21st century ocean forcing of the Greenland Ice Sheet for modeling of sea level contribution

Abstract

Abstract. Changes in the ocean are expected to be an important determinant of the Greenland Ice Sheet's future sea level contribution. Yet representing these changes in continental-scale ice sheet models remains challenging due to the small scale of the key physics, and limitations in processing understanding. Here we present the ocean forcing strategy for Greenland Ice Sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change 6th Assessment Report. Beginning from global atmosphere-ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland Ice Sheet models, termed the retreat and submarine melt implementations. The retreat implementation parameterizes glacier retreat as a function of projected submarine melting, is designed to be implementable by all ice sheet models, and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat, and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly-constrained parameterisations and as such, further research on submarine melting, calving and fjord-shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland Ice Sheet models to be systematically and consistently forced by the ocean for the first time, and should therefore result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM

“…Result in the retreat is up to 15 km by 2100 in RCP8.5-Rmed scenario (Slater et al, 2019a). The retreat mask for RCP8.5-Rhigh in 2100 is exemplary shown in Fig.…”

“…Therefore, we aim to briefly outline the external forcing approach. Further details are given inGoelzer et al (2020),Nowicki et al (2020a,Slater et al (2019a) andSlater et al (2019b).…”

Estimating Greenland tidewater glacier retreat driven by submarine melting

“…Terminus positions are taken from a number of published sources (Fig. 2, Table S1 in the Supplement, Andresen et al, 2012;Steiger et al, 2018;Lea et al, 2014;Haubner et al, 2018;Catania et al, 2018;Cowton et al, 2018;Moon and Joughin, 2008;Joughin et al, 2018;Bunce et al, 2018;Carr et al, 2017). Broadly, these records can be organized into long records from a handful of individual glaciers and shorter satellite-era records from almost all of the fastest-flowing tidewater glaciers in Greenland ( Fig.…”

Glacier Forecast: Jakobshavn Isbrae Primed for Thinning and Acceleration

“…At present, the Greenland Ice-Sheet has 7.4 m of sea-level rise potential (Aschwanden et al, 2019;Morlighem et al, 2017). Projections of ice loss from Greenland during the 21 st Century (Goelzer et al, 2020) rely on simpli ed, glacier-dependent relationships between the ocean and the outlet glaciers that drain the ice sheet (Slater et al, 2019a;2019b). Yet it will take years, perhaps decades, to determine whether such simple assumptions will hold true in the future.…”