1. Ice motion at the Dome C ridge Luca Vittuari E-mail: luca.vittuari@mail.ing.unibo.it DISTART – University of Bologna - Italy

2. Material This presentation shows data and results acquired in the framework of EPICA, ITASE, TALDICE and VLNDEF Projects. … more details can be found in: Capra. A., R. Cefalo, S. Gandolfi, G. Manzoni, I.E. Tabacco, L. Vittuari. 2000. Surface topography of Dome Concordia (Antarctica) from kinematic interferential GPS and bedrock topography. Annals of Glaciology, 30, 42-46. Geodetic and geophysical observations in polar regions - Overview in IPY perspective, Editors: A. Capra, R. Dietrich, Springer (book in preparation). Urbini S., Frezzotti M, Gandolfi S., Vincent C., Scarchilli C., Vittuari L., Fily M. Historical behaviour of Dome C and Talos Dome (East Antractica) revealed by snow accumulation and ice velocity measurements. Submitted to Global and Planetary Change. Vittuari L., C. Vincent, M. Frezzotti, F. Mancini, S. Gandolfi, G. Bitelli, A. Capra. (2004). Space Geodesy as a tool for measuring ice surface velocity in the Dome C region and along the ITASE traverse. Annals of Glaciology. vol. 39, pp. 402 - 408.

3. Movements at Dome C ? Due to: - Continental drift - … - Ice surface topography - Glaciological hystory of the Dome behavior With respect to: - A Terrestrial Reference Frame (E.G. ITRF2000, ITRF2005,..) Measured: -Trhough integrated geodetical, geophysical and glaciological surveys

4. Influence of ice surface topography -Elliptical shape -Major axis SW-NE -Minor axis NW-SE 70% shorter -Elongation is parallel to the prevalent wind direction (SW-NE) -Snow-radar shows an increase of snow accumulation South-North Contours interval 25 cm 50 km

6. Influence of ice surface topography A GPS geodetic network composed of 37 points was established in 1995. It is composed of four concentric rings at increasing distances from the centre (approximately located at the drilling site), at 3, 6, 12.5 and 25 km respectively Surveyed twice (95/96 and 98/99)

7. Influence of Ice surface topography In order to describe relative movements, a six-parameter similarity transformation was applied to GPS network solutions.

8. In 1999 we estimated at EPICA drilling site, positioned between points E10 and E14, an interpolated relative velocity of about 15 mm/yr ±10mm/yr in a N-NW mean direction between E10, E14: 302°N. The other poles move at radial velocities of up to 211 mm/yr ±7mm/yr, with iso-values forming concentric ellipses, similar to the contour lines. All network’s points show a vertical velocity of about 90÷100mm/yr ± 9 mm/yr Influence of Ice surface topography

9. Glaciological hystory of the Dome behavior Snowfall trajectory and its interaction with orography is the main accumulation factor at Dome C. Through 500 km of snow-radar profiles and sixteen firn cores, was observed that accumulation in the past is non symmetrical with respect to the dome morphology. At Talos Dome five repeatitions of GPS measurements during last ten years have highlighted changes in ice velocity, apparently correlated with change in accumulation distribution. At TD repeated GPS revealed variations in velocities in the range -5 ÷ +4 mm/yr 2, while in DC this effect is unknown.

10. Absolute movement at continental scale The results obtained by SCAR GPS Epoch campaigns have highlighted a major clockwise motion of Antarctica, somewhere greater than 1 cm/yr (Dietrich et al. 2001) TNB1 – GPS permanent station installed at Mario Zucchelli Station. The observations performed at TNB1 span, almost continuously, a seven year period: from 1999 till 2006. Continental drift (I)

11. So if we consider this effect as mainly induced by a motion of the continent as a whole, the Euler Vector computed by Nuvel-1A NNR model, relating stable Antarctic Plate (ANTA) with respect to ITRF2000 (Altamimi et al. 2002) pointing out the following waited velocity at the position of Station Concordia: ModelLatitudeLongitude VELOCITY mm/yr Azimuth N Vel. mm/yr E Vel. mm/yrPlate ITRF20075° 6' 4" S123° 20' 52" E11.42172°-11.301.64ANTA The relative motion between the Antarctic Peninsula area and the eastern Antarctica is not larger than 1-2 mm/yr (Dietrich et al. 2004). Continental drift (III)

12. V Up = -152.6 mm/yr ± 1.3 mm/yr GPS observation acquired in the period 2-8 march 2007 and supplied by the winter-over personnel (Pietro Di Felice) V North = 5.8 mm/yr ± 0.4 mm/yr V East = -9.2 mm/yr ± 0.4 mm/yr GPS-derived “absolute” velocities of point DCRU expressed in a local geodetic system (N, E, U)

13. Movement with respect to ITRF2000 at DCRU Hor. 10.9 mm/yr ± 0.6 mm/yr azimuth 302° Vert. -152.6 mm/yr ± 1.3 mm/yr 10.9 mm/yr ± 0.6 mm/yr azimuth 302° The new measure carried-out at DCRU confirms the value estimated at EPICA location in 1999: 15±10 mm/yr with azimuth 302°

14. Conclusion and outlook -GPS measurements indicate that the DC summit move up to few mm/yr horizontally and up to 9-10 cm in vertical direction. At this level of resolution, absolute and relative measurements of ice surface velocity must be constrained to GPS long time series in order to reach the maximum reliability -GPS located on the roof of the noisy building has proven the capability of GPS to acquire during the winter at Dome C, opening the possibility of installation of a permanent station on the Antarctic plateau -In order to study the effects induced by the spatial variability in snow accumulation, non symmetric with respect to dome morphology, it is required a wider analysis that include repetition of GPS measurements on the strain network for long periods -To preserve the use of the GPS strain network installed at Dome C, extensions to network poles must be added before snow accumulation completely cover the poles heads - To avoid local effects induced by the buildings structure, the GPS permanent station has to be designed and installed on a submerged velocity system “coffee-can” powered by Station Concordia