MCINTOSH

At least two potential climate tipping points involving ice sheet-ocean interactions have been identified, one involving warm ocean waters reaching ice-shelf cavities and the other related to ice-sheet instabilities triggered by increased ocean melting. The MCINTOSH project, together with collaborators at the US Department of Energy (DOE) aims to develop and couple ice-sheet, ocean and sea-ice climate-model components required to investigate these phenomena. In collaboration with the Climate, Ocean and Sea-Ice Modeling (COSIM) group at Los Alamos National Laboratory (LANL), the MCINTOSH project is undertaking several development tasks in the Model for Prediction Across Scales (MPAS) Ocean and the Accelerated Climate Model for Energy (ACME). The proposed model development includes 1) implementation of ice-ocean boundary conditions in the coupler, 2) addition of a wetting-and-drying scheme to MPAS Ocean to enable moving horizontal boundaries, 3) improvements in the pressure-gradient calculation (needed when the ice-ocean interface is steep, as at ice-shelf calving fronts), 4) improvements in the sub-grid-scale representation of heat and salt transport below ice shelves and 5) support of ocean top cells, analogous to the bottom cells used to represent the bathymetry. While a primary motivation of the MCINTOSH project is to develop a general-purpose tool for studying coupled ice sheet-ocean interactions on a continental scale, the project will include a set of at least four century-long projections with the coupled ocean-land ice-sea-ice system with atmospheric forcing from CIMP5 simulations under two future climate scenarios: “business-as-usual” emissions (RCP 8.5 scenario) and a control climate (repeating forcing from the decade 2000-2010). Our results will be directly comparable to previous, lower-resolution work with static ice-sheet geometry. The projection results will be used to address the following three science questions: 1. Under what circumstances (if any) do our simulations show the deterioration of slope fronts in the ocean, allowing warm water to flow under ice shelves? 2. Do our projections show that increased melting can trigger irreversible ice-sheet retreat? 3. What range and rates of sea-level change from ice-sheet mass loss are seen in our projections?