Diatom analyses of lake sediments from Tristan da Cunha, South Atlantic, and inferred climate changes
Diatoms are microscopic siliceous algae that can be used as environmental indicators and are very useful in reconstructing past environment and climate changes. Species composition and changes in production of algae can tell us about changes in pH, nutrients, light conditions, temperature etc in the lake. In this project we are studying diatoms in lakes on Tristan da Cunha. Tristan da Cunha is a remote, volcanic archipelago in the central South Atlantic Ocean. During expeditions to the island group in 2003 and 2010, lake sediment cores were collected, brought back to Lund University, and are now being analyzed.
We are interested in climate linkages and feed back mechanisms between then Southern and Northern hemisphere. The Tristan da Cunha archipelago is situated at the northern limit of the Southern Hemisphere Westerly winds. This wind belt has a considerable impact on ocean circulation and may play a critical role in global climate variability. In general there is a need for more climate data from the Southern hemisphere to understand climate variability both on a regional and hemispheric scale.
In our study the diatom data is used in combination with geochemical and pollen analyses. Altogether, the data suggest recurring periods of high precipitation on Tristan da Cunha during the past c. 11 000 yrs. Our hypothesis is that these precipitation phases are coupled to changes in the strength and position of the westerly winds.