The state and fate of the Antarctic firn layer: a modelling and machine learning study

Abstract

The Antarctic ice sheet contains about 70% of the Earth's freshwater, making it the largest freshwater reservoir on the planet. If only 10% of the ice sheet were to melt, it would raise global sea level by approximately 6 m. Currently, mass loss from the Antarctic ice sheet is the largest source of uncertainty in sea level rise projections. To reduce this uncertainty, it is important to enhance our understanding of ice-sheet processes. A key component of the ice sheet is firn, which is the transitional material between snow and ice. Firn covers nearly all the ice sheet as a thick protective blanket, with a thickness up to 100 m. This firn layer acts as a sponge, as it provides pore space, in which currently most of the surface meltwater refreezes. Depletion of the firn pore space can lead to meltwater ponding at the ice sheet surface. This poses a risk, particularly for ice shelves, the floating extensions of the ice sheet that fringe 75% of Antarctica’s coastline. When conditions are unfavorable, meltwater ponding can lead to hydrofracturing and subsequent ice-shelf disintegration. Given that many ice shelves buttress the flow of grounded ice, their collapse can trigger accelerated mass loss from the Antarctic ice sheet. In my thesis, I study the contemporary and future state of the Antarctic firn layer, and develop and improve the methods for its simulation. My main tool is the firn densification model IMAU-FDM. To improve and evaluate the model, I use in-situ and remote sensing measurements. To explore future firn evolution for a broad range of climate scenarios, I also developed a computationally efficient machine learning emulator.