Háskóli Íslands

February 8th at 14:00 - The Aula

Dissertation title: Climatic fingerprint of volcanic eruptions

Opponents:
Dr. Davide Zanchettin, Assistant professor, University of Ca’ Foscari, Venize.
Dr. Jesse Nusbaumer, Research scientist, NASA Goddard Institute, New York.

Advisor: Dr. Árný Erla Sveinbjörnsdóttir, Research Scientist at the Institute of Earth Sciences, University of Iceland

Doctoral committee: Dr. Hans Christian Steen-Larsen, Research Scientist at the Geophysical institute, University of Bergen
Dr. Jesper Sjolte, Research Scientist, at the Department of Geology, University of Lund
Dr. Halldór Björnsson, group leader of atmospheric research, IMO

Chair of Ceremony: Dr. Andri Stefánsson, Vice Head of the Faculty of Earth Sciences at the University of Iceland

Abstract:
Large equatorial volcanic eruptions cause a dynamical climate response that can influence climate and weather on both annual and decadal-to-multi decadal time scales. Interactions between the main components of the climate system, the atmosphere, ocean and sea ice, are considered to be responsible for the strength and duration of this climate response. However, the exact mechanism by which these components interact is still a matter of debate. Furthermore, less is known about the climate response caused by high latitude volcanic eruptions. The aim of this Ph.D. project is to study the atmospheric circulation response that is initiated after both equatorial and high latitude (North Hemisphere) volcanic eruptions and how that response is related to other components of the climate system. To reveal quantitative information regarding the atmospheric circulation response, the four main modes of the North Atlantic climate variability are studied, the Atlantic Ridge (AtR), Scandinavian Blocking (ScB) and the negative and positive phases of the North Atlantic Oscillation (NAO- and NAO+).
In the first part of this Ph.D. study, the analysis of an Earth System Model (MPI-ESM/OM) ensemble reveals a clear increase in the frequency of the AtR in year 2 after an equatorial volcanic eruption linked to equatorial surface cooling in the first years after an eruption. This is detected using eleven equatorial eruptions and two different methodologies. In accord with earlier studies a possible explanation for the volcanic surface cooling is over-estimation of the atmospheric component of MPI-ESM/OM (ECHAM5). It is also suggested that a decrease in the latitudinal surface temperature gradient (less difference between equator and pole) could explain such a natural AtR response to equatorial volcanic eruptions, but further evidence is required to support that. A prolonged NAO+ frequency increase is identified in years 3-5 after equatorial eruptions. It is argued that since the strong (and potentially over-estimated) volcanic surface cooling is dominating the climate signal in the first years after equatorial eruptions, it prevents the formation of NAO+ in the first two years as would otherwise be expected. A clear volcanic response is identified as NAO+ in years 12-14 in both the atmospheric circulation and the sea ice cover. The atmospheric circulation seems to be responding to the sea ice cover reaching a normal, pre-volcanic state in year 12. When compared to the equatorial eruptions, high latitude eruptions leave a weaker significant response in the atmospheric circulation, that might at least partly be due to a smaller number of eruptions analyzed (n=6). However, the results suggest that high latitude volcanic eruptions force the atmospheric circulation into NAO-. Evidence for this is weakly present in year 2 and again (more clearly) in year 10. It is suggested that such a delayed response, seen after both equatorial and high latitude eruptions in this study, might be explained by a shift in the ocean heat transport that is linked to the Atlantic Meridional Overturning Circulation (AMOC).
To link these results to observational data, the second part of the Ph.D. project is dedicated to stable water isotopes in precipitation over the North Atlantic (Global Network of Isotopes in Precipitation, GNIP) and reanalysis (The 20th Century Reanalysis Project V2, 20CRV2). The four main modes of North Atlantic climate variability are identified in the GNIP data although the NAO- and NAO+ patterns are clearer compared to the ScB and AtR. This is used to identify specific stable isotope patterns in the GNIP data after both equatorial and high latitude volcanic eruptions. Together with 20CRV2, the results provide further support of previous findings where AtR and NAO+ is linked to the response in the first four years after equatorial eruptions and ScB and NAO- after high latitude volcanic eruptions.
In the third and last part, stable isotope records in selected Greenland ice cores are in the line of focus where 1-20 years after both equatorial and high latitude volcanic eruptions are analyzed. To support the information retrieved from these records, atmospheric circulation reconstructions spanning the period 1241-1970 CE, are studied in parallel. These results provide further evidence of AtR and NAO+ being associated with equatorial eruptions and ScB and NAO- with high latitude eruptions. This anti-phase is furthermore significantly demonstrated in the reconstructed NAO index analyzed.

About the doctoral candidate:
Hera Guðlaugsdóttir is born in Reykjavik in 1981 and is married to Jón Ragnar Daðason wooden shipbuilder. They live in Breiðabólsstaðir, Álftanes, with their three sons, Ísleifur born 2007, Flóki born 2009 and Þrymur born 2013. Hera's parents are Guðlaugur Kristinn Óttarsson and Valborg Elísabet Kristjánsdóttir. Hera finished her high-school diploma from Fjölbrautaskólinn í Breiðholti árið 2003 and BSc from the Faculty of life and environmental sciences in 2008. After her BSc, Hera worked as a biologist at the Virology department at the University hospital before she began her masters studies in Geology that ended with an MSc in February of 2013. After dwelling in Siglufjörður and building up Breiðabólsstaðir, Hera began work on her Ph.D. project in summer of 2014. Today Hera works at the Iceland's Environmental Agency as a climate specialist.

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