Abstract
The surface mass balance (SMB) is very low over the vast East Antarctic Plateau, for example in the Vostok region, where the mean SMB is on the order of 20–35 kg m-2 a-1. The observation and modeling of spatio-temporal SMB variations are equally challenging in this environment. Stake measurements carried out in the Vostok region provide SMB observations over half a century (1970–2019). This unique data set is compared with SMB estimations of the regional climate models RACMO2.3p2 (RACMO) and MAR3.11 (MAR). We focus on the SMB variations over time scales from months to decades. The comparison requires a rigorous assessment of the uncertainty in the stake observations and the spatial scale dependence of the temporal SMB variations. Our results show that RACMO estimates of annual and multi-year SMB agree well with the observations. The regression slope between modelled and observed temporal variations is close to 1.0 for this model. SMB simulations by MAR are affected by a positive bias which amounts to 6 kg m-2 a-1 at Vostok station and 2 kg m-2 a-1 along two stake profiles between Lake Vostok and Ridge B. None of the models is capable to reproduce the seasonal distributions of SMB and precipitation. Model SMB estimates are used in assessing the ice-mass balance and sea-level contribution of the Antarctic Ice Sheet by the input-output method. Our results provide insights into the uncertainty contribution of the SMB models to such assessments.
Highlights
Regional climate models (RCMs) have evolved into valuable resources for the estimation of the components of the surface mass balance (SMB) over polar ice sheets
Over the Antarctic Ice Sheet (AIS) the SMB is dominated by snow precipitation, an order of magnitude larger than the other mass fluxes, while mass losses are dominated by sublimation of surface snow and drifting snow (Agosta et al, 2019)
Our comparison reveals a clear common signal in the SMB time series derived from stake observations and continentalscale atmospheric models
Summary
Regional climate models (RCMs) have evolved into valuable resources for the estimation of the components of the surface mass balance (SMB) over polar ice sheets. A reliable knowledge of the present-day SMB on the EAP is important to understand the extent to which the two proposed kinds of SMB induced surface elevation change signals could compensate dynamically induced AIS mass losses in the 21st century (Schlegel et al, 2018), and for validating paleo-runs of ice sheet models used for the interpretation of ice core data such as the Vostok ice core. The very low SMB calls for an accurate representation of all involved processes, requiring model parameters tuned to conditions substantially different from, and sometimes even in conflict with, those in the highly dynamic coastal zones more densely sampled by instrumental observations In this cold environment (mean surface air temperature: -54.9°C, Shibayev et al, 2019) surface melt is absent and the efficiency of the sublimation of both drifting snow and precipitating particles in low-level atmospheric layers is substantially reduced.
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