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New temperature profile measurements in the EPICA Dome C borehole EGU, 2008, Vienne Autriche |
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2008 |
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902 |
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5922 |
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Catherine Ritz, Eric Lefebvre, Dorthe Dahl Jensen, Sigfus Johnsen and Simon Sheldon |
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Title |
Temperature profile measurement in the EPICA Dome C borehole |
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Conference - International - Poster |
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2010 |
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The temperature field within ice sheets results from interactions between heat transfert, ice dynamics and boundary conditions such as geothermal heat flux and surface temperature. Therefore information concerning these factors can be inferred from the observed temperature profile in deep boreholes drilled in ice.
We present here a temperature profile measured in november 2008 in the EPICA Dome C borehole. The high-resolution of the measurements allows to estimate the temporal and spatial characteristics of temperature perturbation due to fluid convection.
The observed temperature profile indicates that the ice-bed interface is at the melting point . The vertical temperature gradient is not consistent with a 1D temperature field and this point must be clarified before using the temperature profile as a paleo thermometer.
Poster presented at the EPICA meeting – Roma, April 2010 |
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902 |
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626 |
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Author |
Legresy, B., S. Zhang, R. Hurd, P. Lacroix and R. Coleman. |
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Title |
Snow surface roughness at Dome C, Antarctica. |
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Conference - International - Poster |
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2010 |
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IPY conference, OSLO, june 2010. |
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902 |
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630 |
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Pol K, Masson-Delmotte V, Johnsen S, Bigler M, Cattani O, Durand G, Falourd S, Jouzel J, Minster B, Parrenin F, Ritz C, Steen-Larsen HC, Stenni B, |
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New MIS 19 EPICA Dome C high resolution deuterium data: Hints for a problematic preservation of climate variability at sub-millennial scale in the “oldest ice”
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Journal Article |
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2010 |
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Earth and Planetary Science Letters |
Abbreviated Journal |
Earth Planet. Sci. Lett. |
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298 |
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1-2 |
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95 -103 |
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water stable isotopes, ice cores, Antarctica, isotopic diffusion, |
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902 |
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0012-821X |
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yes |
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2009 |
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Author |
Gusmeroli Alessio, Pettit Erin C, Kennedy Joseph H, Ritz Catherine, |
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Title |
The crystal fabric of ice from full-waveform borehole sonic logging
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Journal Article |
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2012 |
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J. Geophys. Res. |
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117 |
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F3 |
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F03021- |
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Ice anisotropy, borehole sonic logging, ice crystal fabric, 0726 Cryosphere: Ice sheets, 0915 Exploration Geophysics: Downhole methods, 0935 Exploration Geophysics: Seismic methods (3025, 7294), |
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Abstract |
In an ice sheet, a preferred crystal orientation fabric affects deformation rates because ice crystals are strongly anisotropic: shear along the basal plane is significantly easier than shear perpendicular to the basal plane. The effect of fabric can be as important as temperature in defining deformation rates. Fabric is typically measured using analysis of thin sections under the microscope with co-polarized light. Due to the time-consuming and destructive nature of these measurements, however, it is difficult to capture the spatial variation in fabric necessary for evincing ice sheet flow patterns. Because an ice crystal is similarly elastically anisotropic, the speed of elastic waves through ice can be used as a proxy for quantify anisotropy. We use borehole sonic logging measurements and thin section data from Dome C, East Antarctica to define the relations between apparent fabric and borehole measured elastic speeds (compressional VP and vertically polarized shear VSV). These relations, valid for single maximum fabrics, allow in-situ, depth-continuous fabric estimates of unimodal fabric strength from borehole sonic logging. We describe the single maximum fabric using a1: the largest eigenvalue of the second-order orientation tensor. For ice at -16C and a1 in the 0.7-1 range the relations are VP = 248 a13.7 + 3755 m s-1 and VSV = -210a17.3 + 1968 m s-1.
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902 |
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AGU |
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0148-0227 |
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yes |
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505 |
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Author |
Erin Pettit, Edwin Waddington, Throstur Thorsteinsson, Alessio Gusmeroli, Joseph Kennedy,Catherine Ritz, and Regina Carns. |
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Title |
Using Borehole Sonic Logging to Infer Ice Microstructure and Climate History |
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Conference - International - Communication |
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Year |
2011 |
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Vol. 13, EGU2011-14160, 2011 |
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The physical properties of ice from glacial time periods appear to differ from those from interglacial time periods. Glacial ice typically has smaller crystals, higher impurity content, and stronger fabric (preferred orientation of crystal c-axes). Because ice deformation is sensitive to the orientation of crystals, the fabric affects patterns of ice flow, which in turn affects estimates of annual-layer thinning rates and the depth-age scale for ice-core records.Furthermore, a positive feedback exists between development of crystal fabric and ice deformation such that under
certain stress conditions, a climate-induced variation of fabric near the surface may be enhanced through time and depth in an ice sheet.
We use borehole sonic logging to measure both compressional-wave (p-wave) speed which we use to infer a continuous profile of the fabric (after corrections for temperature and porosity). The speed for p-waves propagating along the c-axes is higher than the speed for waves propagating across the c-axes. Near ice-sheet centers, where the ice typically develops a vertical single maximum fabric, the p-wave speed in the vertical direction (along the axis of the borehole) provides a measure of the strength of the fabric for a volume of ice 3m along the length of the borehole and approximately 1m radius deep into the ice.
We review and compare borehole sonic-logging data from boreholes in the Greenland and Antarctic ice
sheets. The Antarctic profiles show a stronger gradient in fabric during major climate transitions than the Greenland borehole profiles. Both ice sheets, however, eventually reach similar fabric strength at depth. We find that the strength of fabric derived from p-wave speed matches thin-section data for single maxima fabrics and is highly correlated with oxygen isotope ratios, suggesting a direct link to climate history. The p-wave speed is high (strong fabric) during periods of extremely negative oxygen isotope ratios (glacial periods). Furthermore, the
magnitude of the variability of the p-wave speed and its correlation with oxygen isotopes increases with depth;this provides evidence in support of the positive feedback mechanism between fabric development, deformation,and climate. |
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902 |
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3587 |
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Alessio Gusmeroli, Erin Pettit, Catherine Ritz, Joseph Kennedy, Maurine Montagnat, Eric
Lefebvre, Gael Durand, Sepp Kipfstuhl, and Simon Sheldon. |
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The relationship between climate and ice rheology at Dome C, East Antarctica: a comparison of fabric determined by borehole sonic logging and thin sections. |
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Conference - International - Communication |
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2011 |
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Vol. 13, EGU2011-2341, 2011 |
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Understanding past climate changes as recorded in annual layers within ice sheets is a societal and scientific priority. Oxygen isotopes from several deep ice-cores in Greenland and Antarctica have revealed oscillations with a 100 kyr periodicity extending back at least 740 kyr BP. The EPICA Dome C ice core, the longest climate record obtained from ice, records eight glacial-interglacial transitions where abrupt climate transitions typically separate warm periods (interglacial) from cool periods (glacial). These warm and cool periods are referred to as Marine Isotope Stages (MIS).
Many scientists have observed that the physical properties of glacial ice differs from those of interglacial ice. Glacial ice typically has smaller crystals, higher impurity content, and stronger fabric (preferred orientation of crystal c-axes). Because ice deformation is sensitive to the orientation of crystals, ice flow patterns are sensitive to the fabric and, therefore, to this glacial-interglacial dichotomy. Indeed at Dome C an abrupt, unexpected strengthening of the fabric at the depth of 1750 m marks the transition between the warm MIS5 and the cold MIS6. Because there is a positive feedback between fabric development and ice deformation, changes in ice fabric may be therefore used to understand climate transitions.
We present a vertical-profile of compressional (P) wave speeds acquired every 0.1m in the 3.2 km-deep EPICA Dome C borehole. Each measurements samples ice crystals within a volume approximately 3 m long and 2 m wide ice. We relate the P-wave speeds to fabric through the known seismic anisotropy of a single ice-crystals (P-wave speed is 5% faster when propagates along the crystallographic c-axis than the basal plane). We integrate this seismically-derived fabric profile with the more sparse (about 100 m for most of the core) thin-section-derived fabric to present a more complete vertical-profile of fabric. We provide a preliminary comparison of the shifts in fabric which occur at each of the abrupt climate transitions and relate these to other measurements made on the ice core and in the borehole such as dust and oxygen isotopes. |
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3592 |
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Landais A, Dreyfus G, Capron E, Pol K, Loutre M F, Raynaud D, Lipenkov V Y, Arnaud L, Masson-Delmotte V, Paillard D, Jouzel J, Leuenberger M, |
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Title |
Towards orbital dating of the EPICA Dome C ice core using δO2/N2
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2012 |
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Clim. Past |
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8 |
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1 |
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191-203 |
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902 |
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Copernicus Publications |
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1814-9332 |
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4152 |
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Picard G, Royer A, Arnaud L, Fily M, |
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Title |
Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica
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Journal Article |
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2013 |
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The Cryosphere Discuss. |
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The Cryosphere Discuss. |
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7 |
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4 |
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3675-3716 |
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902 |
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1994-0440 |
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4457 |
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G. Picard, M. Dumont, Q. Libois, L. Arnaud, S. Morin, M. Lafaysse, D. Voisin, C. Carmagnola |
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Conference - International - Communication |
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2013 |
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4461 |
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