Ice Caps and Water Resources Research at RSES

Changes in mass can be detected from space-gravity missions and provide key information on how polar ice caps are responding to present-day temperature changes and how continental water resources are varying. Under a warming climate scenario, increased precipitation is predicted for low-latitude zones while mid-latitude regions such as southeastern Australia will become drier.

Current Research projects

Variations in water resources in Australian drainage basins

With the onset of warmer global temperatures, an increase in precipitation is predicted for low-latitude regions of northern Australia, while the southern parts are predicted to become drier. Water is a critical resource, yet little is currently known about the actual amount of groundwater available, let alone how the resource is changing. The Gravity Recovery and Climate Experiment (GRACE) satellite mission began in 2002 and has a proven capacity to measure variations related to hydrological patterns. GRACE can generate estimates of mass variations which can be interpreted as the sum of ground water, soil moisture, surface and atmospheric water. Such information can provide data on water resources at the basin-scale, information that is not readily available at the present time.

To date, the capability of the GRACE mission has not been utilised to study the temporal variations in water resources in Australia. Before the results of the analysis of GRACE data can be used, the accuracy of the estimates must be quantified. How much "error" is introduced into the estimates of Australian drainage basins from the leakage of signal from real mass variations elsewhere in the world? What is the smallest drainage basin area that can be investigated in the Australian region, while still achieving estimates of sufficient accuracy to provide useful information? Which of the four international centres generating montly GRACE solutions is the most accurate for the Australian region?

A regional approach has significantly higher resolution than a spherical harmonic approach for detecting the crustal deformation after the 2004 Sumatra earthquake; therefore, it is likely to permit drainage basins of smaller area to be assessed separately. We intend to develop software to generate regional GRACE solutions for studying the Australian drainage basins.

Mass balance changes of polar ice caps

The ability to detect monthly mass changes through space-geodetic missions provides the capability to assess changes in the ice sheets of Antarctica and Greenland. Decreases in mass imply that the cryosphere is melting and increasing the volume of the oceans whereas increases in mass imply increased precipitation and snow accumulation. The contribution of ongoing isostatic adjustment to GRACE estimates of mass balance changes is significant - over 100% of the mass loss in the case of some reported values (Velicogna and Wahr, 2006). Nonetheless, space-geodetic techniques provide the most accurate information on polar melting that is currently available.

How fast are Antarctica and Greenland melting and how is such melting contributing to rising sea level? The total mass variation sensed by the satellites is the combination of isostatic adjustment, present-day melting, snow accumulation and variations in atmospheric pressure, atmospheric water vapour and ocean mass. Many of these are "removed" using global and/or incomplete models with deficiencies either known, suspected or unquantified. Research is underway to understand the accuracy limitations of the techniques and how to improve them.

Present-day Glacial Isostatic Adjustment of Antarctica

Changes in mass balance (or the amount of ice that has melted) can be measured using space-geodetic techniques that detect variations in the Earth's gravity field and changes in ice height. Both satellite altimetry (used to measure ice topography heights) and GRACE (measures changes in potential) are sensitive to ongoing changes in continental lithosphere from glacial isostatic adjustment, the visco-elastic response of the Earth to the removal of a load after significant ice sheet melting over the past 10,000 years.

The rate of present-day uplift can be estimated using data from permanent GPS installations in Antarctica and can provide constraints on the modelling of the timing and amount of ice that has melted. Since 1998, RSES has installed and operated a network of remote GPS sites in East Antarctica specifically to estimate the isostatic adjustment pattern in the region. Uplift rates are significantly lower than anticipated, implying that either less ice has melted than is incorporated in the glaciology models or that the melting process ended earlier than expected.

Cosmogenic exposure dating utilises the amount of bombardment of cosmic particles that rocks have undergone to calculate when the rocks were exposed to the atmosphere. This provides constraints on the retreat of ice sheets. Coupled with dating of raised marine platforms, lake sediments and biological samples, past ice histories can be reconstructed to generate predicted present-day uplift scenarios that can be compared to observed uplift rates from GPS.