Spatial probabilistic calibration of a high-resolution Amundsen Sea Embayment ice-sheet model with satellite altimeter data

• Main Authors: Wernecke, Andreas, Edwards, Tamsin L., Nias, Isabel J., Holden, Philip B., Edwards, Neil R.
• Format: Text
• Language: English
• Published: 2019
• Subjects: Amundsen Sea; Antarctic; Pine Island Glacier; The Antarctic; Antarc*; Antarctica; Ice Sheet; Pine Island; Smith Glacier
• Online Access: https://doi.org/10.5194/tc-2019-156; https://www.the-cryosphere-discuss.net/tc-2019-156/

Probabilistic predictions of the sea level contribution from Antarctica often have large uncertainty intervals. Calibration with observations can reduce uncertainties and improve confidence in projections, particularly if this exploits as much of the available information as possible (such as spatial characteristics), but the necessary statistical treatment is often challenging and can be computationally prohibitive. Ice sheet models with sufficient spatial resolution to resolve grounding line evolution are also computationally expensive. Here we address these challenges by adopting a novel dimension-reduced approach to calibration combined with statistical emulation of the adaptive mesh model BISICLES. We find the most likely contribution to global mean sea level rise from the Amundsen Sea Embayment (ASE) over the next 50 years is 10.4 [0.6, 23.3] mm (mode and 5–95 % probability interval), a substantial reduction in uncertainty from the uncalibrated estimates of 9.6 [−5.9, 78.2] mm. We predict retreat of the grounding line along most parts of the ASE coast with high confidence, with a maximum inland extent of around 28 km at Smith Glacier. The model behaviour is much more consistent with observations if, instead of Bedmap2, a modified bedrock topography is used that most notably removes a topographic rise near the initial grounding line of Pine Island Glacier, though this does influence the future mass loss less than basal traction and viscosity scaling parameters. The ASE dominates the current Antarctic sea level contribution, but other regions have the potential to become more important on centennial scales. These larger spatial and temporal scales would benefit even more from methods of fast but exhaustive model calibration. Our approach therefore has the potential to improve projections for the Antarctic ice sheet on continental and centennial scales by efficiently improving our understanding of model behaviour, and substantiating and reducing projection uncertainties.