Historical behaviour of Dome C and Talos Dome (East Antarctica) as investigated by snow accumulation and ice velocity measurements

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Abstract

Ice divide–dome behaviour is used for ice sheet mass balance studies and interpretation of ice core records. In order to characterize the historical behaviour (last 400 yr) of Dome C and Talos Dome (East Antarctica), ice velocities have been measured since 1996 using a GPS system, and the palaeo-spatial variability of snow accumulation has been surveyed using snow radar and firn cores. The snow accumulation distribution of both domes indicates distributions of accumulation that are non-symmetrical in relation to dome morphology. Changes in spatial distributions have been observed over the last few centuries, with a decrease in snow accumulation gradient along the wind direction at Talos Dome and a counter-clockwise rotation of accumulation distribution in the northern part of Dome C. Observations at Dome C reveal a significant increase in accumulation since the 1950s, which could correlate to altered snow accumulation patterns due to changes in snowfall trajectory. Snow accumulation mechanisms are different at the two domes: a wind-driven snow accumulation process operates at Talos Dome, whereas snowfall trajectory direction is the main factor at Dome C. Repeated GPS measurements made at Talos Dome have highlighted changes in ice velocity, with a deceleration in the NE portion, acceleration in the SW portion and migration of dome summit, which are apparently correlated with changes in accumulation distribution. The observed behaviour in accumulation and velocity indicates that even the most remote areas of East Antarctica have changed from a decadal to secular scale.

Introduction

One of the most extreme environments on the Earth's surface is the ice divide extending from Dronning Maud Land (DML) to Talos Dome (TD) in inner East Antarctica (Fig. 1). Due to extremely difficult field conditions in the inner part of East Antarctica, the accumulation pattern and evolution of the dome–ice divide is poorly known. The Earth's oldest ice cores were obtained along or near this ice divide (EPICA DML, Dome Fuji, EPICA Dome C, Vostok). Dome C (DC), Antarctica's fourth highest dome (3233 m), is about 1200 km from the Southern Ocean. The French–Italian Concordia Station (123°20′52″E, 75°06′04″S), where the EPICA (European Project for Ice Coring in Antarctica) drilling site is located, is about 1.4 km west of the DC surface summit. TD is an ice dome on the edge of the East Antarctic plateau (159°04′21″E, 72°47′17″S; 2318 m), about 1100 km East of DC (Fig. 1) and about 280 km from the Southern Ocean and Ross Sea.

In December 2004 a 3270 m deep ice core was recovered at DC within the framework of EPICA. This core provides the oldest existing ice climate record, extending to 740,000 yr before the present (EPICA community, 2004). In 2004, a new ice coring project, TALDICE (Talos Dome Ice Core Project), was started at TD with the aim of recovering 1550 m of ice that spans the last 120,000 yr (Frezzotti et al., 2004a). Ice divide–dome migration cannot be directly detected. However, the stability of the dome and position of the ice divide must be known in order to accurately interpret ice core records and to complete ice sheet mass balance studies. Models of depth–age relations for deep ice cores are sensitive to migration of the dome position (Anandakrishnan et al., 1994). Ice divide migration is also important in determining the input parameter of large Antarctic drainage basins. The behaviour of an ice divide is driven by its accumulation rate history and spatial pattern and conditions at ice sheet boundaries (e.g. Hindmarsh, 1996, Nereson et al., 1998, Frezzotti et al., 2004a). Indeed, surface elevations at DC, Vostok and Dome Fuji have varied by up to 100–150 m between glacial and interglacial periods due to changes in accumulation (Ritz et al., 2001).

The low slope (less than 1 dm per km) of the East Antarctic domes and their surface morphology at meter scale (e.g., sastrugi) makes it very difficult to determine the summit point of the dome and its migration over time.

The objective of this paper is to provide information on the historical behaviour of DC and TD using snow accumulation distribution during the last 400 yr as revealed by detailed snow accumulation, radar derived isochrones and ice dynamic changes based on ice velocity measurements made over the last 10 yr.

These data should be very useful in the future for determining changes in mass balance and thickness in these areas and detecting the possible impact of climate change to the ice core. DC and TD are also interesting sites for comparisons with satellite observations and numerical modelling.

Section snippets

Materials and methods

Internal layers of strong radar that are reflectively observed with Ground Penetrating Radar (GPR) are isochronous, and surveys along continuous profiles provide detailed information on spatial variability in snow accumulation (e.g., Richardson et al., 1997, Vaughan et al., 1999, Frezzotti et al., 2002, Eisen et al., 2004, Spikes et al., 2004, Frezzotti et al., 2005). For the purposes of this study, sixteen shallow snow–firn cores were drilled in the DC area and six in the TD area (Vincent and

Talos Dome

Based on the depth distribution of snow layers, Frezzotti et al., 2004a, Frezzotti et al., 2007) found that accumulation decreases downwind of TD (N–NE) and is higher in the SSW sector (Fig. 3). TD surface contour lines are elliptical and elongated in a NW–SE direction; the NW and NE slopes are steeper. The elongation direction of the dome is perpendicular to the prevalent wind direction and parallel to both the outcropping Outback Nunataks (50 km North to TD) and the sharp NW–SE ridge in the

Conclusions

The accumulation map obtained from snow radar data reveals a significant spatial variability in the snow accumulation rate at Talos Dome and Dome C. Accumulation distributions are not symmetrical in relation to dome morphology, and the accumulation distribution pattern has changed over the last few centuries. At Talos Dome the accumulation value for the period 1835–1920 AD is significantly lower than the values for the previous (1635–1835 AD) and subsequent (1920–2001 AD) periods in the SW

Acknowledgements

Research was carried out in the framework of the Project on Glaciology of the PNRA-MIUR and was financially supported by the PNRA Consortium through collaboration with ENEA Roma. This paper is a French–Italian contribution to the ITASE and Concordia Station projects and the EPICA and TALDICE projects. EPICA is a joint ESF (European Science Foundation)/EU scientific programme funded by the European Commission and by national contributions from Belgium, Denmark, France, Germany, Italy, the

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