are identified during Terminations II, MIS 8 and MIS 16, corresponding to periods of destabilization of the Northern polar ice sheets. We therefore suggest that the occurrence of Heinrich-like events influences the response of δ18Oatm to precession. [ABSTRACT FROM AUTHOR]

The spatial and temporal variability of snow accumulation near Dome Argus, Antarctica, is assessed using new snow pit and stake measurement data together with existing snow pit, ice core and automatic weather station records. Snow accumulation rate shows large inter-annual variations, but stable multi-decadal levels over the last seven centuries. Spatial variations in snow accumulation within the space of 50 km of Dome Argus are relatively small, probably thanks to the smooth topography. A comparison of theses accumulation observations with ECMWF reanalyses (ERA-40 and ERA-Interim) suggests ECMWF reanalysis captures the seasonal variations, but underestimates the overall snow accumulation at Dome Argus by ~50 %. The moisture sources for precipitation over Dome Argus are examined by means of a Lagrangian moisture source diagnostic, based on the tracing of specific humidity changes along air parcel trajectories, for the period 2000-2004 using operational ECMWF analysis data. Dome Argus mainly receives moisture from the mid-latitude (46 ± 4°S) South Indian Ocean, with a seasonal latitudinal shift of about 6°. Compared to other central East Antarctic deep ice core sites such as Dome F, Dome C, Vostok, and EPICA Dronning Maud Land, Dome Argus has a more southerly moisture origin, probably due to topographic influences on the moisture transport paths. These results have important implications for the interpretation of future ice cores at Dome Argus. [ABSTRACT FROM AUTHOR]

Abstract: After the success of EPICA, the European Project for Ice coring in Antarctica which, at Dome C (East Antarctica) has provided access to climate and environmental records covering the last 800 ka (thousands of years), the ice core community is now engaged in the challenge to obtain older records. Obtaining a 1.5 million year (Ma) record of climate and greenhouse gases is one of the priorities of the International Partnerships in Ice Core Sciences (IPICS) largely motivated by the yet unexplained shift in climate cyclicity around the Mid-Pleistocene transition (MPT) around 1.2 Ma ago. From EPICA results and recently published articles, we further examine how such a 1.5 Ma old ice core will help, and is indeed indispensable, to depict and understand this transition. [ABSTRACT FROM AUTHOR]

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 1000years for central Antarctic sites. Here we explore the possibility that δ15N of N2 is a gas phase proxy of climate, which can be used to synchronize gas and ice records. We present the δ15N record from the EPICA Dome C (EDC) ice core covering the last three glacial terminations and five glacial‐interglacial cycles between 300 and 800ka. Previous studies have shown that gravitational settling enriches δ15N 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 δ15N during glacial periods, and a negative correlation with temperature. Instead, EDC δ15N 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 δ15N and ice deuterium content. The tightest correlation is observed over glacial terminations, supporting the idea that δ15N is a property in the gas phase that records changes in surface conditions linked to deglacial warming. [Copyright &y& Elsevier]

Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. Here we present results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data and the present work, we find that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. We report the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172–300 p.p.m.v. [ABSTRACT FROM AUTHOR]

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 insolation, 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. [ABSTRACT FROM AUTHOR]

Abstract: Quaternary climate and atmospheric composition: new ice cores. Over the last 20 years, studies of Antarctic and Greenland ice cores have provided a wealth of information directly relevant to the past and to the future evolution of our climate with, as more important, the discovery of a link between greenhouse gases and climate in the past and the characterization of rapid climate changes. These results are based on the analysis of deep ice cores such as the one drilled at the Vostok site, which allows us to describe the evolution of Antarctic climate and of atmospheric composition over 420 ka (thousands of years), and GRIP and GISP2 (Greenland), which precisely depict the rhythm of rapid changes during the last 100 ka. Information available from ice cores has considerably increased in 2004 thanks to the EPICA Dome C ice core in Antarctica and to the North GRIP one, in Greenland. We present these two successful international programs and describe the first results they have provided, with the EPICA Dome C core covering eight climatic cycles (800 ka) and the North GRIP one allowing us to reach, for the first time from a northern-hemisphere ice core, the Eemian, the warmest past of the last interglacial around 120 ka ago. To cite this article: J. Jouzel, C. R. Palevol 5 (2006) . [Copyright &y& Elsevier]

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long-28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future. [ABSTRACT FROM AUTHOR]

Past isotopic composition of atmospheric oxygen (δ18Oatm) can be inferred from the analysis of air bubbles trapped in ice caps. The longest record covers the last 420 ka (thousand of years) at the Vostok site in East Antarctica. It shows a strong modulation by the precession and striking similarities, but also noticeable differences, with the deep-sea core oxygen 18 record from which changes in the oxygen content of sea-water (δ18Osw) and in sea-level can be derived. Indeed, δ18Oatm is driven by complex fractionation processes occuring during respiration and photosynthesis. Both δ18Oatm and its difference with respect to δ18Osw (the Dole effect) are influenced by factors such as the ratio of oceanic and terrestrial productivities which may have significantly changed between different climates. Also, the response time of δ18Oatm to oceanic changes should be taken in consideration but this parameter itself depends on biospheric activity. We review the various aspects of the link between the δ18Oatm and the δ18Osw signals. We also examine the approach followed by Shackleton (Science (2000)) for deriving sea-level change from the δ18Oatm Vostok record, assuming that the phase between this record and insolation changes is constant and that the Dole effect is a fraction of the precessional component of the δ18Oatm signal. Glaciological constraints on the Vostok chronology and the complexity of the Dole effect show that those two assumptions are quite probably too simplistic. [Copyright &y& Elsevier]

The analysis of air bubbles from ice cores has yielded a precise record of atmospheric greenhouse gas concentrations, but the timing of changes in these gases with respect to temperature is not accurately known because of uncertainty in the gas age—ice age difference. We have measured the isotopic composition of argon in air bubbles in the Vostok core during Termination III (∼240,000 years before the present). This record most likely reflects the temperature and accumulation change, although the mechanism remains unclear. The sequence of events during Termination III suggests that the CO[sub2] increase lagged Antarctic deglacial warming by 800 ± 200 years and preceded the Northern Hemisphere deglaciation. [ABSTRACT FROM AUTHOR]

Each glacial – interglacial transition of the Quaternary occurs in a different orbital context leading to various timing for the deglaciation and sequence of high vs low latitudes events. Termination 3, 250 kyears before present (ka), is an unusual deglaciation in the context of the last 9 deglaciations recorded in the old EPICA Dome C (EDC) Antarctic ice core: it exhibits a three-phase sequence, two warming phases separated by a small cooling, the last phase suggesting a particularly rapid temperature increase. We present here new high resolution δ15N and deuterium excess (d-excess) data from the EDC ice core to provide a detailed temperature change estimate during this termination. Then, we combined the δD and δ18O to discuss the relationship between high and low latitude changes through the d-excess. We also provide the high vs low latitude sequence of events over this deglaciation without chronological uncertainty using low latitude ice core proxies. In agreement with previous studies based on speleothem analyses, we show that the first phase of Termination 3 (256–249 ka) is associated with small Heinrich like events linked to changes in ITCZ position, monsoon activity and teleconnections with Antarctica. In a context of minimum Northern Hemisphere insolation, this leads to a rather strong Antarctic warming, as observed in the δ15N record in contrast to the relatively small δD increase. The second warming phase occurs during the rise of the Northern hemisphere insolation, with a large Heinrich like event leading to the characteristic Antarctic warming observed in the δ15N and δD increase as for the more recent terminations. • New high resolution δ 15N and d-excess measurements over Termination 3 provide a quantification of temperature evolution over this period. • Three-phase high vs low latitude sequence of events over Termination 3 in a context of enhanced millennial scale variability. • Impurity contents does not play a major role on the δ 15N evolution over deglaciations. [ABSTRACT FROM AUTHOR]

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 17 O-excess measurements in surface snow and especially for remote regions characterized by low temperature and accumulation rate. In this study, we present new 17 O-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 17 O-excess data significantly decrease inland, with a latitudinal gradient of − 1.33 ± 0.41 per meg/degree, an altitudinal gradient of − 0.48 ± 0.17 per meg / 100 m , and a temperature gradient of 0.35 ± 0.11 per meg / °C . 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 17 O-excess in Antarctic precipitation cannot only be explained by temperature at condensation and/or influences of relative humidity in the moisture source region. [ABSTRACT FROM AUTHOR]

Abstract: Using the most recent compilation of surface Antarctic snow isotopic composition data and a 1km 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 δ 18O data, 92.7% of the observed δD 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 δ 18O, δD and deuterium excess to better use in many hydrological and paleoclimate applications. [Copyright &y& Elsevier]

Abstract: Tritium concentration was measured in snow deposited at the GRIP site (central Greenland) and at the Vostok station (east Antarctica) from snow pits covering the period 1980–1990. The objective of the study was to investigate tritium concentrations in polar regions several decades after the bomb peak of the sixties and to put them in the context of available data for environmental tritium in the Arctic and the Antarctic over the last five decades. The tritium content of the samples was measured by mass spectrometry using the helium-3 regrowth method. In Antarctica, the tritium concentrations are in the range 70–110 TU. The comparison of the bomb tritium history at different locations show that tritium levels increase moving inland, where vapour pressure becomes extremely low and therefore more sensitive to the intrusion of stratospheric air masses highly enriched in tritium. Although most tritium fallout occurred in the Northern hemisphere, the tritium levels in central Greenland in the 80''s, in the range 10–40 TU, are significantly lower than at Vostok. Unlike Antarctica, no such continental effect is observed in Greenland, due to the higher water vapour content of the air masses, as evidenced by the much higher snow accumulation rate. Whereas tritium fallout in Antarctica appears to occur as a result of direct injections of stratospheric tritium during winter, Arctic fallout are the result of the dominant spring injection of stratospheric air at mid-latitude, in line with the deposition of other stratospheric tracers. [Copyright &y& Elsevier]

A record of atmospheric carbon dioxide (CO[sub 2]) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO[sub 2] record back to 650,000 years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO[sub 2] lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO[sub 2] remains stable throughout the six glacial cycles, suggesting that the relationship between CO[sub 2] and Antarctic climate remained rather constant over this interval. [ABSTRACT FROM AUTHOR]

The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH[sub 4]) and nitrous oxide (N[sub 2]O) back to 650,000 years before the present. A combined record of CH[sub 4] measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 ± 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH[sub 4] concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N[sub 2]O record shows maximum concentrations of 278 = 7 ppbv, slightly higher than early Holocene values. [ABSTRACT FROM AUTHOR]

Abstract: Typical rapid climate events punctuating the last glacial period in Greenland, Europe and Antarctica are compared to two rapid events occurring under warmer conditions: (i) Dansgaard–Oeschger event 25, the first abrupt warming occurring during last glacial inception; (ii) 8.2 ka BP event, the only rapid cooling recorded during the Holocene in Greenland ice cores and in Ammersee, Germany. The rate of warming during previous warmer interglacial periods is estimated from polar ice cores to 1.5 °C per millennium, without abrupt changes. Climate change expected for the 21st century should however be at least 10 times faster. To cite this article: V. Masson-Delmotte et al., C. R. Geoscience 337 (2005). [Copyright &y& Elsevier]

Reports the occurrence of an Oceanic Cold Reversal during the last deglaciation. Measurement of a detailed deuterium excess profile along the Dome C European Project for Ice Coring in Antarctic core; Incidence of an Oceanic Cold Reversal following the Antarctic Cold Reversal; Similarities of results taken in Antarctica and in Dome C base.