The Overprint of Transient Rheology on Laterally Heterogeneous Viscosity: Influences on Sea‐Level Change Driven by Antarctic Ice Sheet Loss

Abstract

Through bedrock deformation, solid Earth dynamics (specifically, glacial isostatic adjustment or GIA) influences ice sheet mass balance, especially for marine‐based ice sheets like the West Antarctic ice sheet (WAIS). As ice sheets retreat, crustal uplift can help stabilize a marine based ice sheet by reducing the ice exposed at the grounding line. Predicting bedrock deformation requires accurate understanding of rheology. The mantle beneath WAIS is anomalously hot and exhibits low viscosity. In such cases, even on decadal time scales, viscoelastic deformation of the mantle must be considered. GIA studies often consider 3D Maxwell viscoelasticity but transient rheology has been shown to be important on decadal‐centennial timescales. No study has considered the simultaneous modeling of 3D viscoelasticity and transient viscoelasticity. Under several ice sheet histories that span the Last‐Interglacial (122 ky BP) to several hundred years into the future (with a suite of WAIS projections), we show that transient viscoelasticity can have a greater effect than 3D Maxwell viscoelasticity. In particular, in the WAIS region 3D transient viscoelastic uplift rates roughly double 3D Maxwell viscoelastic uplift rates. This has important implications for ice sheet dynamics and to explore the full extent of 3D transient viscoelasticity on such dynamics, a fully coupled system must be considered. While this study focuses primarily on WAIS, we also explore the effects of 3D transient/Maxwell viscoelasticity in the nearfield of the ancient Laurentide ice sheet, which exhibits opposite rheological trends compared with the West Antarctic region due to the relatively cold mantle beneath northern North America.