Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications

Abstract

S U M M A R YIn the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.The derived ice flow velocity for Vostok Station is 2.00 m a −1 ± 0.01 m a −1 . Along the flowline of Vostok Station an extension rate of about 10 −5 a −1 (equivalent to 1 cm km −1 a −1 ) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a −1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.

Observational evidence on the stability of the hydro‐glaciological regime of subglacial Lake Vostok

“…With the present study we extend our understanding based on own previous investigations on Lake Vostok [ Wendt et al , 2005; Masolov et al , 2006; Wendt et al , 2006; Roemer et al , 2007]. Here we present new results obtained from joint geodetic‐geophysical field measurements in the area of Vostok station taken in January 2007.…”

“…the fit of a linear trend. A more detailed description of the analysis approach and the error estimation is given by Wendt et al [2006]. For the seven markers, ellipsoidal coordinates, the velocity components and their accuracies are given in Table 1.…”

“…A strain analysis was performed in order to derive the deformation status of the internal geometry of the hexagon (Figure 1b). For this purpose, the horizontal velocities of the seven markers were introduced into a common adjustment algorithm yielding the strain parameters and the orientation of the principal strain axes (for methodological details see [ Wendt et al , 2006]). We obtained a maximum extension of 8.07 ± 0.42 10 −6 yr −1 along an azimuth of 109°.…”

“…The rate of basal ice accretion along the flowline crossing Vostok station was estimated based on the detection and observation of the thickness of the accreted ice layer by airborne RES and the ice flow velocity determined by GPS [ Bell et al , 2002]. Wendt et al [2006] recalculated the accretion rate for the flowline segment 26 km upstream from Vostok station using significantly improved values for the ice flow velocity, which also account for the acceleration across the lake. Flow velocity and distance were inverted into the travel time of the ice sheet along the flowline segment with a relative error of 10% [ Wendt et al , 2006].…”

Precise analysis of ICESat altimetry data and assessment of the hydrostatic equilibrium for subglacial Lake Vostok, East Antarctica

“…However, such small‐scale surface features are below the spatial resolution of the GLAS data. The markers were observed by GPS during the Antarctic field seasons between 2001 and 2008 with observation times ranging from several hours to 10 days (Wendt et al 2006; Richter et al 2008). The GPS data were processed using the Bernese GPS software 5.0 (Dach et al 2007) yielding 3‐D site coordinates.…”