Abstract
Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. 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 Sixth 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 parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, 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 result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.
| Original language | English |
|---|---|
| Pages (from-to) | 985-1008 |
| Number of pages | 24 |
| Journal | Cryosphere |
| Volume | 14 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 16 Mar 2020 |
Funding
Acknowledgements. We thank Surui Xie, Neil Fraser and an anonymous reviewer for their constructive comments. Donald Slater and Fiamma Straneo were supported by NSF grant nos. 1916566 and 1756272 and by NASA grant no. NNX17AI03G. Denis Felikson’s research was supported by an appointment to the NASA Postdoctoral Program at the NASA Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASA. Chris Little acknowledges financial support from NSF grant no. 1513396. Heiko Goelzer has received funding from the programme of the Netherlands Earth System Science Centre (NESSC), financially supported by the Dutch Ministry of Education, Culture and Science (OCW) under grant no. 024.002.001. Mathieu Morlighem was supported by the National Science Foundation’s ARCSS program (no. 1504230). Sophie Nowicki was supported by the NASA Sea Level Change Team and Cryosphere Sciences Programs. Computational resources for performing MAR future projections have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.–FNRS) under grant no. 2.5020.11 and the Tier-1 supercomputer (Zenobe) of the Fédéra-tion Wallonie Bruxelles infrastructure funded by the Walloon Region under the grant no. 1117545. Thanks to Brice Noël for RACMO2.3p2 output, to Ellyn Enderlin and Michalea King for ice flux datasets, and to Jeremie Mouginot for sharing ice sheet basin delineations. All members of the ISMIP6 collaboration are thanked for discussions and feedback, notably at ISMIP6 meetings, with particular thanks to Hélène Seroussi, Alice Barthel and Tim Bartholomaus. We thank the Climate and Cryosphere (CliC) effort, which provided support for ISMIP6 through sponsoring of workshops, hosting the ISMIP6 website and wiki, and promoting IS-MIP6. We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP5 and CMIP6. We thank the climate modelling groups for producing and making available their model output, the Earth System Grid Federation (ESGF) for archiving the CMIP data and providing access, the University at Buffalo for IS-MIP6 data distribution and upload, and the multiple funding agencies who support CMIP5, CMIP6 and ESGF. This is ISMIP6 publication no. 6. Financial support. This research has been supported by the Na- tional Science Foundation, Office of Polar Programs (grant no. 1916566), the National Science Foundation, Division of Ocean Sciences (grant no. 1756272), the National Aeronautics and Space Administration (grant no. NNX17AI03G), the National Science Foundation, Office of Polar Programs (grant nos. 1513396 and 1504230), the Netherlands Earth System Science Centre (grant no. 024.002.001), the Fonds De La Recherche Scientifique – FNRS (grant no. 2.5020.11), and the Fédération Wallonie-Bruxelles (grant no. 1117545).
