Achraf Koulali (Newcastle University, UK) and Matt King (University of Tasmania, Australia) will present:

“Sensitivity of Antarctic GPS time series to varying surface mass balance loads, and implications for estimates of Glacial Isostatic Adjustment”

Antarctic Global Positioning System (GPS) vertical time series exhibit non-linear signals across a wide range of temporal scales, complicating the interpretation of long-term deformation associated with Glacial Isostatic Adjustment (GIA). One important contributor to these non-linearities is the short-term elastic response of the solid Earth to contemporaneous surface mass balance (SMB) variability. During the first part of this talk, we will show analysis results of GPS vertical displacement time series from the Transantarctic Mountains (TAM) to quantify the impact of SMB-driven loading on observed crustal motion. SMBL-induced deformation is found to introduce multiyear apparent changes in vertical velocities. After correcting for SMB loading, most GPS sites exhibit near-zero uplift rates, with a median velocity of 0.67 mm/yr, substantially lower than predicted by forward GIA models. We will then discuss these results within the wider context of Antarctica to show the critical role of SMB loading variability in interpreting GPS observations more widely, with implications for estimates of present-day Antarctic ice mass change. As a second case study, we will discuss the sensitivity of GPS velocities to SMB variability in a critical sector of East Antarctica, including in the Denman-Totten glacier region, suggesting that bedrock motion in that region is broadly of subsidence rather than uplift in contrast to GIA models. Finally, we will show that modelled SMB variability can be compared with GPS elastic displacements across Antarctica, as a new form of SMB model validation.