Modelling sea-level fingerprints of glaciated  regions with low mantle viscosity

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.

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Modelling sea-level fingerprints of glaciated regions with low mantle viscosity

10.5194/esd-2020-72 ◽

2020 ◽

Author(s):

Alan Bartholet ◽

Glenn A. Milne ◽

Konstantin Latychev

Keyword(s):

Sea Level ◽

Viscoelastic Model ◽

Elastic Response ◽

Earth Model ◽

Southern Andes ◽

Ice Caps ◽

Spatial Gradients ◽

Elastic Earth ◽

Low Viscosity ◽

Spatially Varying

Abstract. Sea-level fingerprints define the spatially varying relative sea-level response to changes in grounded ice distribution. These fingerprints 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 time scales. While this assumption is accurate for regions underlain my mantle material with viscosity close to that of global average estimates, recent work focusing on the Antarctic region has shown that this assumption can led to significant error when the viscosity departs significantly from typical 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 which includes low viscosity mantle in three glaciated regions: Alaska, southwestern Canada and the southern Andes (Randolph Glacier Inventory (RGI) regions 1, 2 & 17, respectively). This comparison indicates that the error incurred by ignoring the non-elastic response is generally less than 1 cm over the 21st century but can reach magnitudes of up to several 10s of centimetres in low viscosity areas. This error can have large spatial gradients where crustal uplift in ice covered (or previously ice covered) areas changes into subsidence when moving away from the loading centres to areas peripheral to the mass loss. The existence of these large gradients indicates the need for loading models with high spatial resolution to accurately simulate sea-level fingerprints in these regions. We conclude that sea-level projections for Alaska, southwestern Canada and the southern Andes should not be based on elastic Earth models.

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Sea Level Fingerprints in a Region of Complex Earth Structure: The Case of WAIS

Journal of Climate ◽

10.1175/jcli-d-16-0388.1 ◽

2017 ◽

Vol 30 (6) ◽

pp. 1881-1892 ◽

Cited By ~ 22

Author(s):

Carling C. Hay ◽

Harriet C. P. Lau ◽

Natalya Gomez ◽

Jacqueline Austermann ◽

Evelyn Powell ◽

...

Keyword(s):

Sea Level ◽

Large Scale ◽

Near Field ◽

Elastic Response ◽

Earth Model ◽

Sea Level Changes ◽

Viscous Effects ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

The Impact

Abstract Sea level fingerprints associated with rapid melting of the West Antarctic Ice Sheet (WAIS) have generally been computed under the assumption of a purely elastic response of the solid Earth. The authors investigate the impact of viscous effects on these fingerprints by computing gravitationally self-consistent sea level changes that adopt a 3D viscoelastic Earth model in the Antarctic region consistent with available geological and geophysical constraints. In West Antarctica, the model is characterized by a thin (~65 km) elastic lithosphere and sublithospheric viscosities that span three orders of magnitude, reaching values as low as approximately 4 × 1018 Pa s beneath WAIS. Calculations indicate that sea level predictions in the near field of WAIS will depart significantly from elastic fingerprints in as little as a few decades. For example, when viscous effects are included, the peak sea level fall predicted in the vicinity of WAIS during a melt event will increase by about 20% and about 50%, relative to the elastic case, for events of duration 25 and 100 yr, respectively. The results have implications for studies of sea level change due to both ongoing mass loss from WAIS over the next century and future, large-scale collapse of WAIS on centennial-to-millennial time scales.

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