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Barbante C, Fischer H, Masson-Delmotte V, Waelbroeck C, Wolff EW, . (2010). Climate of the last million years: new insights from EPICA and other records
. Quat Sci Rev, 29(1-2), 1–7.
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Capron E, Landais A, Lemieux-Dudon B, Schilt A, Masson-Delmotte V, Buiron D, Chappellaz J, Dahl-Jensen D, Johnsen S, Leuenberger M, Loulergue L, Oerter H, . (2010). Synchronising EDML and NorthGRIP ice cores using δ18O of atmospheric oxygen (δ18Oatm) and CH4 measurements over MIS5 (80-123 kyr)
. Quat Sci Rev, 29(1-2), 222–234.
Abstract: Water isotope records from the EPICA Dronning Maud Land (EDML) and the NorthGRIP ice cores have revealed a one to one coupling between Antarctic Isotope Maxima (AIM) and Greenland Dansgaard-Oeschger (DO) events back to 50 kyr. In order to explore if this north–south coupling is persistent over Marine Isotopic Stage 5 (MIS 5), a common timescale must first be constructed.
Here, we present new records of δ18O of O2 (δ18Oatm) and methane (CH4) measured in the air trapped in ice from the EDML (68–147 kyr) and NorthGRIP (70–123 kyr) ice cores. We demonstrate that, through the period of interest, CH4 records alone are not sufficient to construct a common gas timescale between the two cores. Millennial-scale variations of δ18Oatm are evidenced over MIS 5 both on the Antarctic and Greenland ice cores and are coupled to CH4 profiles to synchronise the NorthGRIP and EDML records. They are shown to be a precious tool for ice core synchronisation.
With this new dating strategy, we produce the first continuous and accurate sequence of the north–south climatic dynamics on a common ice timescale for the last glacial inception and the first DO events of MIS 5, reducing relative dating uncertainties to an accuracy of a few centuries at the onset of DO events 24 to 20. This EDML-NorthGRIP synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period. The relationship between Antarctic warming amplitudes and their concurrent Greenland stadial duration highlights the particularity of DO event 21 and its Antarctic counterpart. Our results suggest a smaller Southern Ocean warming rate for this long DO event compared to DO events of MIS 3.
Programme: 458
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Masson-Delmotte V, Stenni B, Pol K, Braconnot P, Cattani O, Falourd S, Kageyama M, Jouzel J, Landais A, Minster B, Barnola J M, Chappellaz J, Krinner G, Johnsen S, Rothlisberger R, Hansen J, Mikolajewicz U, Otto-Bliesner B, . (2010). EPICA Dome C record of glacial and interglacial intensities
. Quat Sci Rev, 29(1-2), 113–128.
Abstract: Climate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800 000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile. The consistency between stable isotope-derived temperature and other environmental and climatic proxies measured along the EDC ice core is analysed at the orbital scale and compared with estimates of global ice volume. MIS 2,12 and 16 appear as the strongest glacial maxima, while MIS 5.5 and 11 appear as the warmest interglacial maxima. The links between EDC temperature, global temperature, local and global radiative forcings are analysed. We show: (i) a strong but changing link between EDC temperature and greenhouse gas global radiative forcing in the first and second part of the record; (ii) a large residual signature of obliquity in EDC temperature with a 5 ky lag; (iii) the exceptional character of temperature variations within interglacial periods. Focusing on MIS 5.5, the warmest interglacial of EDC record, we show that orbitally forced coupled climate models only Simulate a precession-induced shift of the Antarctic seasonal cycle of temperature. While they do capture annually persistent Greenland warmth, models fail to capture the warming indicated by Antarctic ice core delta D. We suggest that the model-data mismatch may result from the lack of feedbacks between ice sheets and climate including both local Antarctic effects due to changes in ice sheet topography and global effects due to meltwater-thermohaline circulation interplays. An MIS 5.5 sensitivity study conducted with interactive Greenland melt indeed induces a slight Antarctic warming. We suggest that interglacial EDC optima are caused by transient heat transport redistribution comparable with glacial north-south seesaw abrupt climatic changes. (C) 2009 Elsevier Ltd. All rights reserved.
Keywords: glaciology, meteorology climatology,
Programme: 458
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Dreyfus Gabrielle B, Jouzel Jean, Bender Michael L, Landais Amalle, Masson-Delmotte Valrie, Leuenberger Markus, . (2010). Firn processes and δ15N: potential for a gas-phase climate proxy
. Quat Sci Rev, 29(1-2), 28–42.
Abstract: In order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores, we must accurately account for the age difference between ice and gas at a given depth. This gas age-ice age difference depends on the age of the ice at the bottom of the firn layer, where the bubbles are closed-off. Firn densification models are used to calculate how this age difference varied in the past, but have an uncertainty on the order of 1000 years for central Antarctic sites. Here we explore the possibility that 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[hyphen (true graphic)]interglacial cycles between 300 and 800 ka. 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.
Programme: 458
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Köhler Peter, Bintanja Richard, Fischer Hubertus, Joos Fortunat, Knutti Reto, Lohmann Gerrit, Masson-Delmotte Valérie, . (2010). What caused Earth's temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity
. Quat Sci Rev, 29(1-2), 129–145.
Abstract: The temperature on Earth varied largely in the Pleistocene from cold glacials to interglacials of different warmths. To contribute to an understanding of the underlying causes of these changes we compile various environmental records (and model-based interpretations of some of them) in order to calculate the direct effect of various processes on Earth's radiative budget and, thus, on global annual mean surface temperature over the last 800,000 years. The importance of orbital variations, of the greenhouse gases CO 2 , CH 4 and N 2 O, of the albedo of land ice sheets, annual mean snow cover, sea ice area and vegetation, and of the radiative perturbation of mineral dust in the atmosphere are investigated. Altogether we can explain with these processes a global cooling of 3.90.8K in the equilibrium temperature for the Last Glacial Maximum (LGM) directly from the radiative budget using only the Planck feedback that parameterises the direct effect on the radiative balance, but neglecting other feedbacks such as water vapour, cloud cover, and lapse rate. The unaccounted feedbacks and related uncertainties would, if taken at present day feedback strengths, decrease the global temperature at the LGM by 8.01.6K. Increased Antarctic temperatures during the Marine Isotope Stages 5.5, 7.5, 9.3 and 11.3 are in our conceptual approach difficult to explain. If compared with other studies, such as PMIP2, this gives supporting evidence that the feedbacks themselves are not constant, but depend in their strength on the mean climate state. The best estimate and uncertainty for our reconstructed radiative forcing and LGM cooling support a present day equilibrium climate sensitivity (excluding the ice sheet and vegetation components) between 1.4 and 5.2K, with a most likely value near 2.4K, somewhat smaller than other methods but consistent with the consensus range of 24.5K derived from other lines of evidence. Climate sensitivities above 6K are difficult to reconcile with Last Glacial Maximum reconstructions.
Programme: 458
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Landais A, Dreyfus G, Capron E, Masson-Delmotte V, Sanchez-Goi MF, Desprat S, Hoffmann G, Jouzel J, Leuenberger M, Johnsen S, . (2010). What drives the millennial and orbital variations of δ18Oatm?
. Quat Sci Rev, 29(1-2), 235–246.
Abstract: The isotopic composition of atmospheric oxygen (δ18Oatm) 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 δ18Oatm to date ice core records. However, the drivers of these δ18Oatm 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 δ18Oatm variations. We show that, superimposed on the dominant precession signal, millennial δ18Oatm variations record systematic decreases during warm phases of the Dansgaard-Oeschger events and systematic increases during the cold phases.
Programme: 458
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Lourantou A, Chappellaz J, Barnola J-M, Masson-Delmotte V, Raynaud D, . (2010). Changes in atmospheric CO2 and its carbon isotopic ratio during the penultimate deglaciation
. Quat Sci Rev, 29(17-18), 1983–1992.
Abstract: The largest natural increases in atmospheric CO2 concentration as recorded in ice cores occur when the Earth climate abruptly shifts from a glacial to an interglacial state. Open questions remain regarding the processes at play, the sequences of events and their similarities along different glacial-interglacial transitions. Here we provide new combined data of atmospheric CO2 and its carbon isotopic ratio (δ13CO2) for the penultimate glacial-interglacial transition (Termination II) from the Antarctic EPICA Dome C ice core. Together with the strongest Antarctic warming, this transition bears the largest CO2 increase (104 ppmv) of the last nine Terminations, ending with an overshoot of 21 ppmv occurring within ~300 y and leading to higher levels than those of the late pre-industrial Holocene. The full CO2 rise is accompanied by an overall decrease of the δ13CO2 minimum values, on which three positive excursions are superimposed. Peak-to-peak δ13CO2 changes in our record can reach ~1[per mille sign]. The ice core atmospheric δ13CO2 appears more depleted by ~0.2[per mille sign] during Termination II compared to Termination I, paralleling a similar carbon isotopic depletion recorded in marine data. During both terminations, most of CO2 and δ13CO2 variations are attributed to southern ocean stratification breakdown and decreased efficiency of the biological pump. Compared to Termination I, Termination II ice core data point to different timings of decrease in iron supply and sea-ice extent, suggesting that they could account for distinct patterns of the carbon cycle.
Programme: 458
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Stenni B, Masson-Delmotte V, Selmo E, Oerter H, Meyer H, Rthlisberger R, Jouzel J, Cattani O, Falourd S, Fischer H, Hoffmann G, Iacumin P, Johnsen SJ, Minster B, Udisti R, . (2010). The deuterium excess records of EPICA Dome C and Dronning Maud Land ice cores (East Antarctica)
. Quat Sci Rev, 29(1-2), 146–159.
Abstract: New high-resolution deuterium excess (d) data from the two EPICA ice cores drilled in Dronning Maud Land (EDML) and Dome C (EDC) are presented here. The main moisture sources for precipitation at EDC and EDML are located in the Indian Ocean and Atlantic Ocean, respectively. The more southward moisture origin for EDML is reflected in a lower present-day d value, compared to EDC. The EDML and EDC isotopic records (δ18O and d) show the main climate features common to the East Antarctic plateau and similar millennial scale climate variability during the last glacial period. However, quite large δ18O and d differences are observed during MIS5.5 and the glacial inception with a long-term behaviour. A possibility for this long-term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models. Regional climate anomalies between the two sites during MIS5.5 could also be consistent with the observed EDML-EDC δ18O and d gradient anomalies. Simulations performed with the General Circulation Model ECHAM4 for different time slices provide a temporal temperature/isotope slope for the EDML region in fair agreement to the modern spatial slope. Tsite and Tsource records are extracted from both ice cores, using a modelling approach, after corrections for past δ18O seawater and elevation changes. A limited impact of d on Antarctic temperature reconstruction at both EDML and EDC has been found with a higher impact only at glacial inception. The AIM (Antarctic Isotope Maximum) events in both ice cores are visible also after the source correction, suggesting that these are real climate features of the glacial period. The different shape of the AIM events between EDC and EDML, as well as some climate features in the early Holocene, points to a slightly different climate evolution at regional scale. A comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssCa fluxes with Antarctic temperatures during glacial period and a tighter coupling of δ18O and Tsite with ssNa flux at EDML compared to EDC during the glacial period and MIS5.5.
Programme: 458
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Bentley Michael J, Ó Cofaigh Colm, Anderson John B, Conway Howard, Davies Bethan, Graham Alastair GC, Hillenbrand Claus-Dieter, Hodgson Dominic A, Jamieson Stewart SR, Larter Robert D, Mackintosh Andrew, Smith James A, Verleyen Elie, Ackert Robert P, Bart Philip J, Berg Sonja, Brunstein Daniel, Canals Miquel, Colhoun Eric A, Crosta Xavier, Dickens William A, Domack Eugene, Dowdeswell Julian A, Dunbar Robert, Ehrmann Werner, Evans Jeffrey, Favier Vincent, Fink David, Fogwill Christopher J, Glasser Neil F, Gohl Karsten, Golledge Nicholas R, Goodwin Ian, Gore Damian B, Greenwood Sarah L, Hall Brenda L, Hall Kevin, Hedding David W, Hein Andrew S, Hocking Emma P, Jakobsson Martin, Johnson Joanne S, Jomelli Vincent, Jones R Selwyn, Klages Johann P, Kristoffersen Yngve, Kuhn Gerhard, Leventer Amy, Licht Kathy, Lilly Katherine, Lindow Julia, Livingstone Stephen J, Massé Guillaume, McGlone Matt S, McKay Robert M, Melles Martin, Miura Hideki, Mulvaney Robert, Nel Werner, Nitsche Frank O, O'Brien Philip E, Post Alexandra L, Roberts Stephen J, Saunders Krystyna M, Selkirk Patricia M, Simms Alexander R, Spiegel Cornelia, Stolldorf Travis D, Sugden David E, van der Putten Nathalie, van Ommen Tas, Verfaillie Deborah, Vyverman Wim, Wagner Bernd, White Duanne A, Witus Alexandra E, Zwartz Dan, . (2014). A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
. Quat Sci Rev, 100, 1–9.
Abstract: A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
Keywords: Antarctic Ice Sheet, Glacial geology, Modelling, Quaternary,
Programme: 1048
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Hodgson Dominic A, Graham Alastair GC, Roberts Stephen J, Bentley Michael J, Cofaigh Colm Ó, Verleyen Elie, Vyverman Wim, Jomelli Vincent, Favier Vincent, Brunstein Daniel, Verfaillie Deborah, Colhoun Eric A, Saunders Krystyna M, Selkirk Patricia M, Mackintosh Andrew, Hedding David W, Nel Werner, Hall Kevin, McGlone Matt S, Van der Putten Nathalie, Dickens William A, Smith James A, . (2014). Terrestrial and submarine evidence for the extent and timing of the Last Glacial Maximum and the onset of deglaciation on the maritime-Antarctic and sub-Antarctic islands
. Quat Sci Rev, 100, 137–158.
Abstract: This paper is the maritime and sub–Antarctic contribution to the Scientific Committee for Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) community Antarctic Ice Sheet reconstruction. The overarching aim for all sectors of Antarctica was to reconstruct the Last Glacial Maximum (LGM) ice sheet extent and thickness, and map the subsequent deglaciation in a series of 5000 year time slices. However, our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub–Antarctic sector. Therefore, in this paper we focus on an assessment of the terrestrial and offshore evidence for the LGM ice extent, establishing minimum ages for the onset of deglaciation, and separating evidence of deglaciation from LGM limits from those associated with later Holocene glacier fluctuations. Evidence included geomorphological descriptions of glacial landscapes, radiocarbon dated basal peat and lake sediment deposits, cosmogenic isotope ages of glacial features and molecular biological data. We propose a classification of the glacial history of the maritime and sub–Antarctic islands based on this assembled evidence. These include: (Type I) islands which accumulated little or no LGM ice; (Type II) islands with a limited LGM ice extent but evidence of extensive earlier continental shelf glaciations; (Type III) seamounts and volcanoes unlikely to have accumulated significant LGM ice cover; (Type IV) islands on shallow shelves with both terrestrial and submarine evidence of LGM (and/or earlier) ice expansion; (Type V) Islands north of the Antarctic Polar Front with terrestrial evidence of LGM ice expansion; and (Type VI) islands with no data. Finally, we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme.
Keywords: Antarctic ice sheet, Sub-Antarctica, Maritime Antarctica glaciation, Deglaciation, Quaternary, Climate,
Programme: 1048
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