The PhD defence and trial lecture are fully digital and streamed using Zoom. The host of the session will moderate the technicalities while the chair of the defence will moderate the disputation.
Trial lecture
Climatic implications of plate tectonics
Conferral summary
Ved subduksjon synker havbunnsplater med vannholdige mineraler kontinuerlig ned i Jordas mantel. Dette kan ha ført til at havnivået har sunket tilsvarende 130 m over de siste 230 mill. år. I avhandlingen er det beregnet hvordan endringer i havbunnstopografien forårsaket av platebevegelser påvirker havnivået, og det er trolig denne prosessen som har hatt den dominerende effekten på det globale havnivået de siste 400 mill. år. I denne perioden har stillehavssiden av planeten i hovedsak vært dekket av tynn havbunnsskorpe, mens Afrika-siden har hatt en stor andel tykke kontinentplater. Dette har sannsynligvis ført til raskere avkjøling av mantelen under Stillehavsplaten.
Main research findings
Popular scientific article about Karlsen’s dissertation:
Plate Tectonic Controls on Geodynamic Processes: Earth’s Deep Water Cycle, Sea Level Change and Planetary Cooling Patterns
The motions of tectonic plates in Earth’s deep past can uncover planetary cycles of water and heat that are important for the evolution of our planet. In this thesis water exchange between Earth’s oceans and deep interior (see figure) was estimated, and there was likely a loss of seawater to the mantle corresponding to ~130 m of sea level drop since ~230 Myr ago.
Maps of ancient ocean basins were reconstructed, extending back 400 Myr, and used to infer variations in seafloor depth. The ocean basin volumes estimated from the reconstructions agree well with the paleo-record of global sea level change. Seafloor reconstructions also tell us about past heat loss from Earth’s interior, and the models suggest that the Pacific side of Earth’s interior has been cooling at a much higher rate than its African counterpart during the last 400 Myr.
This asymmetry was caused by the assembly of nearly all thick and insulating continental landmasses into the Pangea supercontinent on the African hemisphere, leaving the Pacific side to diffuse heat through relatively thin seafloor. These findings contribute to the understanding of how plate tectonics influences both Earth’s surface (e.g. sea level) and deep interior through geologic time.
Photo and other information:
Press photo: Krister Stræte Karlsen, portrait; 650px. Photo: Private
Other photo material: Figure with description and credit as specified in the article above, size 1000px.