Surface mass balance of the Ross Ice Shelf from stable water isotopes, ground penetrating radar, and back trajectory analyses

Abstract

Precipitation in Antarctica, described by the surface mass balance (SMB), is the largest positive constituent of ice sheet mass balance, thus plays a key role in the Antarctic, hence global climate. Due to spatial and temporal scarcity of ground-based observations, there remain many unknowns about the precipitation regimes in Antarctica. This thesis investigates the temporal and spatial variability of SMB over a ~500km2 area near the middle of the Ross Ice Shelf (RIS), and explores the climatic and non-climatic controls behind displayed variability.

Annual net accumulation was determined by means of analysing seasonal variations in stable isotopes δ18O and δ2H from a 16m firn core. A 32 year time series was derived at annual resolution, representing average annual net accumulation of ~220 ± 100mm water equivalent (w.e.) yr-1 ‒ approximately double that of previous estimates. As the firn core was spatially limiting, the use of Ground Penetrating Radar (GPR) allowed for expanding the ground truth to a wider area.

~150km of GPR profiles were used to derive spatial variations in snow accumulation. Spatial variability was an order of magnitude smaller than temporal variability, and is likely controlled by active flow features on the ice shelf. These features can be traced back to the grounding line, and are likely preserved due to differential flow of the ice shelf. With temporal variability being far greater than spatial variability, an investigation into the climatic controls of precipitation was required.

To understand the climatic controls on temporal variations in net snow accumulation, an atmospheric back trajectory and cluster analysis was undertaken using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. A total of 20 distinct synoptic pathways were identified, with pathways originating in Ross Sea accounting for the majority of precipitation on the RIS. I find that the frequency of Ross Sea air mass trajectories is modulated by the El Niño-Southern Oscillation, represented by the Southern Oscillation Index (SOI), and suggest that both the SOI and back trajectory analyses show potential to be used as proxies for accumulation in this region.

Together, these studies form the basis and justification for future work in this region. They show that the current estimates of snowfall on the RIS may be largely underestimated, which has important implications for the input parameters of numerical models simulating the future behaviour of the Ross Ice Shelf.