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Disputation: Ella Wulfsberg Stokke

Doctoral candidate Ella Wulfsberg Stokke at the Department of Geosciences, Faculty of Mathematics and Natural Sciences, is defending the thesis Linking climatic changes and North Atlantic volcanism across the Paleocene-Eocene Thermal Maximum at Fur, Denmark for the degree of Philosophiae Doctor.

Ella Wulfsberg Stokke. Photo: Private

Ella Wulfsberg Stokke. Photo: Private

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.

Ex auditorio questions: the chair of the defence will invite the audience to ask ex auditorio questions either written or oral. This can be requested by clicking 'Participants -> Raise hand'. 

Trial lecture

Causes and consequences of climate variability: Lessons from the past for understanding present and future climate

Conferral summary (in Norwegian)

Avhandlingen viser hvordan en global oppvarming for ca. 55,9 millioner år siden førte til store klima- og miljømessige endringer i Nordsjøen, trolig påvirket av vulkanske gasser fra den Nord-Atlantiske Vulkanprovinsen. Havoverflatetemperaturen økte mer enn 10 °C, nedbørsmengden økte, og havbunnen ble så oksygenfattig at alt liv forsvant. Både før og etter den globale oppvarmingen sank temperaturene uvanlig mye i Nordsjøen, muligens forårsaket av vulkanutbrudd som spredde hundrevis av vulkanske askelag og store mengder svovel utover Nord-Europa. Avhandlingen viser at den uvanlige størrelsen og eksplosiviteten til vulkanutbruddene ble forårsaket av at store mengder magma kom i kontakt med vann under åpningen av det Nord-Atlantiske havet.

Main research findings

Popular scientific article about Stokke’s dissertation:

Linking climatic changes and North Atlantic volcanism across the Paleocene-Eocene Thermal Maximum at Fur, Denmark

This thesis focuses on Danish sediments deposited in the eastern North Sea basin between 56-54.6 million years ago, including an extreme global warming event called the Paleocene-Eocene Thermal Maximum (PETM) that was triggered by large emissions of carbon to the ocean and atmosphere. We find evidence that sea surface temperatures increased >10 °C across the PETM onset. This warming was accompanied by an intensified hydrological cycle, enhanced erosion of the surrounding landmass, an increase in the production and burial of organic matter, and a decrease in bottom-water oxygen content. Hundreds of ash layers from the North Atlantic Igneous Province (NAIP) are preserved in the Danish sediments. These are the largest explosive basaltic eruptions known, yet their formation is poorly understood. 

The doctoral study find that these ashes were formed due to violent magma-water interactions in a shallow-marine (<200 m) environment during the opening of the North East Atlantic Ocean. The sea surface temperature proxy shows cool periods corresponding to spells of abundant ash deposition from the NAIP. We find that these eruptions could have emitted enough sulfur to have a significant climatic impact, and propose that the NAIP activity may have had a regional cooling effect particularly in the period immediately following the PETM.

Bildet kan inneholde: skråningen, geologi, stein, reise, verden.
Figure: To the left: Palaeogeographic reconstruction from 56 million years ago showing the known extent of the North Atlantic Igneous Province. The red areas show the extrusive NAIP volcanism, and known extent of the sill intrusions are indicated by the dark grey area. Blue areas indicate the ocean, with ocean basins in dark blue. The small map shows the location of the study area Fur within Denmark. To the right: A picture from the fieldwork conducted at the main locality the Stolleklint beach on the northern shore of the island of Fur. Figure/illustration: Stokke, Jones et al. 2019.

Photo and other information:

Press photo: Ella Wulfsberg Stokke, portrait; 500px. Photo: Private

Other photo material: Figure with description and credits as specified in the article above, size 1000px.

Published Jan. 15, 2021 10:00 AM - Last modified Oct. 4, 2021 1:14 PM