PhD defence by Anne Solgaard – Niels Bohr Institute - University of Copenhagen

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PhD defence by Anne Solgaard

Large-scale Modeling of the Greenland Ice Sheet on Long Timescales

Abstract
The stability of the Greenland ice sheet has global implications through sea level. Even smaller reductions in ice-sheet size can raise sea level enough to lead to complications for societies worldwide. In this work, the stability and evolution of the Greenland ice sheet on long timescales is investigated as well as its early history. The studies are performed using an ice-sheet model in combination with relevant forcing from observed and modeled climate. Computationally fast, adaptive forcing patterns were constructed. They take into account that the forcing patterns change in a non-uniform way in response to changes in ice-sheet geometry and climate.  Using these patterns, the temperature threshold of irreversible decay of the ice sheet is found to lay 4-5 K above present levels, but when basal sliding is accounted for in the ice-sheet model it is shifted towards colder temperatures. How much depends on the choice of basal sliding formulation.  The regrowth of the Greenland ice sheet after complete disintegration is found to be inhibited by a Föhn effect which increases temperatures in the interior Greenland.  The early history of the Greenland ice sheet is also studied, and the great variability in ice-sheet geometry in the Pliocene to early Pleistocene is demonstrated.  The effects of a hypothesis about mountain building in Greenland on ice sheet initiation are investigated. According to this, the present-day Greenland topography was formed during 2 phases of uplift since the late Miocene. Our simulated ice sheets are in line with geologic observations, and the uplift enhances the effect of the long-term climatic cooling over the period for ice sheet initiation in Greenland.  Output of temperature and precipitation from the climate model, EC-EARTH, is investigated and a method for inferring Greenland precipitation anomalies from the large-scale circulation-patterns is tested. We find that it describes South Greenland precipitation well despite shortcomings due to mathematical constraints.

Opponenter:

Nina Kirchner
Institutionen för naturgeografi och kvartärgeologi
Bert Bolincentret för klimatforskning
Stockholms universitet

Roderik S. W. van de Wal
Institute for Marine and Atmospheric research Utrecht
Utrecht University

Supervisors
Christine Hvidberg, Associate professor, Centre for Ice and Climate

Gudfinna Adalgeirsdottir, Dr. sc. nat., DMI

Chairman of assessment committee
Bo Vinther, Associate professor, Centre for Ice and Climate

 If interested please contact Anne Solgaard for a copy of the thesis (solgaard@ gfy.ku.dk).