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Climate dependent contrast in surface mass balance in East Antarctica over the past 216 kyr
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Documenting past changes in the East Antarctic surface mass balance is important to improve ice core chronologies and to constrain the ice sheet contribution to global mean sea level. Here we reconstruct the past changes in the ratio of surface mass balance (SMB ratio) between the EPICA Dome C (EDC) and Dome Fuji (DF) East Antarctica ice core sites, based on a precise volcanic synchronisation of the two ice cores and on corrections for the vertical thinning of layers. During the past 216 000 years, this SMB ratio, denoted SMBEDC/SMBDF, varied between 0.7 and 1.1, decreasing during cold periods and increasing during warm periods. While past climatic changes have been depicted as homogeneous along the East Antarctic Plateau, our results reveal larger amplitudes of changes in SMB at EDC compared to DF, consistent with previous results showing larger amplitudes of changes in water stable isotopes and estimated surface temperature at EDC compared to DF. Within interglacial periods and during the last glacial inception (Marine Isotope Stages, MIS-5c and MIS-5d), the SMB ratio deviates by up to 30% from what is expected based on differences in water stable isotope records. Moreover, the SMB ratio is constant throughout the late parts of the current and last interglacial periods, despite contrasting isotopic trends. These SMB ratio changes not closely related to isotopic changes are one of the possible causes of the observed gaps between the ice core chronologies at DF and EDC. Such changes in SMB ratio may have been caused by (i) climatic processes related to changes in air mass trajectories and local climate, (ii) glaciological processes associated with relative elevation changes, or (iii) a combination of climatic and glaciological processes, such as the interaction between changes in accumulation and in the position of the domes. Our inferred SMB ratio history has important implications for ice sheet modeling (for which SMB is a boundary condition) or atmospheric modeling (our inferred SMB ratio could serve as a test).
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... Les enregistrements des 4 carottes de glace EDC, Vostok, TALDICE et EDML sont directement comparables sur la même échelle d'âge AICC2012. Les autres carottes (Taylor Dome, Dome F) n'ont pas encore été intégrées dans une datation cohérente des carottes de glace même s'il a déjà été mis en évidence des différences de l'ordre de quelques milliers d'années entre les datations pour le dernier interglaciaire pour les carottes de EDC et de Dome F (Parrenin et al., 2015a ;Fujita et al., 2015 ;Bazin et al., 2015). Les enregistrements issus des isotopes de l'eau en Antarctique indiquent que la dernière période interglaciaire commence par un optimum climatique associé à des valeurs en d 18 O significativement plus hautes que le niveau de d 18 O actuel : + 1.8 à + 3.8 ‰ à TALDICE et Dome F respectivement. ...
Unique results have been obtained from ice core research over the last 40 years documenting the evolution of polar temperature and atmospheric composition at millennial and orbital timescales over the last 800 000 years. Recent progresses on coherent ice core dating integrated stratigraphic markers as well as a bayesian method. This led to an easy compilation of various ice core records. Moreover, new measurements in polar ice cores and dating improvements enabled one to quantify the phasing between temperature and CO2 concentration in atmosphere. Initial rises in CO2 concentration and Antarctic temperature are synchronous over the last two deglaciations within ± 200 years. High resolution measurements in ice cores and efforts in relative dating between Greenland and Antarctic have led to an accurate description of the millennial variability of the last glacial period: in addition to the bipolar seesaw mechanism, a regional climate variability has been evidenced in Antarctica. Finally, ice cores are also very useful to document the ice sheet – climate system in a warmer world. Recent reconstructions inferred from Greenland ice cores indeed suggest that the temperature of the last interglacial was 8°C warmer than today in Greenland.
The recovery of a new Antarctic ice core spanning the past ∼ 1.5 million years will advance our understanding of climate system dynamics during the Quaternary. Recently, glaciological field surveys have been conducted to select the most suitable core location near Dome Fuji (DF), Antarctica. Specifically, ground-based radar-echo soundings have been used to acquire highly detailed images of bedrock topography and internal ice layers. In this study, we use a one-dimensional (1-D) ice-flow model to compute the temporal evolutions of age and temperature, in which the ice flow is linked with not only transient climate forcing associated with past glacial–interglacial cycles but also transient basal melting diagnosed along the evolving temperature profile. We investigated the influence of ice thickness, accumulation rate, and geothermal heat flux on the age and temperature profiles. The model was constrained by the observed temperature and age profiles reconstructed from the DF ice-core analysis. The results of sensitivity experiments indicate that ice thickness is the most crucial parameter influencing the computed age of the ice because it is critical to the history of basal temperature and basal melting, which can eliminate old ice. The 1-D model was applied to a 54 km long transect in the vicinity of DF and compared with radargram data. We found that the basal age of the ice is mostly controlled by the local ice thickness, demonstrating the importance of high-spatial-resolution surveys of bedrock topography for selecting ice-core drilling sites.
Unique results have been obtained from ice core research over the last 40 years documenting the evolution of polar temperature and atmospheric composition at millennial and orbital timescales over the last 800 000 years. Recent progresses on coherent ice core dating integrated stratigraphie markers as well as a Bayesian method. This led to an easy compilation of various ice core records. Moreover, new measurements in polar ice cores and dating improvements enabled one to quantify the phasing between temperature and CO2 concentration in atmosphere. Initial rises in CO2 concentration and Antarctic temperature are synchronous over the last two deglaciations within ± 200 years. High resolution measurements in ice cores and efforts in relative dating between Greenland and Antarctic have led to an accurate description of the millennial variability of the last glacial period: in addition to the bipolar seesaw mechanism, a regional climate variability has been evidenced in Antarctica. Finally, ice cores are also very useful to document the ice sheet - climate system in a warmer world. Recent reconstructions inferred from Greenland ice cores indeed suggest that the temperature of the last interglacial was 8°C warmer than today in Greenland.
Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were synchronized to better understand their chronology. A total of 1401 volcanic tie points were identified covering the past 216 kyr. DFO2006, the chronology for the DF core characterized by strong constraining by the O2/N2 age markers, was compared with AICC2012, the chronology for 5 cores including the EDC core, and characterized by glaciological approaches combining ice flow modelling with various age markers. The age gaps between the two chronologies are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of the gap of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, ratios of duration DFO2006/AICC2012 are 85% at a period from the late stage of MIS 6 to MIS 5d and 114% at a period from MIS 5d to 5b. We then compared the DFO2006 with another chronology of the DF core, DFGT2006, characterized by glaciological approaches with weaker constraining by age markers. Features of the DFO2006/DFGT2006 age gaps are very similar to those of the DFO2006/AICC2012 age gaps. This fact lead us to hypothesize that a cause of the systematic DFO2006/AICC2012 age gaps at MIS 5 are associated with differences in the dating approaches. Besides, ages of speleothem records from China agreed well with DFO2006 at MIS 5c and 5d but not at MIS 5b. Thus, we hypothesize at least at MIS 5c and 5d, major sources of the gaps are systematic errors in surface mass balance estimation in the glaciological approach. Compatibility of the age markers should be carefully assessed in future.
No abstract available.
doi:10.2204/iodp.sd.5.05.2007
Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were synchronized to better understand their chronology. A total of 1401 volcanic tie points were identified covering the past 216 kyr. DFO2006, the chronology for the DF core characterized by strong constraining by the O2/N2 age markers, was compared with AICC2012, the chronology for 5 cores including the EDC core, and characterized by glaciological approaches combining ice flow modelling with various age markers. The age gaps between the two chronologies are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of the gap of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, ratios of duration DFO2006/AICC2012 are 85% at a period from the late stage of MIS 6 to MIS 5d and 114% at a period from MIS 5d to 5b. We then compared the DFO2006 with another chronology of the DF core, DFGT2006, characterized by glaciological approaches with weaker constraining by age markers. Features of the DFO2006/DFGT2006 age gaps are very similar to those of the DFO2006/AICC2012 age gaps. This fact lead us to hypothesize that a cause of the systematic DFO2006/AICC2012 age gaps at MIS 5 are associated with differences in the dating approaches. Besides, ages of speleothem records from China agreed well with DFO2006 at MIS 5c and 5d but not at MIS 5b. Thus, we hypothesize at least at MIS 5c and 5d, major sources of the gaps are systematic errors in surface mass balance estimation in the glaciological approach. Compatibility of the age markers should be carefully assessed in future.
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 mechan-ical 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. Dis-crepancies 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% (2σ) back to MIS11 and accurate absolute ages with a maximum uncer-tainty of 6 kyr back to 800 kyr.
The study of the distribution of crystallographic orientations (i.e., the fabric) along ice cores provides information on past and current ice flow in ice-sheets. Besides the usually observed formation of a vertical single maximum fabric, the EPICA Dome C ice core (EDC) shows an abrupt and unexpected strengthening of its fabric during termination II around 1750 m depth. Such strengthening has already been observed for sites located on an ice-sheet flank. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the effective viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in effective viscosity and investigate its implication for ice flow and dating.
The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to sev-eral thousand years (ka) exist between ice cores over the last climatic cycle. In this context, we are hereby introduc-ing the Antarctic Ice Core Chronology 2012 (AICC2012), a new and coherent timescale developed for four Antarctic ice cores, namely Vostok, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML) and Talos Dome (TALDICE), alongside the Greenlandic NGRIP record. The AICC2012 timescale has been constructed using the Bayesian tool Dat-ice (Lemieux-Dudon et al., 2010) that combines glaciolog-ical inputs and data constraints, including a wide range of relative and absolute gas and ice stratigraphic markers. We focus here on the last 120 ka, whereas the companion paper by Bazin et al. (2013) focuses on the interval 120–800 ka. Compared to previous timescales, AICC2012 presents an improved timing for the last glacial inception, respecting the glaciological constraints of all analyzed records. Moreover, with the addition of numerous new stratigraphic markers and improved calculation of the lock-in depth (LID) based on δ 15 N data employed as the Datice background scenario, the AICC2012 presents a slightly improved timing for the bipo-lar sequence of events over Marine Isotope Stage 3 associ-ated with the seesaw mechanism, with maximum differences of about 600 yr with respect to the previous Datice-derived chronology of Lemieux-Dudon et al. (2010), hereafter de-noted LD2010. Our improved scenario confirms the regional differences for the millennial scale variability over the last glacial period: while the EDC isotopic record (events of tri-angular shape) displays peaks roughly at the same time as the NGRIP abrupt isotopic increases, the EDML isotopic record (events characterized by broader peaks or even extended pe-riods of high isotope values) reached the isotopic maximum several centuries before. It is expected that the future contribution of both other long ice core records and other types of chronological constraints to the Datice tool will lead to further refinements in the ice core chronologies beyond the AICC2012 chronology. For the time being however, we recommend that AICC2012 be used as the preferred chronology for the Vostok, EDC, EDML and TALDICE ice core records, both over the last glacial cycle Published by Copernicus Publications on behalf of the European Geosciences Union. 1734 D. Veres et al.: The Antarctic ice core chronology (AICC2012) (this study), and beyond (following Bazin et al., 2013). The ages for NGRIP in AICC2012 are virtually identical to those of GICC05 for the last 60.2 ka, whereas the ages beyond are independent of those in GICC05modelext (as in the construc-tion of AICC2012, the GICC05modelext was included only via the background scenarios and not as age markers). As such, where issues of phasing between Antarctic records in-cluded in AICC2012 and NGRIP are involved, the NGRIP ages in AICC2012 should therefore be taken to avoid in-troducing false offsets. However for issues involving only Greenland ice cores, there is not yet a strong basis to rec-ommend superseding GICC05modelext as the recommended age scale for Greenland ice cores.
An accurate and coherent chronological frame-work is essential for the interpretation of climatic and envi-ronmental records obtained from deep polar ice cores. Un-til now, one common ice core age scale had been devel-oped based on an inverse dating method (Datice), combin-ing glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thou-sands of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2013), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120–800 ka. In this framework, new measurements of δ 18 O atm over Marine Isotope Stage (MIS) 11–12 on EDC and a complete δ 18 O atm record of the TALDICE ice cores permit us to derive additional or-bital gas age constraints. The coherency of the different orbitally deduced ages (from δ 18 O atm , δO 2 /N 2 and air con-tent) has been verified before implementation in AICC2012. The new chronology is now independent of other archives and shows only small differences, most of the time within the original uncertainty range calculated by Datice, when compared with the previous ice core reference age scale EDC3, the Dome F chronology, or using a comparison be-tween speleothems and methane. For instance, the largest de-viation between AICC2012 and EDC3 (5.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.
Determination of the surface and bed topography at Dome C, East Antarctica - Volume 44 Issue 146 - Ignazio Ezio Tabacco, Andrea Passerini, Filippo Corbelli, Michael Gorman
[1] We present a 5.3- Myr stack ( the " LR04'' stack) of benthic delta(18)O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm. This is the first benthic delta(18)O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene. We also present a new LR04 age model for the Pliocene- Pleistocene derived from tuning the delta(18)O stack to a simple ice model based on 21 June insolation at 65degreesN. Stacked sedimentation rates provide additional age model constraints to prevent overtuning. Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 5.3 Myr and in the precession band for more than half of the record. The LR04 stack contains significantly more variance in benthic delta(18) O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic. Finally, the relative phases of the stack's 41- and 23- kyr components suggest that the precession component of delta(18)O from 2.7 - 1.6 Ma is primarily a deep- water temperature signal and that the phase of delta(18)O precession response changed suddenly at 1.6 Ma.
Changes in ice discharge from Antarctica constitute the largest uncertainty in future sea-level projections, mainly because of the unknown response of its marine basins(1). Most of West Antarctica's marine ice sheet lies on an inland-sloping bed(2) and is thereby prone to a marine ice sheet instability(3-5). A similar topographic configuration is found in large parts of East Antarctica, which holds marine ice equivalent to 19 m of global sea-level rise(6), that is, more than five times that of West Antarctica. Within East Antarctica, the Wilkes Basin holds the largest volume of marine ice that is fully connected by subglacial troughs. This ice body was significantly reduced during the Pliocene epoch(7). Strong melting underneath adjacent ice shelves with similar bathymetry(8) indicates the ice sheet's sensitivity to climatic perturbations. The stability of the Wilkes marine ice sheet has not been the subject of any comprehensive assessment of future sea level. Using recently improved topographic data(6) in combination with ice-dynamic simulations, we show here that the removal of a specific coastal ice volume equivalent to less than 80 mm of global sea-level rise at the margin of the Wilkes Basin destabilizes the regional ice flow and leads to a self-sustained discharge of the entire basin and a global sea-level rise of 3-4 m. Our results are robust with respect to variation in ice parameters, forcing details and model resolution as well as increased surface mass balance, indicating that East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century.