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Research School of Earth Sciences
Earth Physics

GPS Installation at Richardson Lake - Enderby Land, Antarctica

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Long-term changes in the Earth's gravity field recently estimated from space measurements through the Gravity Recovery and Climate Exmperiment (GRACE) have shown a large positive signal in Enderby Land between Mawson and Syowa. Chen et al. (2006) suggested "that this feature is either from unquantified snow accumulation in this region or more likely due to unmodelled postglacial rebound" (in other words, uplift of the Antarctic continent).








Richardson Lake, with Mt Riiser-Larsen in the foreground. The black line indicates the location of the GPS installation. Photo D. Zwartz

Long-term mass change rates (in units of cm/yr of equivalent water height) observed by GRACE. From Chen et al (2006). The new GPS site is located just above the cross "B".



In January 2007, a field party of geophysicists flew to Richardson Lake in Enderby Land, East Antarctica, to install a new remote GPS site to measure the vertical movement of the continent. The Australian Government Antarctic Division CASA aircraft landed on the permanently-frozen lake, close to suitable outcrops of solid bedrock on which the GPS antenna could be attached.

The GPS site was installed on 6 January 2007. GPS and system diagnostic data are transferred back to RSES via iridium satellite phone communications (as well as being stored on site).

The photos below were taken by Dr Dan Zwartz (RSES). Click on the photos to see the full-sized image.



Mt Riiser-Larsen.



Aerial view of Richardson Lake, with Mt Riiser-Larsen to the left and the peninsular on which the GPS site is installed to the top right. The sea ice can be seen in the distance on the horizon.



Location of the GPS site and the field camp. To the right of the GPS site is the frozen ice of Richardson Lake.



The new GPS antenna at site RICH. Power is generated by three solar panels (seen behind and to the left of the antenna). The field camp and casa aircraft can be seen in the background on the frozen lake.



The "office" is not too far away from the sleeping bag .......





Science Objectives

Geodetic estimation of Glacial Isostatic Adjustment

Long-term changes in the Earth's gravity field recently estimated from space measurements through the Gravity and Climate Exmperiment (GRACE) have shown a large positive signal in Enderby Land between Mawson and Syowa. Chen et al. (2006) suggested "that this feature is either from unquantified snow accumulation in this region or more likely due to unmodelled postglacial rebound" (in other words, uplift of the Antarctic continent). The anticipated rate of uplift is ~10 mm/yr.


Long-term mass change rates (in units of cm/yr of equivalent water height) observed by GRACE. From Chen et al (2006). The new GPS site is located just above the cross "B".


There are three possible causes of the observed signal:

    *Unmodelled Glacial Isostatic Adjustment. The melting of the Antarctic Ice Sheet since the Last Glacial Maximum (~20,000 years ago) has removed mass from the continent, which then rebounds. Imagine that there is cubic metre of ice sitting on the bow of a boat. The 1 tonne mass would make the boat sink lower in the water. When the ice melts, the boat will rise. The continents behave in a similar manner to the boat, with the mantle playing the role of the water.

    We would expect the new GPS installation to show a positive uplift rate, where the rate of rise of the continent provides information on the amount of ice that has melted.

    *Increased recent mass accumulation. GRACE senses changes in mass. If over the past 4 years there has been a progressive increase in snow/ice accumulation in the region then this would explain the signal detected by GRACE. In this case, the additional mass would cause subsidence of the continent, thereby producing a negative vertical velocity at the GPS site.

    *Errors in the GRACE analysis. One should never discount the possibility that the analysis of the GRACE data is in error and that the reported signal is an artifact of incorrect processing. If this is the case then there should be no (or very little) vertical movement detected at the GPS site.

Only in-situ observations can provide a ground truth for the GRACE results and this is the principal scientific goal of this experiment.



Contact Information:


Dr Paul Tregoning

Research School of Earth Sciences,
The Australian National University
 
Canberra, ACT 0200, AUSTRALIA

tel: +61-2-6125-5510
fax: +61-2-6125-5443
http://rses.anu.edu.au/~pault
Email: pault@rses.anu.edu.au
 
 
 
 


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