Net mass balance calculations for the Shirase Drainage Basin, east Antarctica, using the mass budget method

We quantify the mass budget of the Shirase drainage basin (SHI), Antarctica, by separately estimating snow accumulation (surface mass balance; SMB) and glacier ice mass discharge (IMD). We estimated the SMB in the SHI, using a regional atmospheric climate model (RACMO2.1). The SMB of the mainstream A flow region was 12.1 ± 1.5 Gt a−1 for an area of 1.985 × 105 km2. Obvious overestimation of the model round the coast, ∼0.5 Gt a−1, was corrected for. For calculating the IMD, we employed a 15-m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with a digital elevation model (DEM) to determine the heights at the grounding line (GL), after comparison with the interpolated Bamber DEM grid heights; the results of this are referred to as the measured heights. Ice thickness data at the GL were inferred by using a free-board relationship between the measured height and the ice thickness, and considering the measured firn depth correction (4.2 m with the reference ice density of 910 kg m−3) for the nearby blue-ice area. The total IMD was estimated to be 14.0 ± 1.8 Gt a−1. Semi-empirical firn densification model gives the estimate within 0.1–0.2 Gt a−1 difference. The estimated net mass balance, –1.9 Gt a−1, has a two-σ uncertainty of ±3.3 Gt a−1, and probable melt water discharge strongly suggests negative NMB, although the associated uncertainty is large.