Toward new maps of basal melt rate in Antarctic grounding zones through inverse modeling of tidal flexure with ICESat-2

Abstract

In Antarctica, the grounding line is the triple junction where ice meets ocean meets earth, and grounded ice sheets become floating ice shelves. In the past decade, the surrounding area, termed the grounding zone, has come to be recognized as one of the most dynamic and sensitive indicators of change in the Antarctic. Ice shelves float up and down on ocean tides, but in the grounding zone, the ice shelf is mechanically coupled to the upstream grounded ice and flexes rather than floats. Here, we develop an observationally-constrained inversion based on the tidal flexure of ice shelves and ICESat-2 laser altimetry data to make new estimates of ice thickness, ice thickness gradient, ice rheological properties, and ultimately, basal melt rate, in grounding zones of the two largest Antarctic Ice Shelves. We find that the effective Young’s modulus of ice varies significantly in space, both on and among ice shelves, and that estimates of ice thickness in the grounding zone made by assuming ice shelves are in hydrostatic equilibrium may locally underestimate ice thickness on the order of 10-15 percent. Further, we calculate basal melt rate near the grounding line based on conservation of mass and find that ice thickness gradient is a first-order control on the spatial variation of basal melt rate, and using a flexure-inferred versus hydrostatically-inferred ice thickness requires differing interpretations of the oceanographic context close to the grounding line. As basal melt rate is one of the single greatest sources of uncertainty in modeling the rate and amount of future sea level rise from Antarctica, this may have far-reaching implications for ice sheet modeling.