scholarly journals Is there 1.5-million-year-old ice near Dome C, Antarctica?

2017 ◽  
Vol 11 (6) ◽  
pp. 2427-2437 ◽  
Author(s):  
Frédéric Parrenin ◽  
Marie G. P. Cavitte ◽  
Donald D. Blankenship ◽  
Jérôme Chappellaz ◽  
Hubertus Fischer ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheets ◽  
Atmospheric Composition ◽  
Regional Environment ◽  
Ice Flow ◽  
True Nature ◽  
Flow Modelling ◽  
North East ◽  
Geothermal Flux

Abstract. Ice sheets provide exceptional archives of past changes in polar climate, regional environment and global atmospheric composition. The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching ∼ 800 000 years. Obtaining an older paleoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we use internal isochrones, identified from airborne radar coupled to ice-flow modelling to estimate the age of basal ice along transects in the Dome C area. Three glaciological properties are inferred from isochrones: surface accumulation rate, geothermal flux and the exponent of the Lliboutry velocity profile. We find that old ice (> 1.5 Myr, 1.5 million years) likely exists in two regions: one ∼ 40 km south-west of Dome C along the ice divide to Vostok, close to a secondary dome that we name Little Dome C (LDC), and a second region named North Patch (NP) located 10–30 km north-east of Dome C, in a region where the geothermal flux is apparently relatively low. Our work demonstrates the value of combining radar observations with ice flow modelling to accurately represent the true nature of ice flow, and understand the formation of ice-sheet architecture, in the centre of large ice sheets.

scholarly journals Is there 1.5 million-year old ice near Dome C, Antarctica?

2017 ◽  
Author(s):  
Frédéric Parrenin ◽  
Marie G. P. Cavitte ◽  
Donald D. Blankenship ◽  
Jérome Chappellaz ◽  
Hubertus Fischer ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheets ◽  
Atmospheric Composition ◽  
Regional Environment ◽  
Ice Flow ◽  
True Nature ◽  
Flow Modelling ◽  
North East ◽  
Geothermal Flux

Abstract. Ice sheets provide exceptional archives of past changes in polar climate, regional environment and global atmospheric composition. The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching ~ 800,000 years. Obtaining an older paleoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we use internal isochrones, identified from airborne radar coupled to ice-flow modelling to estimate the age of basal ice along transects in the Dome C area. Three glaciological properties are inverted from isochrones: surface accumulation rate; geothermal flux; and the exponent of the Lliboutry velocity profile. We find that old ice (> 1 Myr, 1 million years) likely exists in two regions: one ~ 40 km south-west of Dome C along the ice divide to Vostok, close to a secondary dome that we name "Little Dome C" (LDC); and a second region named "North Patch" (NP) located 10–30 km north-east of Dome C, in a region where the geothermal flux is apparently relatively low. Our work demonstrates the value of combining radar observations with ice flow modelling to accurately represent the true nature of ice flow, and the formation of ice-sheet architecture, in the centre of large ice sheets.

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.

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 At what depth is the Eemian layer expected to be found at NEEM?

2008 ◽  
Vol 48 ◽  
pp. 100-102 ◽  
Author(s):  
Susanne L. Buchardt ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Monte Carlo Analysis ◽  
Interglacial Period ◽  
Ice Flow ◽  
North West ◽  
Flow Parameters ◽  
Drill Site ◽  
Radio Echo Sounding

AbstractNo continuous record from Greenland of the Eemian interglacial period (130–115 ka BP) currently exists. However, a new ice-core drill site has been suggested at 77.449˚ N, 51.056˚Win north-west Greenland (North Eemian or NEEM). Radio-echo sounding images and flow model investigations indicate that an undisturbed Eemian record may be obtained at NEEM. In this work, a two-dimensional ice flow model with time-dependent accumulation rate and ice thickness is used to estimate the location of the Eemian layer at the new drill site. The model is used to simulate the ice flow along the ice ridge leading to the drill site. Unknown flow parameters are found through a Monte Carlo analysis of the flow model constrained by observed isochrones in the ice. The results indicate that the Eemian layer is approximately 60m thick and that its base is located approximately 100m above bedrock.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1 at GRIP to 0.19 m ice equivalent year−1 50 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1at GRIP to 0.19 m ice equivalent year−150 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals Interpretation of the Temperature Profile Measured at Vostok, East Antarctica

1989 ◽  
Vol 12 ◽  
pp. 138-144 ◽  
Author(s):  
Catherine Ritz
Keyword(s):  
Surface Temperature ◽  
Temperature Profile ◽  
Accumulation Rate ◽  
Ice Core ◽  
Measured Temperature ◽  
Surface Temperature Change ◽  
Subglacial Lake ◽  
Polar Ice Sheets ◽  
Vostok Station ◽  
Geothermal Flux

The temperature profile measured in the Vostok bore hole is analysed. The temperature distribution in polar ice sheets depends mainly on past surface temperature, geothermal flux, and accumulation rate. In the present work, the heat equation is solved both for ice and for the underlying bedrock. The Vostok ice core offers a 160 000 year climatic record which is used to define the past surface temperature, while accumulation-rate variations are assumed to be governed by the saturation vapour pressure. The model is run for a number of different sets of parameters in order to find the parameter associations giving a good fit between the observed and the computed temperature profiles. With this model, it is possible to simulate the measured temperature profile within 0.1°C. To obtain this good fit, geothermal flux has to be higher than 50 mW/m2 and present-day accumulation rate must be lower than 2.6 cm/year. Sensitivity of these results both to the amplitude of surface-temperature change and to the velocity profile with depth is also investigated. Finally, it is shown that ice is at the melting point at the base of the ice sheet, which is in agreement with the presence of a subglacial lake near Vostok Station.

scholarly journals EXTRACTION OF ICE SHEET LAYERS FROM TWO INTERSECTED RADAR ECHOGRAMS NEAR NEEM ICE CORE IN GREENLAND

2016 ◽  
Vol XLI-B7 ◽  
pp. 585-591 ◽  
Author(s):  
S. Xiong ◽  
J.-P. Muller
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Electromagnetic Properties ◽  
Flow Mode ◽  
Internal Layers ◽  
Ice Flow ◽  
The North ◽  
Radar Echo ◽  
Echo Sounder

Accumulation of snow and ice over time result in ice sheet layers. These can be remotely sensed where there is a contrast in electromagnetic properties, which reflect variations of the ice density, acidity and fabric orientation. Internal ice layers are assumed to be isochronous, deep beneath the ice surface, and parallel to the direction of ice flow. The distribution of internal layers is related to ice sheet dynamics, such as the basal melt rate, basal elevation variation and changes in ice flow mode, which are important parameters to model the ice sheet. Radar echo sounder is an effective instrument used to study the sedimentology of the Earth and planets. Ice Penetrating Radar (IPR) is specific kind of radar echo sounder, which extends studies of ice sheets from surface to subsurface to deep internal ice sheets depending on the frequency utilised. In this study, we examine a study site where folded ice occurs in the internal ice sheet south of the North Greenland Eemian ice drilling (NEEM) station, where two intersected radar echograms acquired by the Multi-channel Coherent Radar Depth Sounder (MCoRDS) employed in the NASA’s Operation IceBridge (OIB) mission imaged this folded ice. We propose a slice processing flow based on a Radon Transform to trace and extract these two sets of curved ice sheet layers, which can then be viewed in 3-D, demonstrating the 3-D structure of the ice folds.

scholarly journals The Influence On Atmospheric Composition of Volcanic Eruptions as Derived From Ice-Core Analysis

1985 ◽  
Vol 7 ◽  
pp. 125-129 ◽  
Author(s):  
C.U. Hammer
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Atmospheric Composition ◽  
Core Analysis ◽  
Polar Ice ◽  
Ice Caps ◽  
The Past ◽  
Polar Ice Sheets

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.

scholarly journals Isochrones and isotherms beneath migrating ice divides

2002 ◽  
Vol 48 (160) ◽  
pp. 95-108 ◽  
Author(s):  
Nadine A. Nereson ◽  
Edwin D. Waddington
Keyword(s):  
Heat Flow ◽  
Migration Rate ◽  
Accumulation Rate ◽  
Ice Sheets ◽  
Temperature Measurements ◽  
Analytical Models ◽  
Ice Thickness ◽  
Ice Flow ◽  
Trailing Edges ◽  
History Of

AbstractWe use simple numerical and analytical models of ice flow and heat flow to characterize the shape of isochrones and isotherms beneath moving ice divides. Both nonlinear ice flow and reduced accumulation (wind scouring) at a divide can cause reduced downward flow in a region about one ice thickness wide under a divide. Greater downward velocities on the flanks cause isochrones and isotherms to become arched at depth. The magnitudes and shapes of these arches depend on the history of divide position. Arch amplitudes decrease by approximately e−1 for each increase in migration rate of 3–5 times the accumulation rate, the arches become asymmetric, with steeper leading edges and more gentle trailing edges, and the arch apex lags behind the divide. Isochrone and isotherm shapes can be used to infer past divide motions. In advection-dominated ice sheets, isochrone shapes record a longer history of divide position than do isotherm shapes. The opposite is true for diffusion-dominated ice sheets, in which a spatial array of ice-temperature measurements might extend the recorded history of divide position.

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