Jordvarme gir raske isbevegelser på Grønland. Silje Smith-Johnsen disputerer 15.november 2019 for ph.d.-graden ved Universitetet i Bergen

Isstrømmer (blå) frakter is fra toppen av Grønland mot havet. Ill.: NASA/Goddard Space Flight Center Scientific Visualization Studio

Jordvarme gir raske isbevegelser på Grønland

Silje Smith-Johnsen disputerer 15.november 2019 for ph.d.-graden ved Universitetet i Bergen med avhandlingen “Dynamics of the Northeast Greenland Ice Stream: the role of geothermal heat and subglacial hydrology”.

Silje Smith-Johnsen
Silje Smith-Johnsen har studert isstrømmer på Grønland. Foto: Eva Bjørseth

I sin avhandling viser Silje Smith-Johnsen at de raske isbevegelsene nordøst på Grønland kan forklares med uvanlig høy jordvarme under innlandsisen.

Områder av innlandsisen som beveger seg mye raskere enn den omkringliggende isen blir kalt isstrømmer. Smith-Johnsen viser at isstrømmen på Nordøst Grønland kan ha oppstått som følge av økt jordvarme.

Jordvarme er en naturlig varmefluks fra jordens indre og kan føre til at bunnen av innlandsisen når smeltepunktet. Når dette skjer, får vi smeltevann under høyt trykk mellom isen og berggrunnen. Dette fungerer som smøring under isen og kan forklare hvorfor isstrømmen beveger seg så raskt mot havet.

Smith-Johnsen har tatt del i feltarbeid på innlandsisen for å måle hastigheten til isstrømmen, samt de fysiske egenskapene til jordskorpen under isen.

Jordvarme er vanskelig å måle direkte, men ved hjelp av numeriske modeller har Smith-Johnsen beregnet hvor høy jordvarme som skal til for å oppnå de observerte ishastighetene på Nordøst Grønland. Ved å ta hensyn til smøreeffekten fra smeltevannet, viser hennes arbeid at isbevegelsene er svært sensitiv til jordvarmen.

Smith-Johnsens arbeid bidrar til å øke forståelsen av de komplekse isbevegelsene på Grønland, og forbedre representasjonen av isstrømmer i numeriske modeller. Resultatene er kritiske i arbeidet med å forbedre prognosene for Grønlandsisens bidrag til økt havnivå i ett fremtidig varmere klima.

Tid og sted for disputas

15. november 2019 kl. 13.15 i Auditorium 5, Realfagsbygget.

Personalia

Silje Smith-Johnsen (f.1990) er fra Bergen og har mastergrad fra Institutt for Geovitenskap, UiB og Universitetsenteret på Svalbard.

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