PhD Defence Danjal Longfors Berg

Principal supervisor:

Professor Shfaqat Abbas Khan, DTU Space

Co-supervisor:

Senior researcher Valentina Roberta Barletta, DTU Space

Examiners:

Associate professor John Peter Merryman Boncori, DTU Space

Senior researcher Peter Henrik Voss, GEUS, Denmark

Senior researcher Halfdan Pascal Kierulf, Norwegian Mapping Authority, Norway

Chairperson at defence:

Senior scientist Henriette Skourup, DTU Space

Summary

The last ice age was at its maximum 21,000 years ago and ended about 11,000 years ago. Though the last ice ended there is still vast amount of ice still present on the Earth in the form of ice sheets for Greenland and Antarctica and glaciers worldwide. Glaciers and ice sheets are currently melting at an alarming rate causing sea level rise. The ice sheets and glaciers hold about 58m of potential sea level rise whereas Greenland is currently contributing to 0.8mm/year.

The solid Earth responds to a change in the mass load from past and present day ice loss and gain. The Earth layer closest to the surface is the lithosphere. The lithosphere responds with an elastic deformation much like a spring that can compress and decompress. The next layer towards the Earth core is the mantle. The mantle responds viscoelastic, like a spring with a delayed dampening effect, whereas the delay is so prolonged that it can take 1000nds of years to return to an equilibrium state. The viscoelastic effect from ice sheets is called Glacial Isostatic Adjustment (GIA).

In Greenland we have over 60 permanent GNSS stations that monitors the land deformation. In this thesis these stations have been used to distinguish between elastic and GIA effects for vertical and horizontal land movement. These measurements help refine global GIA models and track local glacier dynamics. This PhD have resulted in three articles where the first study was for vertical land motion with emphasis on including mass change from peripheral glaciers. The second was about horizontal land motion with emphasis on tectonic plate motion and a general inward contraction GIA field. The last study was a local study for the largest glacier in Greenland, Sermeq Kujalleq (Jakobshavn isbræ) and how the glacier have lost and gained mass for the past decade. The interannual mass change could be observed in the GNSS time series and was correlated with changing ocean temperature.