Role of Glacial Isostatic Adjustment Process in the Present-Day Sea-Level Budget Closure

Global sea-level rise under anthropogenic warming is a significant societal problem. The ultimate goal is to understand the mechanisms of geophysical sources contributing to sea-level rise, to enable more accurate projection of 21st Century sea-level rise. One or multiple post-2007 IPCC Fourth Assessment Report sea-level budget assessment studies indicated that circa 50-70% of the observed sea-level rise of ~2 mm/yr remains unexplained. This surprisingly large present sea-level budget discrepancy is perhaps attributable to the wide range of estimates of land water contribution to present-day sea-level rise: from rapidly ablating mountain glaciers, ice-sheets, and potentially other sources including abyss ocean steric sea-level rise and imperfect knowledge of the Glacial Isostatic Adjustment (GIA) process resulting from deglaciation of Pleistocene ice-sheets or from the Little Ice Age. Despite of the recent publications on the closure of the ocean mass sea level budget, comparing steric-corrected altimetry sea-level rise with the independent GRACE estimated ocean mass variations or ocean bottom pressure changes, we find that the errors in the GIA forward model still limit the budget closure. GIA is not separable from the observed ocean mass variation signals, if GRACE is the only data type used and an accurate GIA forward model is unavailable. Here we study the feasibility on the use of GRACE, satellite radar altimetry, Argo and other hydrographic data, towards constraining the current knowledge of the ocean mass variations of the present-day sea-level budget. Our focus is to more exactly quantify the errors in the currently available GIA models with the goal of achieving the sea-level budget closure.