scholarly journals "EDML1": a chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years

2007 ◽  
Vol 3 (2) ◽  
pp. 549-574 ◽  
Author(s):  
U. Ruth ◽  
J.-M. Barnola ◽  
J. Beer ◽  
M. Bigler ◽  
T. Blunier ◽  
...  
Keyword(s):  
Heat Flux ◽  
Time Scales ◽  
Internal Consistency ◽  
Time Scale ◽  
Ice Core ◽  
Spatial Variations ◽  
Geothermal Heat ◽  
Ice Flow ◽  
Volcanic Events ◽  
Dronning Maud Land

Abstract. A chronology called EDML1 has been developed for the EPICA ice core from Dronning Maud Land (EDML). EDML1 is closely interlinked with EDC3, the new chronology for the EPICA ice core from Dome-C (EDC) through a stratigraphic match between EDML and EDC that consists of 322 volcanic match points over the last 128 ka. The EDC3 chronology comprises a glaciological model at EDC, which is constrained and later selectively tuned using primary dating information from EDC as well as from EDML, the latter being transferred using the tight stratigraphic link between the two cores. Finally, EDML1 was built by exporting EDC3 to EDML. For ages younger than 41 ka BP EDML1/EDC3 is based on dated volcanic events and on a match to the Greenlandic GICC05 time scale via 10Be and methane. The internal consistency between EDML1 and EDC3 is estimated to be typically ~6 years and always less than 450 years over the last 128 ka (always less than 130 years over the last 60 ka), which reflects an unprecedented synchrony of time scales. EDML1 ends at 150 ka BP (2417 m depth) because the match between EDML and EDC becomes ambiguous further down. This hints to a complex ice flow history for the deepest 350 m of the EDML ice core, which amongst other reasons may be caused by spatial variations of the geothermal heat flux.

scholarly journals "EDML1": a chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years

2007 ◽  
Vol 3 (3) ◽  
pp. 475-484 ◽  
Author(s):  
U. Ruth ◽  
J.-M. Barnola ◽  
J. Beer ◽  
M. Bigler ◽  
T. Blunier ◽  
...  
Keyword(s):  
Time Scales ◽  
Internal Consistency ◽  
Time Scale ◽  
Ice Core ◽  
Ice Flow ◽  
Volcanic Events ◽  
Dronning Maud Land

Abstract. A chronology called EDML1 has been developed for the EPICA ice core from Dronning Maud Land (EDML). EDML1 is closely interlinked with EDC3, the new chronology for the EPICA ice core from Dome-C (EDC) through a stratigraphic match between EDML and EDC that consists of 322 volcanic match points over the last 128 ka. The EDC3 chronology comprises a glaciological model at EDC, which is constrained and later selectively tuned using primary dating information from EDC as well as from EDML, the latter being transferred using the tight stratigraphic link between the two cores. Finally, EDML1 was built by exporting EDC3 to EDML. For ages younger than 41 ka BP the new synchronized time scale EDML1/EDC3 is based on dated volcanic events and on a match to the Greenlandic ice core chronology GICC05 via 10Be and methane. The internal consistency between EDML1 and EDC3 is estimated to be typically ~6 years and always less than 450 years over the last 128 ka (always less than 130 years over the last 60 ka), which reflects an unprecedented synchrony of time scales. EDML1 ends at 150 ka BP (2417 m depth) because the match between EDML and EDC becomes ambiguous further down. This hints at a complex ice flow history for the deepest 350 m of the EDML ice core.

scholarly journals Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

2013 ◽  
Vol 9 (6) ◽  
pp. 2489-2505 ◽  
Author(s):  
H. Fischer ◽  
J. Severinghaus ◽  
E. Brook ◽  
E. Wolff ◽  
M. Albert ◽  
...  
Keyword(s):  
Heat Flux ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Geothermal Heat ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Quaternary Climate ◽  
Drill Site ◽  
Heat Flow Model

Abstract. The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

scholarly journals Synchronisation of the EDML and EDC ice cores for the last 52 kyr by volcanic signature matching

2007 ◽  
Vol 3 (2) ◽  
pp. 409-433 ◽  
Author(s):  
M. Severi ◽  
S. Becagli ◽  
E. Castellano ◽  
A. Morganti ◽  
R. Traversi ◽  
...  
Keyword(s):  
Time Scale ◽  
Ice Core ◽  
Ice Cores ◽  
Time Duration ◽  
Ice Flow ◽  
Common Time ◽  
Temporal Intervals ◽  
Apparent Duration ◽  
Dronning Maud Land ◽  
The One

Abstract. A common time scale for the EPICA ice cores from Dome C (EDC) and Dronning Maud Land (EDML) was established. Since EDML core was not drilled on a dome, the development of the EDML1 time scale for the EPICA ice core drilled in Dronning Maud Land was carried on by creating a detailed stratigraphic link between this core and the one drilled at Dome C, dated by a simpler 1D ice-flow model. The synchronisation between the two ice cores was built via the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulfate, which was employed for the last 52 kyr of the record. By evaluating the ratio R of the apparent duration of temporal intervals between couples of isochrones, the depth comparison between the two cores was turned into an estimate of anomalies between the modelled EDC and EDML glaciological age models during the studied period. On average R ranges between 0.8 and 1.2 corresponding to an uncertainty within 20% in the estimate of the time duration in at least one of the two ice cores. Significant deviations of R up to 1.4–1.5 are observed between 18 and 28 kyr BP. At this step our approach is not able to unequivocally find out which of the models is affected by the errors, but assuming the thinning function at both sites and accumulation history at Dome C, which was drilled on a dome, as being correct, this anomaly can be ascribed to a complex spatial accumulation variability (which may be different at present day and in the past) and to upstream ice flow in the area of the EDML core.

scholarly journals Estimating the basal melt rate at NorthGRIP using a Monte Carlo technique

2007 ◽  
Vol 45 ◽  
pp. 137-142 ◽  
Author(s):  
Susanne L. Buchardt ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Heat Flux ◽  
Monte Carlo ◽  
Ice Core ◽  
Two Dimensional ◽  
Internal Layers ◽  
Large Area ◽  
Geothermal Heat ◽  
Ice Flow ◽  
Flow Models ◽  
Two Dimensional Flow

AbstractFrom radio-echo sounding (RES) surveys and ice core data it can be seen that the ice sheet is melting at the base in a large area in Northern Greenland. The RES images reveal internal layers in the ice. The layers are former deposition surfaces and are thus isochrones. Undulations of the isochrones in regions where the base is smooth suggest that the basal melt rate changes over short distances. This indicates that the geothermal heat flux is very high and has large spatial variability in Northern Greenland. In this study, the basal melt rate at the NorthGRIP drill site in North-Central Greenland is calculated by inverse modelling. We use simple one- and two-dimensional flow models to simulate the ice flow along the NNW-trending ice ridge leading to NorthGRIP. The accumulation is calculated from a dynamical model. Several ice flow parameters are unknown and must be estimated along with the basal melt rate using a Monte Carlo method. The Monte Carlo inversion is constrained by the observed isochrones, dated from the timescale established for the NorthGRIP ice core. The estimates of the basal melt rates around NorthGRIP are obtained from both the one- and two-dimensional models. Combining the estimated basal melt rates with the observed borehole temperatures allows us to convert the basal melt rates to geothermal heat flow values. From the two-dimensional model we find the basal melt rate and geothermal heat flux at NorthGRIP to be 6.1 mma–1 and 129 mWm–2, respectively.

Time Scale and Ice Accumulation During the Last 125,000 Years as Indicated by the Greenland 018 curve

1972 ◽  
Vol 109 (1) ◽  
pp. 17-24 ◽  
Author(s):  
N. A. Mörner
Keyword(s):  
North America ◽  
Time Scales ◽  
Time Scale ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climatic Changes ◽  
Dynamic Changes ◽  
Ice Accumulation

SummaryThe 18 curve from the 1390 m long ice core from Camp Century, Greenland, shows climatic changes that are easily correlated with known glacial and non-glacial events of North America and north Europe and are thus indirectly dated. With a known chronology, the glacial dynamic changes of the Greenland Ice Sheet can be calculated for the last 125,000 years. It is concluded that the dynamics of the Greenland Ice Sheet have changed drastically during this period and that these changes are directly related to major changes of climate and extension of the Wisconsin and Weichselian glaciations. Logarithmic time scales earlier applied to this curve must therefore be incorrect.

scholarly journals Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica

2013 ◽  
Vol 59 (213) ◽  
pp. 9-20 ◽  
Author(s):  
Reinhard Drews ◽  
Carlos Martín ◽  
Daniel Steinhage ◽  
Olaf Eisen
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Radar Data ◽  
Ice Thickness ◽  
Atmospheric Conditions ◽  
Ice Flow ◽  
International Partnerships ◽  
Drill Site ◽  
Dronning Maud Land

AbstractWe present a comprehensive approach (including field data, remote sensing and an anisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land, Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m−2 a−1 due to preferred wind directions and changing surface slope. The stratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.

scholarly journals The EDC3 chronology for the EPICA Dome C ice core

2007 ◽  
Vol 3 (3) ◽  
pp. 485-497 ◽  
Author(s):  
F. Parrenin ◽  
J.-M. Barnola ◽  
J. Beer ◽  
T. Blunier ◽  
E. Castellano ◽  
...  
Keyword(s):  
Pattern Matching ◽  
Time Scales ◽  
Excellent Agreement ◽  
Time Scale ◽  
Flow Model ◽  
Ice Core ◽  
Snow Accumulation ◽  
The Core ◽  
Time Periods ◽  
Paleoclimatic Records

Abstract. 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 mechanical 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. Discrepancies 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 uncertainty of 6 kyr back to 800 kyr.

scholarly journals Where is the 1-million-year-old ice at Dome A?

2018 ◽  
Vol 12 (5) ◽  
pp. 1651-1663 ◽  
Author(s):  
Liyun Zhao ◽  
John C. Moore ◽  
Bo Sun ◽  
Xueyuan Tang ◽  
Xiaoran Guo
Keyword(s):  
Heat Flux ◽  
Depth Profile ◽  
Ice Core ◽  
Three Dimensional ◽  
Melting Rate ◽  
Dome A ◽  
Geothermal Heat ◽  
Kunlun Station ◽  
Ice Fabrics ◽  
Basal Melting

Abstract. Ice fabric influences the rheology of ice, and hence the age–depth profile at ice core drilling sites. To investigate the age–depth profile to be expected of the ongoing deep ice coring at Kunlun station, Dome A, we use the depth-varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows for the simulation of the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which consequently control the age profile. Constraining modeled age–depth profiles with dated radar isochrones to 2∕3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 ka BP, limits the age of the deep ice at Kunlun to between 649 and 831 ka, a much smaller range than previously inferred. The simple interpretation of the polarimetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mW m−2. A heat flux of 50 mW m−2 is too low to fit the deeper radar layers, and 60 mW m−2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2–2.7 mm a−1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1-million-year-old ice may be found 200 m above the bed, and that there are large regions where even older ice is well above the bedrock within 5–6 km of the Kunlun station.

scholarly journals How old is the ice beneath Dome A, Antarctica?

2014 ◽  
Vol 8 (1) ◽  
pp. 289-305 ◽  
Author(s):  
B. Sun ◽  
J. C. Moore ◽  
T. Zwinger ◽  
Z. Liyun ◽  
D. Steinhage ◽  
...  
Keyword(s):  
Heat Flux ◽  
Thermal State ◽  
Ice Core ◽  
Three Dimensional ◽  
Glacial Cycle ◽  
Dome A ◽  
Geothermal Heat ◽  
Surface Conditions ◽  
Kunlun Station ◽  
Ice Fabrics

Abstract. Chinese scientists will start to drill a deep ice core at Kunlun station near Dome A in the near future. Recent work has predicted that Dome A is a location where ice older than 1 million years can be found. We model flow, temperature and the age of the ice by applying a three-dimensional, thermo-mechanically coupled full-Stokes model to a 70 km × 70 km domain around Kunlun station, using isotropic non-linear rheology and different prescribed anisotropic ice fabrics that vary the evolution from isotropic to single maximum at 1/3 or 2/3 depths. The variation in fabric is about as important as the uncertainties in geothermal heat flux in determining the vertical advection which in consequence controls both the basal temperature and the age profile. We find strongly variable basal ages across the domain since the ice varies greatly in thickness and any basal melting effectively removes very old ice in the deepest parts of the subglacial valleys. Comparison with dated radar isochrones in the upper one third of the ice sheet cannot sufficiently constrain the age of the deeper ice, with uncertainties as large as 500 000 yr in the basal age. We also assess basal age and thermal state sensitivities to geothermal heat flux and surface conditions. Despite expectations of modest changes in surface height over a glacial cycle at Dome A, even small variations in the evolution of surface conditions cause large variation in basal conditions which is consistent with basal accretion features seen in radar surveys.

scholarly journals Inversion of geothermal heat flux in a thermomechanically coupled nonlinear Stokes ice sheet model

2016 ◽  
Author(s):  
Hongyu Zhu ◽  
Noemi Petra ◽  
Georg Stadler ◽  
Tobin Isaac ◽  
Thomas J. R. Hughes ◽  
...  
Keyword(s):  
Heat Flux ◽  
Inverse Problem ◽  
Optimization Problem ◽  
Premature Termination ◽  
Adjoint Equations ◽  
Surface Velocity ◽  
Geothermal Heat ◽  
Ice Flow ◽  
Cost Functional ◽  
The Cost

Abstract. We address the inverse problem of inferring the basal geothermal heat flux from surface velocity observations using an instantaneous thermomechanically coupled nonlinear Stokes ice flow model. This is a challenging inverse problem since the map from basal heat flux to surface velocity observables is indirect: the heat flux is a boundary condition for the thermal advection-diffusion equation, which couples to the nonlinear Stokes ice flow equations, which then determine the surface ice flow velocity. This multiphysics inverse problem is formulated as a nonlinear least-squares optimization problem with a cost functional that includes the data misfit between surface velocity observations and model predictions. A Tikhonov regularization term is added to render the problem well-posed. We derive adjoint-based gradient and Hessian expressions for the resulting PDE-constrained optimization problem and propose an inexact Newton method for its solution. As a consequence of the Petrov-Galerkin discretization of the energy equation, we show that discretization and differentiation do not commute; that is, the order in which we discretize the cost functional and differentiate it affects the correctness of the gradient. Using two and three-dimensional model problems, we study the prospects for and limitations of the inference of the geothermal heat flux field from surface velocity observations. The results show that the reconstruction improves as the noise level in the observations decreases, and that small wavelength variations in the geothermal heat flux are difficult to recover. We analyze the ill-posedness of the inverse problem as a function of the number of observations by examining the spectrum of the Hessian of the cost functional. Motivated by the popularity of operator-split or staggered solvers for forward multiphysics problems — i.e., those that drop two-way coupling terms to yield a one-way coupled forward Jacobian — we study the effect on the inversion of a one-way coupling of the adjoint energy and Stokes equations. We show that taking such a one-way coupled approach for the adjoint equations can lead to an incorrect gradient and premature termination of optimization iterations due to loss of a descent direction stemming from inconsistency of the gradient with the contours of the cost functional. Nevertheless, one may still obtain a reasonable approximate inverse solution particularly if important features of the reconstructed solution emerge early in optimization iterations, before the premature termination.

Sign in / Sign up

Export Citation Format

Share Document