scholarly journals IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores

2014 ◽  
Vol 7 (5) ◽  
pp. 6811-6844
Author(s):  
F. Parrenin
Keyword(s):  
Probabilistic Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Air Bubbles ◽  
Ice Flow ◽  
Orbital Parameters ◽  
Information Depth ◽  
Dating Methods ◽  
Lock In

Abstract. Polar ice cores provides exceptional archives of past environmental conditions. Dating ice and air bubbles/hydrates in ice cores is complicated since it involves different dating methods: modeling of the sedimentation process (accumulation of snow at surface, densification of snow into ice with air trapping and ice flow), use of dated horizons by comparison to other well dated targets (other dated paleo-archives or calculated variations of Earth's orbital parameters), use of dated depth intervals, use of Δdepth information (depth shift between synchronous events in the ice matrix and its air/hydrate content), use of stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air links). Here I propose IceChrono v1, a new probabilistic model to combine these different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its confidence interval. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. IceChrono is similar in scope to the Datice model, but has differences on the mathematical, numerical and programming point of views. I apply IceChrono on two dating experiments. The first one is similar to the AICC2012 experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. The second experiment involves only the Berkner ice core in Antarctica and I produce the first dating of this ice core. IceChrono v1 is freely available under the GPL v3 open source license.

scholarly journals IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

2015 ◽  
Vol 8 (5) ◽  
pp. 1473-1492 ◽  
Author(s):  
F. Parrenin ◽  
L. Bazin ◽  
E. Capron ◽  
A. Landais ◽  
B. Lemieux-Dudon ◽  
...  
Keyword(s):  
Probabilistic Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Complex Problem ◽  
Polar Ice ◽  
Ice Flow ◽  
Marquardt Algorithm ◽  
Lock In

Abstract. 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.

scholarly journals Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2013 ◽  
Vol 9 (3) ◽  
pp. 983-999 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Last Deglaciation ◽  
Depth Study ◽  
Dronning Maud Land ◽  
The Last Deglaciation ◽  
Correct Estimation ◽  
Lock In

Abstract. 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.

scholarly journals Post-bubble close-off fractionation of gases in polar firn and ice cores: effects of accumulation rate on permeation through overloading pressure

2015 ◽  
Vol 15 (24) ◽  
pp. 13895-13914 ◽  
Author(s):  
T. Kobashi ◽  
T. Ikeda-Fukazawa ◽  
M. Suwa ◽  
J. Schwander ◽  
T. Kameda ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Accumulation Rate ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Significant Negative Correlation ◽  
Orbital Parameters ◽  
The Past ◽  
Pressure Sensitive ◽  
Core Project

Abstract. Gases in ice cores are invaluable archives of past environmental changes (e.g., the past atmosphere). However, gas fractionation processes after bubble closure in the firn are poorly understood, although increasing evidence indicates preferential leakages of smaller molecules (e.g., neon, oxygen, and argon) from the closed bubbles through the ice matrix. These fractionation processes are believed to be responsible for the observed millennial δO2/N2 variations in ice cores, linking ice core chronologies with orbital parameters. In this study, we investigated high-resolution δAr/N2 of the GISP2 (Greenland Ice Sheet Project 2), NGRIP (North Greenland Ice Core Project), and Dome Fuji ice cores for the past few thousand years. We find that δAr/N2 at multidecadal resolution on the "gas-age scale" in the GISP2 ice core has a significant negative correlation with accumulation rate and a positive correlation with air contents over the past 6000 years, indicating that changes in overloading pressure induced δAr/N2 fractionation in the firn. Furthermore, the GISP2 temperature and accumulation rate for the last 4000 years have nearly equal effects on δAr/N2 with sensitivities of 0.72 ± 0.1 ‰ °C−1 and −0.58 ± 0.09 ‰ (0.01 m ice year−1)−1, respectively. To understand the fractionation processes, we applied a permeation model for two different processes of bubble pressure build-up in the firn, "pressure sensitive process" (e.g., microbubbles: 0.3–3 % of air contents) with a greater sensitivity to overloading pressures and "normal bubble process". The model indicates that δAr/N2 in the bubbles under the pressure sensitive process are negatively correlated with the accumulation rate due to changes in overloading pressure. On the other hand, the normal bubbles experience only limited depletion (< 0.5 ‰) in the firn. Colder temperatures in the firn induce more depletion in δAr/N2 through thicker firn. The pressure sensitive bubbles are so depleted in δAr/N2 at the bubble close-off depth that they dominate the total δAr/N2 changes in spite of their smaller air contents. The model also indicates that δAr/N2 of ice cores should have experienced several per mil of depletion during the storage 14–18 years after coring. Further understanding of the δAr/N2 fractionation processes in the firn, combined with nitrogen and argon isotope data, may lead to a new proxy for the past temperature and accumulation rate.

scholarly journals On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

2012 ◽  
Vol 8 (4) ◽  
pp. 1239-1255 ◽  
Author(s):  
F. Parrenin ◽  
S. Barker ◽  
T. Blunier ◽  
J. Chappellaz ◽  
J. Jouzel ◽  
...  
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Convective Zone ◽  
East Antarctica ◽  
Column Height ◽  
Ice Flow ◽  
Depth Difference ◽  
Lock In ◽  
Last Deglacial

Abstract. 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. (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 general agreement of method 4 with methods 2 and 3 confirms that the bipolar seesaw antiphase happened during the last 140 kyr. Applying method 4 to the deeper section of the EDC core confirms that the ice flow is complex and can help to improve 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 suggest that it is due to an overestimation of the glacial lock-in depth (LID) by the firn densification model. In contrast, we find that method 1 very likely underestimates Δdepth during Termination II, due either to an underestimated thinning function or to an underestimated LID. Finally, method 2 gives estimates within a few metres of methods 3 and 4 during the last deglacial warming, suggesting that the convective zone at Dome C cannot have been very large at this time, if it existed at all.

The Paleochrono probabilistic model to derive a consistent chronology for several paleoclimatic sites

2021 ◽  
Author(s):  
Frédéric Parrenin ◽  
Lucie Bazin ◽  
Christo Buizert ◽  
Emilie Capron ◽  
Jai Chowdry Beeman ◽  
...  
Keyword(s):  
Probabilistic Model ◽  
Environmental Changes ◽  
Accumulation Rate ◽  
Ice Core ◽  
Sediment Cores ◽  
Computing Time ◽  
Ice Cores ◽  
Ease Of Use ◽  
Sequence Of Events ◽  
Different Types

&lt;p&gt;Past climatic and environmental changes can be reconstructed thanks to paleoclimatic archives such as ice cores, marine sediment cores, lake sediment cores, speleothems, tree rings, corals, etc. The dating of these natural archives is crucial for deciphering the temporal sequence of events during past climate changes. It is also essential to estimate the absolute and relative errors of such estimated chronologies. This task is, however, complex since it involves the combination of different dating approaches on different paleoclimatic sites and often different types of archives. Here we present Paleochrono, a new probabilistic model to derive a common and probalistically optimal chronology for several paleoclimatic sites with potentially different types of archives. Paleochrono is based on the inversion of an archiving model: a varying deposition rate (also named sedimentation or accumulation rate) and also,&amp;#160;for ice cores, a&amp;#160;lock-in-depth of air bubbles (since air is not trapped at surface) and a thinning function (since ice undergoes flow).&amp;#160;The model integrates several types of chronological information: prior knowledge of the archiving process, independently dated horizons, depth intervals of known duration, undated stratigraphic links between records, and, for ice cores, &amp;#916;depth observations (depth differences between synchronous events recorded in the bubbles and ice, respectively). The optimization is formulated as a least-squares problem, assuming that all densities of probabilities are near-Gaussian and that the model is almost linear in the vicinity of the best solution. Paleochrono is the successor of IceChrono, which was dealing only with ice-core records. Paleochrono&amp;#160;performs better than IceChrono in terms of computational efficiency, ease of use, and accuracy. We demonstrate the ability of Paleochrono in a new AICC2012-Hulu dating experiment, which combines the AICC2012 dating experiment, based on records from five polar ice cores,&amp;#160;with data from two U/Th-dated speleothems from Hulu Cave (China). We analyse the performance of Paleochrono in terms of computing time and memory usage in various dating experiments. Paleochrono is freely available under the MIT open source license.&lt;/p&gt;

Palaeoclimatic information from ice cores: the Vostok records

1990 ◽  
Vol 81 (4) ◽  
pp. 349-355 ◽  
Author(s):  
J. Jouzel ◽  
J. R. Petit ◽  
D. Raynaud
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Deuterium Content ◽  
High Concentration ◽  
Meridional Transport ◽  
Orbital Parameters ◽  
Continental Shelves ◽  
Precipitation Record ◽  
Present Rate

ABSTRACTIce deposits from Greenland and Antarctic ice sheets have stored over long periods of time information about the climate and environment of our planet. Attention will be focused on the 2083 m Vostok Antarctic ice core which represents a unusually long record (160 000 ka) due to the low accumulation rate (∼2 g cm−2a−1) and the rather uniform conditions of ice flow. This ice core provides a unique opportunity to obtain several palaeo-data such as temperature, accumulation (precipitation), aerosol loading, CO2 and trace gases over a full glacial-interglacial climatic cycle.The Vostok temperature, deduced from the interpretation of the deuterium content, and the CO2 records show a large 100 ka signal with a change of the order of 10°C and 70 ppmv respectively. The two records are closely correlated and both display shorter periodicities characteristic of the earth orbital parameters. CH4 concentrations also show variations from about 0·35 to about 0·65 ppmv linked with the glacial-interglacial warming. These features suggest a fundamental link between the climatic system and the carbon cycle and stress the role of radiatively active gases in climatic changes.The accumulation (precipitation) record appears to be governed by temperature with values during the coldest stages reduced by a factor of 2 with respect to the present rate. Ice deposited during these coldest stage is also characterised by high concentration of marine and terrestrial aerosols; these peaks probably reflect strengthened sources and meridional transport during full glacial conditions, linked to higher wind speed, more extensive arid areas on surrounding continent and a greater exposure of continental shelves.

scholarly journals Optimisation of glaciological parameters for ice core chronology by implementing counted layers between identified depth levels

2014 ◽  
Vol 10 (4) ◽  
pp. 3585-3616 ◽  
Author(s):  
L. Bazin ◽  
B. Lemieux-Dudon ◽  
A. Landais ◽  
M. Guillevic ◽  
P. Kindler ◽  
...  
Keyword(s):  
Bayesian Approach ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Age Difference ◽  
Sensitivity Tests ◽  
New Type ◽  
Lock In ◽  
Ice Core Dating

Abstract. A~recent coherent chronology has been built for 4 Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice cores chronology, it has been imposed that the AICC2012 chronology for NGRIP should respect exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited to constraints deduced from layer counting: the markers of age-difference. Using this type of markers for NGRIP in a 5 cores dating exercise with Datice, we have performed several sensitivity tests and show that the new ice core chronologies obtained with these new markers do not differ by more than 400 years from AICC2012 for Antarctic ice cores and by more than 130 years from GICC05 for NGRIP over the last 60 000 years. With this new parameterization, the accumulation rate and lock-in depth associated with NGRIP are more coherent with independent estimates than those obtained in AICC2012. While these new chronologies should not be used yet as new ice core chronologies, the improved methodology presented here should be considered in the next coherent ice core dating exercise.

scholarly journals La datation des archives glaciaires

2020 ◽  
pp. 018
Author(s):  
Frédéric Parrenin ◽  
Amaëlle Landais
Keyword(s):  
Probabilistic Model ◽  
Air Bubbles ◽  
Orbital Parameters ◽  
Sedimentation Process ◽  
Quaternary Climate ◽  
The Earth ◽  
Dating Methods ◽  
Glacial Sedimentation

Les glaces en Antarctique et au Groenland sont une archive de premier plan pour reconstruire le climat du Quaternaire. Une datation précise est nécessaire pour exploiter cette archive. Les méthodes de datation peuvent être tirées de l'analyse de la glace, des bulles d'air piégées, de la comparaison à d'autres archives ou aux variations des paramètres orbitaux de la Terre, ou de la modélisation du processus de sédimentation glaciaire. Ces méthodes étant complémentaires, un modèle probabiliste a été développé pour les combiner de manière optimale. Ice samplings from Antarctica or Greenland form an exceptional archive to reconstruct the Quaternary climate. An accurate chronology is necessary to exploit this archive. Dating methods can be derived from the analysis of ice, or enclosed air bubbles, from the comparison to other archives or to variations of orbital parameters of the Earth, or from the modelling of the glacial sedimentation process. These methods being complementary, a probabilistic model has been developed to combine them in an optimal manner.

scholarly journals Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2012 ◽  
Vol 8 (6) ◽  
pp. 6051-6091 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Clear Correlation ◽  
Last Deglaciation ◽  
Main Driver ◽  
Dronning Maud Land ◽  
James Ross Island ◽  
The Last Deglaciation ◽  
Lock In

Abstract. 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 δ15N 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 δ15N 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.

scholarly journals Post bubble-closeoff fractionation of gases in polar firn and ice cores: effects of accumulation rate on permeation through overloading pressure

2015 ◽  
Vol 15 (11) ◽  
pp. 15711-15753
Author(s):  
T. Kobashi ◽  
T. Ikeda-Fukazawa ◽  
M. Suwa ◽  
J. Schwander ◽  
T. Kameda ◽  
...  
Keyword(s):  
Negative Correlation ◽  
Environmental Changes ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Significant Negative Correlation ◽  
Ice Crystals ◽  
Orbital Parameters ◽  
Air Content ◽  
The Past

Abstract. Gases in ice cores are invaluable archives of past environmental changes (e.g., the past atmosphere). However, gas fractionation processes after bubble closure in the firn are poorly understood, although increasing evidence indicates preferential leakages of smaller molecules (e.g., neon, oxygen, and argon) from the closed bubbles through ice crystals. These fractionation processes are believed to be responsible for the observed millennial δO2/N2 variations in ice cores, linking ice core chronologies with orbital parameters. Herein, we found that δAr/N2 at decadal resolution on the gas age scale in the GISP2 ice core has a significant negative correlation with accumulation rate over the past 6000 years. Furthermore, the precise temperature and accumulation rate records over the past 4000 years are found to have nearly equal effects on δAr/N2 with sensitivities of 0.72 ± 0.1 ‰ °C−1 and −0.58 ± 0.09 ‰ (0.01 m ice yr−1)−1, respectively. To understand the fractionation processes, we applied a permeation model to "microbubbles (< 1 % of air content in the Vostok ice core)" and "normal bubbles" in the firn. The model indicates that δAr/N2 in the microbubbles is negatively correlated with the accumulation rate as found in the observation, due to changes in overloading pressure. Colder (warmer) temperatures in the firn induce more (less) depletions in δAr/N2. The microbubbles are so depleted in δAr/N2 at the bubble closeoff depth that they dominate the total δAr/N2 changes in spite of their smaller volumes. The model also indicates that δAr/N2 of GISP2 and NGRIP should have experienced several permil of depletion during the storage 14 years after coring. Further understanding of the δAr/N2 and δO2/N2 fractionation processes in the firn may lead to a new proxy for the past temperature and accumulation rate.

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