Numerical simulations of the Cordilleran Ice Sheet (CIS) : Implementing a new module to the ice code ARCTIC-TARAH

Abstract: Paleoglaciology is an area of research where numerical reconstruction is actively used to understand the process of ice sheet growth and decay throughout past glacial periods, and numerical simulation of ice dynamics is a tool to reproduce the behaviors of the ice sheet and shelf under given conditions. ARCTIC-TARAH, designed by the Bolin Centre for Climate Research for simulating ice sheet dynamics, is developed based on the Pennsylvania State University Ice sheet model (PSUI). We arrange ARCTIC-TARAH for the simulation of the Cordilleran Ice Sheet (CIS), which periodically appears in the northwestern corner over North America during glacial periods, and simulate for 30,000 years in order for the researchers at the Bolin Centre to be able to perform real CIS paleo-simulations in the future. Based on the Last Glacial Maximum (LGM), the Mid-Holocene (MH), and the presenttime (PT) climate data, several different experiments are run for arbitrary 10,000-30,000 years. We discuss the potential problems of the CIS simulation and suggest further improvements on the model. The major issues encountered are (1) the basal topography, (2) grounding line treatments, and (3) the climate setting. Both the steep and jagged surface of a mountain range and the basal topography near the edge of a continental slope require close attention for numerical stability. Because the topography in some areas of the coastline is very steep and the width ofthe continental slope is narrow, there is a large amount of ice mass that flows out into the ocean from land. The transition zone between the ice sheet and shelf may approach the continental slope in a relatively short time. This large volume flux across the grounding line on the steep seabed overwhelms the stability of the model. In addition, the model uses a PDD (positive-degree-day) method to approximate the budget of ice accumulation and ablation. We suggest either implementing a better PDD method or coupling it with a climate model to capture the coastal and continental climate characteristics, as well as the local extreme climate in the mountains and along the coast.