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Abstract. Determining the future evolution of the Antarctic IceSheet is critical for understanding and narrowing the large existinguncertainties in century-scale global mean sea-level-rise (SLR) projections.One of the most significant glaciers and ice streams in Antarctica, ThwaitesGlacier, is at risk of destabilization and, if destabilized, has thepotential to be the largest regional-scale contributor of SLR on Earth. Thisis because Thwaites Glacier is vulnerable to the marine ice-sheetinstability as its grounding line is significantly influenced byocean-driven basal melting rates, and its bedrock topography retrogradesinto kilometer-deep troughs. In this study, we investigate how bedrocktopography features influence the grounding line migration beneath ThwaitesGlacier when extreme ocean-driven basal melt rates are applied.Specifically, we design experiments using the Ice-sheet and Sea-level SystemModel (ISSM) to quantify the SLR projection uncertainty due to reportederrors in the current bedrock topography maps that are often used byice-sheet models. We find that spread in model estimates of sea-level-risecontribution from Thwaites Glacier due to the reported bedrock topographyerror could be as large as 21.9 cm after 200 years of extreme ocean warming.Next, we perturb the bedrock topography beneath Thwaites Glacier usingwavelet decomposition techniques to introduce realistic noise (withinerror). We explore the model space with multiple realizations of noise toquantify what spatial and vertical resolutions in bedrock topography arerequired to minimize the uncertainty in our 200-year experiment. We concludethat at least a 2 km spatial and 8 m vertical resolution would independentlyconstrain possible SLR to ±2 cm over 200 years, fulfillingrequirements outlined by the 2017 Decadal Survey for Earth Science. Lastly,we perform an ensemble of simulations to determine in which regions ourmodel of Thwaites Glacier is most sensitive to perturbations in bedrocktopography. Our results suggest that the retreat of the grounding line ismost sensitive to bedrock topography in proximity to the grounding line'sinitial position. Additionally, we find that the location and amplitude ofthe bedrock perturbation is more significant than its sharpness and shape.Overall, these findings inform and benchmark observational requirements forfuture missions that will measure ice-sheet bedrock topography, not only inthe case of Thwaites Glacier but for Antarctica on the continental scale.

Derivation of bedrock topography measurement requirements for the reduction of uncertainty in ice-sheet model projections of Thwaites Glacier