Abstract
Abstract. Global patterns of sea-level change – often termed “sea-level fingerprints” – associated with future changes in ice/water mass re-distribution are a key component in generating regional sea-level projections. Calculation of these fingerprints is commonly based on the assumption that the isostatic response of the Earth is dominantly elastic on century timescales. While this assumption is accurate for regions underlain by mantle material with viscosity close to that of global average estimates, recent work focusing on the West Antarctic region has shown that this assumption can lead to significant error where the viscosity is significantly lower than typical global average values. Here, we test this assumption for fingerprints associated with glaciers and ice caps. We compare output from a (1D) elastic Earth model to that of a 3D viscoelastic model that includes low-viscosity mantle in three glaciated regions: Alaska, southwestern Canada, and the southern Andes (Randolph Glacier Inventory (RGI) regions 1, 2, and 17, respectively). This comparison indicates that the error incurred by ignoring the non-elastic response is of the order of 1 mm in most areas (or about 1 % of the barystatic signal) over the 21st century with values reaching the centimetre level in glaciated regions. However, in glaciated regions underlain by low-viscosity mantle, the non-elastic deformation can result in relative sea-level changes with magnitudes of up to several tens of centimetres (or several times the barystatic value). The magnitude and spatial pattern of this non-elastic signal is sensitive to variations in both the projected ice history and regional viscosity structure, indicating the need for loading models with high spatial resolution and improved constraints on regional Earth viscosity structure to accurately simulate sea-level fingerprints in these regions. The anomalously low mantle viscosity in these regions also amplifies the glacial isostatic adjustment signal associated with glacier changes during the 20th century, causing it to be an important (and even dominant) contributor to the modelled relative sea-level changes over the 21st century.
Highlights
A variety of processes drive changes in the vertical position of the ocean floor and ocean surface (e.g. Church et al, 2013; Milne et al, 2009), and the combination of these processes produces a complex pattern of relative sea-level (RSL) change that varies through time
Our goal is to quantify the signal of the non-elastic response to sea-level fingerprints computed for the three Randolph Glacier Inventory 5.0 (RGI) regions introduced above
The RSL differences are not as large as they are for Alaska because the amplitude of ice mass loss is lower (Fig. 1), but the differences still reach values of ∼ 10 cm and are large relative to the barystatic signal (10.8 cm)
Summary
A variety of processes drive changes in the vertical position of the ocean floor and ocean surface (e.g. Church et al, 2013; Milne et al, 2009), and the combination of these processes produces a complex pattern of relative sea-level (RSL) change that varies through time. As a result, predicting future sea-level changes at regional to local scales is challenging, as it requires calculating and summing signals associated with numerous physical processes that have a range of spatial scales and response times (Slangen et al, 2012; 2014; Kopp et al, 2014). The melting of ice sheets and glaciers produces a spatial pattern of sea-level change due to the resulting solid Earth deformation and changes to the geopotential (Farrell and Clark, 1976). When these changes happen on decadal to centennial timescales, the resulting solid Earth response is assumed to be dominantly elastic; the non-elastic (viscous) contribution is commonly neglected. These fingerprints play a central role in projections of regional sealevel change (Church et al, 2013; Oppenheimer et al, 2019; Palmer et al, 2020; Slangen et al, 2012, 2014; Spada, 2017)
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