Master Thesis defense by Ann-Sofie Zinck
Title: Surface velocity and ice thickness of the Müller ice cap, Axel Heiberg Island
Abstract:
Müller ice cap is situated on Axel Heiberg Island in Arctic Canada. It is characterised by a mountanious region separating the ice cap in the east from the outlet glaciers in the west. Research has taken place on the outlet glaciers of the ice cap since 1959, but only limited research has been conducted on the main ice cap, and no full depth ice cores have ever been drilled. The interesting location of the ice cap facing the Arctic Ocean, the chance of finding ice dating back to the Innuitian Ice Sheet, and the fact that no full depth ice cores have been drilled, makes it an obvious place to do so. In order to achieve a long and undisturbed chronology of the ice core, one needs to find a location for the drilling site, where there is a great ice thickness, low surface velocity and little melt. In this project the aim is to make surface velocity maps of the ice cap and estimate the ice thickness to be able to come up with suggestions of possible drill site areas.
Surface velocities are calculated using feature tracking of optical satellite images from the Landsat satellites in the period of 2004-2019. A median velocity map of all Landsat 8 velocity maps is used as validation in modelling the ice thickness and in the investigation of possible drill site areas.
To estimate the ice thickness various methods are used and are being compared to the ice thickness measured by Operation IceBridge. The first method is an iterative inverse method where the ice sheet model PISM works as a forward model. The model is found to work rather well on the ice cap, with a root mean squared error (RMS) of 138.9 m, but overestimates the ice thickness on the outlet glaciers. The second model uses a simple inversion of the shallow ice approximation. It overestimates the ice thickness in areas with low surface slope, but has a RMS of 131.4 m on the ice cap. The third and and fourth models uses Monte Carlo sampling methods of the shallow ice approximation without and with sliding, respectively. The latter uses an initial ice thickness guess, and the modelled ice thickness was proofed not to differ from that initial guess at all. The RMSs on the ice cap of the two models were found to be 132.1 m and 129.9 m, respectively. Finally, the fifth model uses the PISM setup but with an initial geometry defined by the SIA inversion. The RMS on the ice cap is found to be 135.4 m.
Based on the median Landsat 8 surface velocity map, the modelled ice thicknesses and the surface elevation from the Arctic Digital Elevation Model, a map of suggested drill site areas is made. The site which fulfilled the criteria the most is located at 526629 m easting and 8866463 m northing in UTM zone 15N. In this site the surface velocity is 1.2 m/yr , the surface elevation is 1804 m and the modelled ice thicknesses varies from 535-579 m. The melt in this area is estimated to be less than 20 melt days per year based on the backscatter from Sentinel-1.
Supervisor: Aslak Grinsted
Censor: Nanna B. Karlsson, GEUS
Zoom https://ucph-ku.zoom.us/j/62743028477