TALDICE (TALos Dome Ice CorE) is a 1620 m deep ice core drilled at Talos Dome, an ice dome located at the edge of the East Antarctic Plateau in the Ross Sea Sector. The Antarctic Ice Core Common ...Chronology (AICC2012) extended the age scale of the core until ∼150 ka (1438 m depth) (Bazin et al., 2013), while no age scale was available below 1438 m depth.
In this work we present the new TALDICE-deep1 chronology using the new measurements of δ18Oatm, δD and 81Kr as well as the inverse model IceChrono1.
The TALDICE-deep1 chronology stops at 1548 m, as the portion below this depth is probably affected by mixing processes. The new age scale extends the climate record for the Ross Sea Sector of the East Antarctic Ice Sheet back to MIS 10.1–343 ka (1548 m depth) and identifies both MIS 7 and 9 warm stages, which show specificities in the δD signal. However, it is not possible to recover the isotopic record beyond stage 10.1 as the signal shows a quasi-flat shape. Thereby, the new chronology TADICE-deep1 doubles the extension of the previous age scale as it covers the three past glacial/interglacial cycles.
•Multi-approach and multi-proxy data set provided a new age scale for the deep portion of the TALDICE ice core.•Two additional glacial-interglacial cycles identified in the extremely thinned deep part of the TALDICE ice core.•First application of the krypton dating technique to define an ice core age scale.•Anomalous water stable isotope signals during past warm periods from an East Antarctic peripheral ice core.
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.
The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to several thousand years (ka) exist ...between ice cores over the last climatic cycle. In this context, we are hereby introducing 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 Datice (Lemieux-Dudon et al., 2010) that combines glaciological 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 δ15N data employed as the Datice background scenario, the AICC2012 presents a slightly improved timing for the bipolar sequence of events over Marine Isotope Stage 3 associated 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 denoted 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 triangular 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 periods 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 (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 construction 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 included in AICC2012 and NGRIP are involved, the NGRIP ages in AICC2012 should therefore be taken to avoid introducing false offsets. However for issues involving only Greenland ice cores, there is not yet a strong basis to recommend superseding GICC05modelext as the recommended age scale for Greenland ice cores.
The Last Interglacial (LIG) represents an invaluable case study to investigate the response of components of the Earth system to global warming. However, the scarcity of absolute age constraints in ...most archives leads to extensive use of various stratigraphic alignments to different reference chronologies. This feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the LIG. Here, we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span (∼140–100 ka) encompassing the penultimate deglaciation, the LIG and the glacial inception. Climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described. Quantitative estimates of the associated absolute and relative age uncertainties are provided.
Recommendations are subsequently formulated on how best to define absolute and relative chronologies. Future climato-stratigraphic alignments should provide (1) a clear statement of climate hypotheses involved, (2) a detailed understanding of environmental parameters controlling selected tracers and (3) a careful evaluation of the synchronicity of aligned paleoclimatic records. We underscore the need to (1) systematically report quantitative estimates of relative and absolute age uncertainties, (2) assess the coherence of chronologies when comparing different records, and (3) integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations.
Finally, we provide a sequence of major climatic events with associated age uncertainties for the period 140–105 ka, which should serve as a new benchmark to disentangle mechanisms of the Earth system's response to orbital forcing and evaluate transient climate simulations.
•Review of methods to date climatic archives across the Last Interglacial (LIG).•Careful evaluation of climate hypotheses underlying record alignment methods.•Systematic and quantitative estimates of age uncertainties.•First sequence of events with age uncertainties between 140 and 105 ka.•The lack of LIG age markers limits studies of LIG millennial-scale variability.
Human occupation in Europe strongly fluctuated over the Quaternary. Archaeological records suggest an intermittent human occupation in Western Europe between 900 and 500 ka, especially in the north ...of Europe at latitude higher than 45°N. On the opposite, southern Europe, more stable from a palaeoenvironmental point of view, was occupied continuously. This period is followed by a more widespread and dense occupation over the last 450 ka. In parallel, the last 900 ka are characterized by global climatic oscillations and display shifts between glacial/drier and interglacial/wetter periods that modulate the general repartition of fauna and flora. The pacing of these climatic periods is well recorded in numerous palaeoclimatic archives that provide global as well as regional information concerning past climatic and environmental changes. A transition is observed from 1.25 Ma until up to 450 ka (Mid-Pleistocene Revolution) with a change of the dominant periodicity of climate cycles from 41ka to 100 ka in the absence of substantial change in orbital forcing. After 450 ka, the amplitude between glacials and interglacials increases. The change in periodicity since 450 ka corresponds to a change in the density of human occupations as well as the Acheulean technoculture expansion in Europe. There is a general perception that these climatic and environmental oscillations have played a role in human occupation and his morphological evolution. For instance, temperate environments might have favored permanent occupations or occupations over larger territories with long periods dominated by dry meadows and steppes and followed by the expansion of broadleaf deciduous and confireous forests. Testing this hypothesis for the period encompassing 900 to 500 ka is a challenge because of the lack of a common chronological framework between climatic/environmental archives and sites of human occupation, but also because archaeological records are only snapshots of cultural and morphological changes of hominins.
Deep ice core chronologies have been improved over the past years through the addition of new age constraints. However, dating methods are still associated with large uncertainties for ice cores from ...the East Antarctic plateau where layer counting is not possible. Indeed, an uncertainty up to 6 ka is associated with AICC2012 chronology of EPICA Dome C (EDC) ice core, which mostly arises from uncertainty on the delay between changes recorded in δ18Oatm and in June 21st insolation variations at 65°N used for ice core orbital dating. Consequently, we need to enhance the knowledge of this delay to improve ice core chronologies.
We present new high-resolution EDC δ18Oatm record (153–374 ka) and δO2/N2 measurements (163–332 ka) performed on well-stored ice to provide continuous records of δ18Oatm and δO2/N2 between 100 and 800 ka. The comparison of δ18Oatm with the δ18Ocalcite from East Asian speleothems shows that both signals present similar orbital and millennial variabilities, which may represent shifts in the InterTropical Convergence Zone position, themselves associated with Heinrich events. We thus propose to use the δ18Ocalcite as target for δ18Oatm orbital dating. Such a tuning method improves the ice core chronology of the last glacial inception compared to AICC2012 by reconciling NGRIP and mid-latitude climatic records. It is especially marked during Dansgaard-Oeschger 25 where the proposed chronology is 2.2 ka older than AICC2012. This δ18Oatm – δ18Ocalcite alignment method applied between 100 and 640 ka improves the EDC ice core chronology, especially over MIS 11, and leads to lower ice age uncertainties compared to AICC2012.
•Complete EPICA Dome C δ18Oatm and δO2/N2 records between 100 and 800 ka.•δ18Oatm link to insolation is modulated by occurrence of millennial events.•Links between δ18Oatm and δ18Ocalcite can be used to improve ice core chronology.
Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and ...environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg–Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice–air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.
Afin d’étudier les variations climatiques enregistrées par les carottes de glace, il est nécessaire d’avoir des datations précises à la fois pour les phases gaz et glace. Le but de ce travail de ...thèse a été d’améliorer les chronologies des carottes de glace, couvrant les derniers 800 000 ans, au travers de nouvelles mesures de la composition isotopique de l’air (δ15N, δ18Oatm et δO2/N2) piégé dans la glace d’EPICA Dôme C (EDC) et de l’utilisation de l’outil de datation "Datice". Le premier résultat important de cette thèse a été la production de la chronologie cohérente pour les carottes de glace ("Antarctic Ice Core Chronology", AICC2012) pour EDC, Vostok, EPICA Droning Maud Land (EDML), TALos Dôme ICE core (TALDICE) et NorthGRIP. Sur cette nouvelle chronologie la théorie du see-saw bipolaire reste valable. AICC2012 donne un âge pour la Terminaison II en accord avec les autres archives climatiques. De plus, les durées des périodes interglaciaires restent inchangées par rapport à la chronologie EDC3. Lors de la construction d’AICC2012 nous avons mis en évidence plusieurs points nécessitant des améliorations. Nous avons donc procédé à l’amélioration de Datice dans le but d’intégrer correctement les contraintes issues du comptage des couches annuelles et leurs erreurs. Ces améliorations conduisent à des chronologies cohérentes tout en respectant les hypothèses sous-jacentes à Datice. Nous proposons aussi une nouvelle formulation de l’erreur associée à la fonction d’amincissement à partir de l’analyse des propriétés mécaniques de la glace dans le cas d’EDC. Pour finir, les nouvelles mesures du δO2/N2 et du δ18Oatm effectuées sur de la glace bien conservée d’EDC nous ont permis de définir de nouvelles contraintes d’âge. La comparaison de ces traceurs mesurés à Vostok, EDC et Dôme F sur le MIS 5 a permis de mettre en évidence une possible influence de paramètres climatiques locaux sur le δO2/N2. L’analyse du retard entre le δ18Oatm et la précession sur les derniers 800 ka montre des variations de ce dernier. Nous suggérons que ce retard est augmenté par l’occurence d’évènements de Heinrich à certaines périodes. Les résultats de cette thèse sont à prendre en compte pour le prochain exercice de datation cohérente pour les carottes de glace.
In order to study the climate variations recorded by ice cores, it is necessary to have precise chronologies for the ice and gas phases. The aim of this work has been to improve ice cores chronologies, covering the last 800 000 years, through new measurements of the isotopic composition of the air δ15N, δ18Oatm et δO2/N2) trapped in EPICA Dome C (EDC) ice core and the use of the Datice dating tool.The first important result of this PhD has been the production of the Antarctic Ice Core Chronology (AICC2012), common for EDC, Vostok, EPICA Droning Maud Land (EDML), TALos Dome ICE core (TALDICE) and NorthGRIP ice cores. The bipolar see-saw theory is still valid on the new chronology. The AICC2012 chronology gives an age for Termination II in good agreement with other climate archives. Moreover, the duration of interglacial periods is unchanged compared to EDC3. While building the AICC2012 chronology, we have pointed out several limitations. Since then, we have improved Datice in order to correctly integrate constraints deduced from layer counting and their associated uncertainties. These improvements permit to build coherent chronologies respecting the underlying hypotheses of Datice. Moreover, we propose a new parameterization of the uncertainty associated with the background thinning function based on ice mechanical properties of EDC ice core. Finally, we were able to deduce new age constraints thanks to the new measurements of δO2/N2 and δ18Oatm performed on well-conserved ice from EDC. A multi-proxy comparison of Vostok, EDC and Dome F ice cores over MIS 5 has highlighted a possible influence of local climatic parameters on δO2/N2. The analysis of the delay between δ18Oatm and precession shows some variability over the last 800 ka. We propose that the delay between δ18Oatm and precession is increased during periods associated with Heinrich events. The results obtained during this PhD should be used for the next ice core coherent chronology.
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