scholarly journals Reconstructing ice-sheet accumulation rates at ridge B, East Antarctica

2004 ◽  
Vol 39 ◽  
pp. 326-330 ◽  
Author(s):  
Gwendolyn J.-M. C. Leysinger Vieli ◽  
Martin J. Siegert ◽  
Antony J. Payne
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Ice Flow ◽  
One Dimensional ◽  
Ice Accumulation ◽  
Core Site ◽  
Past Climate Change

AbstractUnderstanding how ice sheets responded to past climate change is fundamental to forecasting how they will respond in the future. Numerical models calculating the evolution of ice sheets depend upon accumulation data, which are principally available from ice cores. Here, we calculate past rates of ice accumulation using internal layering. The englacial structure of the East Antarctic ice divide at ridge B is extracted from airborne ice-penetrating radar. The isochronous surfaces are dated at their intersection with the Vostok ice-core site, where the depth–age relationship is known. The dated isochrons are used as input to a one-dimensional ice-flow model to investigate the spatial accumulation distribution. The calculations show that ice-accumulation rates generally increase from Vostok lake towards ridge B. The western flank of the ice divide experiences markedly more accumulation than in the east. Further, ice accumulation increases northwards along the ice divide. The results also show the variability of accumulation in time and space around the ridge B ice divide over the last 124 000 years.

scholarly journals Change of the ice rheology with climatic transitions – implication on ice flow modelling and dating of the EPICA Dome C core

2006 ◽  
Vol 2 (6) ◽  
pp. 1187-1219 ◽  
Author(s):  
G. Durand ◽  
F. Gillet-Chaulet ◽  
A. Svensson ◽  
O. Gagliardini ◽  
S. Kipfstuhl ◽  
...  
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Horizontal Shear ◽  
Ice Flow ◽  
Flow Modelling ◽  
The Past ◽  
Ice Flows ◽  
Crystallographic Orientations

Abstract. The study of the distribution of the crystallographic orientations (the fabric) along ice cores supplies information on the past and current ice flows of ice-sheets. Beside the usually observed formation of a vertical single maximum fabric, the EPICA Dome Concordia ice core (EDC) shows an abrupt and unexpected strenghtening of its fabric during termination II around 1750 m depth. Such strengthenings were already observed for sites located on an ice-sheet. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in viscosity and investigate its implication on ice flow and dating.

Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations from South Pole and EPICA Dome C ice cores

2020 ◽  
Author(s):  
Carlos Martin ◽  
Howard Conway ◽  
Michelle Koutnik ◽  
Catherine Ritz ◽  
Thomas Bauska ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Crystal Orientation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
South Pole ◽  
Ice Flow ◽  
Phase Sensitive ◽  
Glacial Periods ◽  
Ice Core Records

<p>The climatic conditions over ice sheets at the time of snow deposition and compaction imprint distinctive crystallographic properties to the resulting ice. As the snow gets buried, its macroscopic structure evolves due to vertical compression but retains traces of the climatic imprint that generate distinctive mechanical, thermal and optical properties. Because climate alternates between glaciar periods, that are colder and dustier, and interglacial periods, the ice sheets are composed from layers with alternating mechanical properties. Here we compare ice core dust content and crystal orientation fabrics, from the ice core records, with englacial vertical strain-rates, measured with a phase-sensitive radar (ApRES), at South Pole and EPICA Dome C ice cores. Similarly to previous observations, we show that ice deposited during glacial periods develops stronger crystal orientation fabrics. In addition, we show that ice deposited during glacial periods is harder to vertically compress and horizontally extend, up to about 3 times, but softer to shear. These variations in mechanical properties are typically ignored in ice-flow modelling but they could be critical to interpret ice core records. Also, we show that the changes in crystal orientation fabrics due to transitions from interglacial to glacial conditions can be detected by phase-sensitive radar. This information can be used to constrain age-depth in future ice-core locations.</p>

scholarly journals How well can we parameterize past accumulation rates in polar ice sheets?

1997 ◽  
Vol 25 ◽  
pp. 418-422 ◽  
Author(s):  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
Order Approximation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
First Order Approximation

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

scholarly journals Change in ice rheology during climate variations – implications for ice flow modelling and dating of the EPICA Dome C core

2007 ◽  
Vol 3 (1) ◽  
pp. 155-167 ◽  
Author(s):  
G. Durand ◽  
F. Gillet-Chaulet ◽  
A. Svensson ◽  
O. Gagliardini ◽  
S. Kipfstuhl ◽  
...  
Keyword(s):  
Effective Viscosity ◽  
Flow Model ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Climate Variations ◽  
Horizontal Shear ◽  
Ice Flow ◽  
Flow Modelling ◽  
Crystallographic Orientations

Abstract. 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.

scholarly journals Advection Impacts the Firn Structure of Greenland's Percolation Zone

2019 ◽  
Author(s):  
Rosemary Leone ◽  
Joel Harper ◽  
Toby Meierbachtol ◽  
Neil Humphrey
Keyword(s):  
Ice Core ◽  
Heat Content ◽  
Ice Flow ◽  
Surface Conditions ◽  
One Dimensional ◽  
Climate Gradients ◽  
Column Structure ◽  
Core Site ◽  
The Impact ◽  
Percolation Zone

Abstract. One dimensional simulations of firn evolution neglect horizontal transport during burial. Using a suite of model runs, we demonstrate the impacts of advection on the development of firn density, temperature, and the stratigraphy of melt features the 0Greenland ice sheet percolation zone. The simulations isolate processes in synthetic runs, and investigate four specific transects and an ice core site. The advection process tends to increase the pore close-off depth, reduce the heat content, and decrease the frequency of melt features with depth by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Horizontal ice flow interacts with topography, climate gradients, and meltwater infiltration to influence the evolution of the firn column structure; the interaction between these variables modulates the impact of advection on firn at locations around Greenland. Pore close-off and firn temperature are mainly impacted in the lowermost 20 km of the percolation zone, which may be relevant to migration of the lower percolation zone. Relatively high in the percolation zone, however, the stratigraphy of melt features can have an advection derived component that should not be conflated with changing climate.

scholarly journals How well can we parameterize past accumulation rates in polar ice sheets?

1997 ◽  
Vol 25 ◽  
pp. 418-422 ◽  
Author(s):  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
Order Approximation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
First Order Approximation

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

A novel high-resolution laser-melting sampler for discrete analyses of ion concentrations and stable water isotopic compositions in firn and ice cores

2021 ◽  
Author(s):  
Yuko Motizuki ◽  
Yoichi Nakai ◽  
Kazuya Takahashi ◽  
Junya Hirose ◽  
Yu Vin Sahoo ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Cores ◽  
Depth Resolution ◽  
Climatic Changes ◽  
Accumulation Rates ◽  
Laser Melting ◽  
Ion Concentrations ◽  
Annual Layer ◽  
Annual Resolution ◽  
High Depth

<p>Ice cores preserve past climatic changes and, in some cases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser melting. A hole in an ice core approximately 3 mm in diameter is melted and heated well below the boiling point by laser irradiation, and the meltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser fiber. The advantage of sampling by laser melting is that molecular ion concentrations and stable water isotope compositions in ice cores can be measured at high depth resolution, which is advantageous for ice cores with low accumulation rates. This device takes highly discrete samples from ice cores, attaining depth resolution as small as ~3 mm with negligible cross contamination; the resolution can also be set at longer lengths suitable for validating longer-term profiles of various ionic and water isotopic constituents in ice cores. This technique allows the detailed reconstruction of past climatic changes at annual resolution and the investigation of transient ionic and isotopic signals within single annual layers in low-accumulation cores, potentially by annual layer counting.</p>

Reconstructing Antarctic snow accumulation using nitrogen isotopes of nitrate

2021 ◽  
Author(s):  
Pete D. Akers ◽  
Joël Savarino ◽  
Nicolas Caillon ◽  
Mark Curran ◽  
Tas Van Ommen
Keyword(s):  
Nitrogen Isotopes ◽  
Full Range ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Accumulation Rates ◽  
Sea Levels ◽  
Antarctic Snow ◽  
Parallel Reconstruction

<p>Precise Antarctic snow accumulation estimates are needed to understand past and future changes in global sea levels, but standard reconstructions using water isotopes suffer from competing isotopic effects external to accumulation. We present here an alternative accumulation proxy based on the post-depositional photolytic fractionation of nitrogen isotopes (d<sup>15</sup>N) in nitrate. On the high plateau of East Antarctica, sunlight penetrating the uppermost snow layers converts snow-borne nitrate into nitrogen oxide gas that can be lost to the atmosphere. This nitrate loss favors <sup>14</sup>NO<sub>3</sub><sup>-</sup> over <sup>15</sup>NO<sub>3</sub><sup>-</sup>, and thus the d<sup>15</sup>N of nitrate remaining in the snow will steadily increase until the nitrate is eventually buried beneath the reach of light. Because the duration of time until burial is dependent upon the rate of net snow accumulation, sites with lower accumulation rates have a longer burial wait and thus higher d<sup>15</sup>N values. A linear relationship (r<sup>2</sup> = 0.86) between d<sup>15</sup>N and net accumulation<sup>-1</sup> is calculated from over 120 samples representing 105 sites spanning East Antarctica. These sites largely encompass the full range of snow accumulation rates observed in East Antarctica, from 25 kg m-<sup>2</sup> yr<sup>-1</sup> at deep interior sites to >400 kg m-<sup>2</sup> yr<sup>-1</sup> at near coastal sites. We apply this relationship as a transfer function to an Aurora Basin ice core to produce a 700-year record of accumulation changes. Our nitrate-based estimate compares very well with a parallel reconstruction for Aurora Basin that uses volcanic horizons and ice-penetrating radar. Continued improvements to our database may enable precise independent estimates of millennial-scale accumulation changes using deep ice cores such as EPICA Dome C and Beyond EPICA-Oldest Ice.</p>

scholarly journals Crystal growth of air hydrates over 720 ka in Dome Fuji (Antarctica) ice cores: microscopic observations of morphological changes below 2000 m depth

2011 ◽  
Vol 57 (206) ◽  
pp. 1017-1026 ◽  
Author(s):  
Tsutomu Uchida ◽  
Atsushi Miyamoto ◽  
Atsushi Shin’yama ◽  
Takeo Hondoh
Keyword(s):  
Crystal Growth ◽  
Morphological Changes ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Climatic Changes ◽  
Size Distributions ◽  
Number Density ◽  
Average Size

AbstractAir-hydrate crystals store most of the ancient air contained in deep ice sheets. We carried out microscopic observations of air-hydrate crystals below 2000 m depth within the ice core from Dome Fuji, Antarctica, to obtain their number and size distributions. We found that the number density continuously decreased with depth, whereas the average size increased, in contrast to findings from shallower depths. In addition, the characteristic perturbations in both number density and average size distribution with climatic changes almost disappeared, although they are clearly observed in shallow cores. These results indicate that the air-hydrate crystals grow considerably in deeper parts of the ice sheet, and this growth is accompanied by the diffusion of air molecules in the ice. The permeation coefficient of the air molecules in the ice sheet was estimated from the geometric parameters of the air-hydrate distributions. This is the first practical evidence comparable to the previous model estimations. It allows us to evaluate the impacts of the air-molecule migration in the ice sheet on the paleoclimatic information recorded in the deep ice cores.

8. Glaciers of the past

2018 ◽  
pp. 146-152
Author(s):  
David J. A. Evans
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Imagery ◽  
The Past ◽  
Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

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