The effect of the North-East Greenland Ice Stream (NEGIS) on the Greenland ice sheet in changing climates

• Main Author: Otsu, Shoko
• Format: Other/Unknown Material
• Language: English
• Subjects: 450; Greenland; Weertman; East Greenland; Ice Sheet
• Online Access: http://hdl.handle.net/2115/28752

The North-East Greenland Ice Stream (NEGIS) was discovered as a large fast-flow feature in north-east Greenland by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets), which simulates the large-scale dynamics and thermodynamics of an ice sheet three-dimensionally and over time. In the first part of my study, paleoclimatic simulations are carried out. We simulate the evolution of the ice sheet on a 20-km grid for the period from 250 ka BP until today. Spin-up simulations are from 422 ka BP until 250 ka BP, and the time step for all model components is 5 a. It is driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. In the 20-km resolution runs, we employ two different types of simulations, one is variation of the basal sliding coefficient in the Weertman sliding law for the NEGIS area, and the other is consideration of the effect of surface melt-water to basal sliding at NEGIS. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and optimize the basal sliding law in the NEGIS area by minimizing the misfit between simulated and observed surface elevations and velocities. Tuning the basal sliding coefficient shows a very clear effect on the NEGIS, and by comparison with velocity data, provides a reasonable value of the coefficient. On the other hand, the surface melt-water affects only the ice margin, and therefore cannot explain the onset of the NEGIS as far upstream as observed. In the second step, 10-km resolution simulations are carried out with a modified domain map based on Fahnestock et al. (1993) in order to have a more detailed representation of the NEGIS. The model time is from 127 ka BP until today without spin-up simulations, and the time step for all model components is 1 a. Like for the 20-km simulations, fast sliding in the ...