Modelling the evolution of Jakobshavn Isbræ, West Greenland, from 2009 to 2017

Abstract

The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and has been losing mass at an increasing rate since the 1990s, with the greatest losses coming from marine-terminating sectors of the ice sheet where outlet glaciers discharge icebergs into the ocean. Jakobshavn Isbræ drains 7% of the ice sheet area and is one of the fastest flowing outlet glaciers. It has dramatically thinned, retreated and accelerated since the late 1990s. Since 2016 it has modestly slowed, readvanced and thickened, suggesting that it responds rapidly to changes in the water temperature in Ilulissat Icefjord. The complexity of its dynamical behaviour therefore makes it difficult to project its future evolution.

This thesis takes a new approach to modelling Jakobshavn Isbræ, by running hindcast model experiments of the period 2009 to 2017 (inclusive) and assimilating all available data into the model. An iceberg calving rate was derived from satellite observations of velocity and terminus extent, and a method to drive a model of the glacier by the calving rate using the BISICLES ice sheet model was developed. A time-dependent inverse method was applied to assimilate observations into the model and different optimisation methods were considered. The calculated calving rate and optimised input fields were applied to drive hindcast model simulations.

These experiments demonstrate that it is possible to model the evolution of Jakobshavn Isbræ by the regular assimilation of observations into the model. The model was dependent on regular assimilation, raising challenges for future projections of Jakobshavn Isbræ. The applicability of the model to future projections is discussed in this work. A linear viscous sliding law is poorly suited to modelling the future evolution of Jakobshavn Isbræ. ith additional parameter tuning, a regularised Coulomb sliding law may be more appropriate for future projections of the evolution of Jakobshavn Isbræ.

Date of Award	28 Sept 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	A J Payne (Supervisor) & Dann M Mitchell (Supervisor)