Chia-Chun Liang Dissertation Defense

Title: Improving the Mass Balance of Antarctica and Its Sub-regions Using GRACE, GRACE-FO Satellites, and Other Data

Abstract: The Antarctic Ice Sheet, even though isolated from the rest of the world, is a major part of the Earth system. Antarctica is a major participant in the Earth’s energy budget, global hydrology cycle, ice-albedo feedback, and global ocean circulation, and is a natural indicator of climate change. The melting of ice directly influences global sea level, which in turn directly influences 40 percent of the world population living worldwide. According to IPCC6, the Antarctic Ice Sheet contributes to the largest uncertainty to projections of 21st-century global sea level. Hence a better quantification of the Antarctic mass balance, i.e. the evolution of ice sheet mass, is essential.

Since 2002, time-variable gravity data from the Gravity Recovery And Climate Experiment (GRACE) and Follow-On (GRACE-FO) have been used to retrieve the evolution of the Antarctic ice mass with precision and on a monthly basis. As an example, we will show the latest updated record of the mass budget of Antarctica for 2002-2024. The largest residual uncertainty in these estimates is the magnitude of the correction for the glacial isostatic adjustment (GIA), especially in East Antarctica (EAIS) because it has a lower level of observational constraints compared to West Antarctica (WAIS), and also because it experiences a much lower mass loss at present, such that the uncertainty in GIA represents a major fraction of the signal. The state-of-the-art GIA estimates are derived from forward modeling or Bayesian approaches, which are highly unconstrained in East Antarctica, with poorly documented errors.    

In this work, we propose a novel framework to estimate the uncertainty in GIA due to a lack of observational constraints which allows us to quantify unaccounted uncertainties in traditional methods in a rigorous fashion. We use time-variable gravity GRACE and GRACE-FO data combined with satellite altimetry data, and Global Positioning System (GPS) data, unified under an analytical framework defining the relationship between GIA, changes in gravity, surface elevation, and bedrock elevation. Prior work combining these data under a unified framework derived an empirical relationship; here, we derive an analytical relationship, of broader use, and with higher accuracy. Using that novel approach, we document that the uncertainty in the GIA in East Antarctica introduces an error of up to 40 Gigaton per year (Gt/yr) in mass balance. We also used this approach to quantify how new as well as existing GPS stations can help reduce these uncertainties and in turn, improve the mass balance estimates. Early results indicate that additional corrections on the GIA in East Antarctica will have a major impact on the resulting estimates of its state of mass balance.