Present and future Ross Ice Shelf dynamics from observations and modelling, and implications for the Antarctic Ice Sheet

In recent decades, global warming has driven significant mass losses across the Antarctic Ice Sheet (AIS). Global warming of 1.5◦C and 2◦C is expected to be exceeded in the coming decades, which will trigger further AIS instabilities (Pattyn et al., 2018; Pörtner et al., 2022). The AIS has the potential to be the largest contributor to global sea level rise; thus, it is essential to understand the dynamics of the AIS in a warming world to aid governmental policies. The most significant mass losses in the AIS are driven by ocean-forced basal melting reducing the buttressing ability of ice shelves. The Ross Ice Shelf (RIS) is the largest cold water ice shelf on the AIS and buttresses the West and East Antarctic Ice Sheet. Understanding the current dynamics of the RIS in a warming world is important as the ice shelf has a large control over the mass balance of the AIS. Seasonal changes in sea ice cover have recently been found to elevate basal melt rates at the calving front of the RIS (Stewart et al., 2019). This thesis sets out to understand the influence of short-term environmental variability on RIS flow dynamics. This will be achieved through observing the RIS flow rates over seasonal and interannual timescales using GNSS and remote sensing methods. Exploration of environmental drivers of the observed flow variability is carried out using the Ice-sheet and Sea-level System Model (ISSM). Furthermore, ISSM is used to quantify sensitive areas of the RIS to changes in glaciology and environmental controls. The results showed that the RIS flow rates do not vary significantly on seasonal or interannual timescales, suggesting that the RIS dynamics are insensitive to external forcings at seasonal and interannual frequencies. However, basal melting was found to drive seasonal variations in ice flow dynamics with similar patterns to the GNSS velocities. The sensitivity maps highlighted that changes in basal melt in sensitive areas (i.e., grounding lines and shear margins) would impact the mass balance substantially and should be monitored in a warming world. The simulations could not replicate the observed velocity variations suggesting that some other environmental forcing not considered is driving these variations. Projections of the RIS and AIS using a range of climate models and present-day basal melt conditions were also performed in ISSM to understand whether short-term basal melt variability should be included in projections and the influence basal melt parameterisation inputs have on the final projected sea level contribution. The results showed that including short-term basal melt variability was not needed to project the mass changes of the RIS, with variability in surface mass balance driving larger changes in the mass balance over a 100 year timescale. However, using high spatio-temporal resolution datasets within the basal melt parameterisation projected larger basal melt rates, mass loss and sea level contributions for the AIS. Thus, uncertainties still exist in ice sheet modelled projections of sea level rise estimates, and policymakers should use multiple model simulations when planning adaptive strategies.