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Lefebvre, E. Ritz, C, Legrésy, B., and Possenti, P. |
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New temperature profile measurements in the EPICA Dome C borehole EGU, 2008, Vienne Autriche |
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Conference - International - Poster |
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2008 |
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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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626 |
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Legresy, B., S. Zhang, R. Hurd, P. Lacroix and R. Coleman. |
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Snow surface roughness at Dome C, Antarctica. |
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2010 |
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IPY conference, OSLO, june 2010. |
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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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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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Marine Isotope Stage 19 (MIS 19) is the oldest interglacial period archived in the EPICA Dome C ice core (~ 780 ky BP) and the closest “orbital analogue” to the Holocene -- albeit with a different obliquity amplitude and phase with precession. New detailed deuterium measurements have been conducted with a depth resolution of 11 cm (corresponding time resolution of ~ 130 years). They confirm our earlier low resolution profile (55 cm), showing a relatively smooth shape over the MIS 20 to MIS 18 time period with a lack of sub-millennial climate variability, first thought to be due to this low resolution. The MIS 19 high resolution profile actually reveals a strong isotopic diffusion process leading to a diffusion length of at least ~ 40 cm erasing sub-millennial climate variability. We suggest that this diffusion is caused by water-veins associated with large ice crystals at temperatures above -10 °C, temperature conditions in which the MIS 19 ice has spent more than 200 ky. This result has implications for the selection of the future “oldest ice” drilling site.
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0012-821X |
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2009 |
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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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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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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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AGU |
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0148-0227 |
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505 |
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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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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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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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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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Based on a composite of several measurement series performed on ice samples stored at -25 °C or -50 °C, we present and discuss the first δO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at -25 °C show clear gas loss affecting the precision and mean level of the δO2/N2 record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off, and δO2/N2 in air bubbles, from which orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering, and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC. Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between δO2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO2/N2 record (and vice versa). Recognizing these limitations, we restrict the use of our δO2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300–800 ka period. |
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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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Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica
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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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Space-borne passive microwave radiometers are widely used to retrieve information in snowy regions by exploiting the high sensitivity of microwave emission to snow properties. For the Antarctic Plateau, many studies presenting retrieval algorithms or numerical simulations have assumed, explicitly or not, that the subpixel-scale heterogeneity is negligible and that the retrieved properties were representative of whole pixels. In this paper, we investigate the spatial variations of brightness temperature over a range of a few kilometers in the Dome C area. Using ground-based radiometers towed by a vehicle allowing measurements with meter resolution, we collected brightness temperature transects at 11, 19 and 37 GHz at horizontal and vertical polarizations. The most remarkable observation was a series of regular undulations of the signal with a significant amplitude of up to 10 K at 37 GHz and a quasi-period of 30–50 m. In contrast, the variability at longer length scales seemed to be weak in the investigated area and the mean brightness temperature was close to AMSR-E and WindSat satellite observations for all the frequencies and polarisations. To establish a link between the snow characteristics and undulation-scale variations of microwave emission, we collected detailed snow grain size and density profiles to run the DMRT-ML microwave emission model at two points where opposite extrema of brightness temperature were observed. The numerical simulations revealed that the difference in density of the upper first meter of the snowpack explained most of the brightness temperature variations. In addition, we found in the field that these variations of density were linked to the hardness of the snowpack. Areas of hard snow – probably formed by the wind – were clearly visible and covered as much as 39% of the investigated area. Their brightness temperature was higher than in normal areas. This result implied that the microwave emission measured by satellites over Dome C is more complex than expected and very likely depends on the areal proportion of the two different types of areas having distinct snow properties. |
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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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Evolution of the profile of absorbed energy in the Alpine snowpack: extinction measurements and improvement of Crocus model´s optical scheme.
Davos Atmosphere and Cryosphere Assembly, Davos, 2013 |
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2013 |
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4461 |
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