What is the surface mass balance of Antarctica?

This study estimates the surface mass balance (SMB) of Antarctica, by making an intercomparison of five different regional climate models (RCMs) all simulating the Antarctic climate from 1987-2015. This study was led by Dr. Ruth Mottram from DMI and was a collaboration between several European institutes in Antarctic research, amongst other DTU Space and DMI, the study was published in The Cryosphere

The SMB is the sum of accumulation and ablation on an ice sheet surface. Accumulation is precipitation, which in Antarctica is primarily snowfall, and ablation consists of sublimation, evaporation, and runoff.

Our research shows that, when RCMs are forced by the ERA-Interim reanalysis data set, the integrated Antarctic ice sheet ensemble mean annual SMB is 2329 ± 94 Gigatonnes (Gt) per year. However, individual model estimates vary from 1961±70 to 2519±118 Gt per year, this spread corresponds to approximately 2 mm of global sea level per year. The large differences are mostly explained by different SMB estimates in West Antarctica and over the Antarctic Peninsula. Integrated over the continent all the RCMs show a consistent interannual variability, which is strongly correlated with the forcing data ERA-interim. In the interior of East Antarctica, the annual mean SMB is below 25 mm of water equivalent per year, in West Antarctica, it is greater than 1500 mm water equivalent per year. To evaluate the individual model performances of simulating near-surface climate, we have used in situ measurements of near-surface temperature, firn temperature, surface pressure, wind speeds, and SMB measurements. No one model outperforms the others, the models have different strengths and weaknesses for different variables in different regions. However, in areas with complex topography, e.g in West Antarctica and the Antarctic Peninsula the resolution of the models is extremely important, the higher resolution is, the better the topography is resolved, leading to changes in orographic precipitation and katabatic winds.

Annually resolved SMB integrated over the entire ice sheet for the different RCMs, in the period 1979-2018. All RCMs are driven by ERA-Interim and except for MARv3.10 and RACMO2.3p2, SMB is calculated according to Equation 1. The ensemble is a mean calculated from all 6 RCMs in the period 1987-2015 where there is data from all the models. All trend lines are calculated for the period 1987-2015.

Sub-figure a show the SMB ensemble mean for the common period. Sub-figure b-g shows the difference between each model and the ensemble mean.

Full study:
Mottram, R., Hansen, N., Kittel, C., van Wessem, M., Agosta, C., Amory, C., Boberg, F., van de Berg, W. J., Fettweis, X., Gossart, A., van Lipzig, N. P. M., van Meijgaard, E., Orr, A., Phillips, T., Webster, S., Simonsen, S. B., and Souverijns, N.: What is the Surface Mass Balance of Antarctica? An Intercomparison of Regional Climate Model Estimates, The Cryosphere, https://doi.org/10.5194/tc-15-3751-2021