Reconciling fundamental climate variables for determining the Antarctic Mass Balance

The Antarctic ice sheet is the largest ice sheet on Earth, it has the potential to raise the global mean sea level by 58 metres if it melts completely. Even though it is not the largest contributor to present-day sea level rise, recent studies have shown that the Antarctic ice sheet has increased its mass loss between 1993 and 2018. It is therefore important to monitor and understand how the ice sheet evolves to understand present and future rates of sea level rise.

This Ph.D. thesis focuses on reconciling climate variables to estimate the surface mass balance and the total mass balance of Antarctica. The surface mass balance is the sum of the accumulation (snowfall and rainfall), and the ablation (sublimation, evaporation, and runoff). Total mass balance includes both SMB and the discharge across the grounding line. In this thesis, a regional atmospheric climate model is used to model the atmosphere and the output used to compute the surface mass balance. To get a realistic representation of the subsurface snow and ice layers, a firn model has also been developed for the Antarctic ice sheet. This thesis investigates the uncertainties in modelled mass balance from different regional climate models and different methods. There are three geodetic methods to derive the mass balance from remote sensing; altimetry, mass budget, and gravimetric measurements. Two of these, altimetry and mass budget, require knowledge of the firn pack over the ice sheet. When using the mass budget method to estimate the mass balance the surface mass balance and the discharge values are need. The surface mass balance is here found to be  1968.0±279.3 Gt year-1 over the grounded part of Antarctica and over the total Antarctic ice sheet it is 2574.4 Gt year-1 from the period 1979 to 2021.

Applying the altimetry method, the satellite ICESat-2 has been used to measure the surface elevation change. To isolate the surface elevation change, that is due the ice dynamics, we have to correct for the firn compaction rate, for which we use the firn model, and correct for the vertical bedrock movement. When we have corrected for the nonice dynamic signals we can convert the volume change to mass change if the correct conversion density is known. This thesis therefore also presents new work for determining the appropriate density parametrization to be able to make a realistic conversion from volume change to mass balance change of the Antarctica ice sheet between 2018 and 2021. Finally, this thesis also shows some results for the Greenland ice sheet to show the applicability of the methods of this thesis for both ice sheets.