The eruption of the Toba volcano on the island of Sumatra occurred about 74,000 years ago. This eruption, the Younger Toba Tuff (YTT), is currently identified as the largest volcanic event of the Quaternary. It is believed to have released 2,800 km3 of volcanic material into the atmosphere. It left behind the largest caldera of the Quaternary.

However, its global climatic impact is to date very little known and widely debated. This thesis is based on the hypothesis that the eruption of Toba, by modifying the ocean-atmosphere dynamics of the tropical region, had an impact on climate. The objective is then to see if the Toba eruption had an impact on the climatic phenomena of the Indian monsoon and the Indian Ocean Dipole (DOI). For this purpose, four sea cores taken from the Indian Ocean will be studied at very high resolution over a large climatic period in order to reconstruct the variability of the monsoon and the DOI. The surface ocean and thermocline temperatures, which are very sensitive to DOI, will be traced thanks to the Mg/Ca ratio of planktonic foraminifera shells.  

This ratio, combined with the oxygen isotopes of the foraminifera shells, will also allow the reconstruction of salinity variations in the surface ocean. Variations in the intensity of upwellings will be estimated from the foraminiferous assemblages. Finally, the variations of major and minor elements and traces in the sediment will make it possible to reconstruct indicators of precipitation and wind contributions. The comparison of all these parameters will allow the reconstruction of monsoon and DOI variations with an accuracy of about a hundred years and thus highlight the possible influence of Toba. 

Thesis supervisor: Annachiara Bartolini

Paris Paleontology Research Center (CR2P)

Co-supervisor; Eva Moreno

Laboratory of Oceanography and Climate: experiments and numerical approaches (LOCEAN)