Application of bedrock elastic deformation data to study meltwater transportation in Greenland

Le résumé fourni par la source

For the first time, we apply bedrock elastic deformation data to study meltwater transportation within the Greenland Ice Sheet (GrIS). We consider the vertical component of the deformations extracted from GPS data records acquired by the Greenland GNSS Network (GNET) stations. Data time-series from 22 stations distributed along the entire Greenland coast are analyzed. Various geophysical models are used to eliminate nuisance signals from the data. This concerns, among others, deformation associated with surface mass balance (SMB) processes. To quantify the effect of SMB processes, we use the estimates produced by regional climate models, such as RACMO2.3p2. The residual vertical deformations remaining after the subtraction of nuisance signals are fit to a simple analytic model, which allows us to quantify some parameters associated with buffered water storage (i.e., the temporal storage of meltwater on its way to the ocean). Among others, we quantify the average water storage time per station. We find that the average water storage time in Greenland is about 8 weeks. It is slightly larger along the northeast (9±2 weeks) and west (9±3 weeks) coasts. For the southeast coast, it is roughly halved (4.5±2 weeks). This is likely because the ablation zone in the southeast is relatively narrow and steep. Furthermore, we find that the water runoff estimated by regional climate models may require a down- or up-scaling, with the scaling factors being correlated with summer temperature anomalies. In the warmest summers the required runoff upscaling may reach 20%. Likely explanations are an underestimation of water melt or an overestimation of water retention in the firn (or both). The latter can happen if the model underestimates degradation of firn storage capacity caused by a reduction in the pore space and formation of impermeable ice layers. The finding that current regional climate models may require an adjustment in instances of high summer temperature is highly important in view of the ongoing climate warming. Summer temperatures that are considered high nowadays may become normal in the near future. Our study paves the way for more realistic projections of future GrIS meltwater production and its contribution to global sea level rise. Our results have been recently published in Nature (https://doi.org/10.1038/s41586-024-08096-3).

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