Modelling Sea-Level Fingerprints of Glaciated Regions with Low Mantle Viscosity

Abstract

Sea-level fingerprints, the spatial patterns of sea level change resulting from rapid melting of glaciers and ice sheets, play an important role in understanding past and projecting future changes in relative sea level (RSL). Over century timescales, the viscous flow of Earth’s interior is a small component of the total deformation due to ice loading in most regions, so fingerprints computed using elastic Earth models are accurate. However, in regions where the viscosity is orders of magnitude lower than the global average, the viscous component of deformation can be significant, in which case it is important to consider models of viscoelastic deformation. There is evidence that the glaciated regions of Alaska, Western Canada and USA, and the Southern Andes are situated on top of mantle regions in which the local viscosity is several orders of magnitude lower than typical global mean values. The goal of this work is to determine the importance of viscous flow in computing RSL fingerprints associated with future ice mass loss from these regions. Version 5.0 of the Randolph Glacier Inventory is used to estimate the ice load distribution required for calculating sea-level fingerprints. For the glaciated regions that have lower than average viscosity, fingerprints were calculated using an elastic Earth model and a 3D viscoelastic model to quantify the influence of viscous flow on the predicted sea level changes. Using glacier mass loss values for the intermediate future climate scenario Representative Concentration Pathway (RCP) 4.5, the global sea level response was computed at 2100 CE relative to 2010 CE due to melting from all glacier regions. On comparing the results of the two models it was found that ice-load-induced viscous flow contributes significantly (more than a few cm) to the RSL fingerprints only in near-field regions. However, in these regions, the non-elastic contribution can be 10s of cm. For example, at Juneau, USA the elastic calculation gave relative sea level changes of ∼ −45 cm, compared to ∼ −120 cm based on the viscoelastic calculation.