Variations of the Antarctic Ice Sheet in a Coupled Ice Sheet‐Earth‐Sea Level Model: Sensitivity to Viscoelastic Earth Properties

Abstract

A coupled ice sheet‐solid Earth‐sea level model is applied to long‐term variations of the Antarctic ice sheet. A set of radially varying viscoelastic profiles in the global Earth model is used to explore feedbacks on ice sheet variability, including one with a very weak upper mantle zone and thin lithosphere representative of West Antarctic regions. Simulations are performed for (1) the deglacial retreat over the last ~20,000 years, (2) the future 5,000 years with greenhouse‐gas scenario Representative Concentration Pathway 8.5 (RCP8.5), and (3) the warm Pliocene ~3 Ma. For the deglacial period a large ensemble of 625 simulations is analyzed, with a score computed for each run based on comparisons to geologic and modern data. For each of the five Earth profiles, the top‐scoring combinations of the other model parameters in the ensemble are used to perform future and Pliocene simulations. For the last deglacial retreat, the viscoelastic Earth profiles produce relatively small differences in overall ice volume and equivalent sea level. In contrast, profiles with weak upper mantle and thin lithosphere produce strong negative feedback and less ice retreat in the future and Pliocene runs. This is due to the faster pace of ice sheet retreat in these runs, leading to greater lags in the viscous bedrock rebound behind the unloading, which allows for greater influence of the viscosity profiles. However, the differences in grounding‐line retreat are located primarily in East Antarctic basins, where a weak upper mantle and thin lithosphere may not be realistic, emphasizing the need for lateral heterogeneity in the Earth model.

An Overview of Interactions and Feedbacks Between Ice Sheets and the Earth System

“…Differences show the impact of a unanimously thin lithosphere and low viscosity mantle (LVZ) versus a standard solid Earth profile (HV). In particular, the LVZ profile results in less ice sheet mass loss (b–d) as a result of a stronger negative feedback between ice sheet mass and solid Earth changes (Pollard et al, ).…”

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

“…Furthermore, models that consider the coupled evolution of the ice sheet-solid Earth system (see Sect. 3.1) will be highly sensitive to the underlying viscosity field (Gomez et al, 2015b;Konrad et al, 2015;Pollard et al, 2017).…”

“…3.1, as has 3D GIA modelling (Sect. 3.2), but since the impact of GIA on ice dynamics has been shown to be strongest in locations where mantle viscosity is unusually low (Pollard et al, 2017) it will be crucial to incorporate lateral variations in Earth structure into future coupled ice sheet-GIA models in 745 order to accurately predict the evolution of the many ice sheets that are located above low viscosity regions (e.g. West Antarctica, Patagonia, Alaska, Iceland; see Sect.…”

Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years

“…These studies use different numerical ice sheet models, and they differ in their approach to climate forcing, ice sheet basal conditions, and ice shelf dynamics, but all represent an attempt to reconstruct the history of the WAIS since the LGM. This is not to say that all modelling attempts reproduce grounding line retreat behind present; the ensemble analysis of Briggs et al () does not appear to predict Late Holocene readvance in the wider WS sector, while in the studies of Pollard et al () and Kingslake et al () model scenarios that involve faster rates of rebound predict slower rates of ice loss and no retreat behind present. This is due to the damping effect of the rapid rebound.…”

“…Upper mantle viscosity across Antarctica is thought to vary by >3 orders of magnitude (Hay et al, 2017;van der Wal et al, 2015;Whitehouse et al, 2019). The associated range in mantle relaxation times significantly perturbs the strength of the feedback between isostatic deformation and ice dynamics in different regions of Antarctica (Gomez et al, 2015;Konrad et al, 2015;Pollard et al, 2017) and motivates the need for a coupled ice sheet-GIA model that incorporates 3-D Earth structure. Gomez et al (2018) use such a model to quantify the effect of incorporating 3-D variations in mantle viscosity compared with a more common 1-D radial profile of mantle viscosity.…”