Abstract: 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

Abstract: 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.

Abstract: 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.

Abstract: 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.