Recent intercomparisons of ice sheet mass balance estimates derived from altimetry and from the input output method (IOM) have revealed significant discrepancies for the East Antarctic Ice Sheet. Modelled SMB, as a main input to the IOM, differs considerably between different models.

We explore comparisons between the altimetric mass balance method and the IOM for selected subregions of the Antarctic Ice Sheet. Rather than evaluating entire drainage basins, we aim at regions for which uncertainties in the horizontal mass flux through the region boundaries as well as in the altimetric mass balance are small. For this purpose, we choose subregions of the East Antarctic Plateau. We explore the hypothesis that this allows us to benchmark SMB modeling results in these regions, assuming that SMB is the most uncertain part in a comparison of net mass flux and altimetric mass change.

We apply the IOM using outputs from different SMB models (such as RACMO and MAR). We apply the altimetric method using different altimetric surface elevation change products (such as CryoSat2-AWI, and Multi-mission-JPL, ICESat-2-ATL-15) as well as firn air content changes from firn densification models (such as IMAU-FDM). We perform the evaluation for different regions with sizes ranging from about 6x104 to 1.5x102 km2 and for different time intervals, such as 1992-2019, or 2010-2019, or 2019-2024.

Discrepancies between the mass-flux-based IOM mass balance and the volume-based altimetric mass balance are significant for a number of regions, time intervals, and choices of input data product. The discrepancies are up to the order of some 10 percent of the SMB of the region. In particular, discrepancies (or their absence) are sensitive to input SMB modeling results. In the light of uncertainties assessed for all inputs, we discuss conclusions regarding the evaluation of SMB modeling results.