Reconstruction of past changes in ocean salinity - a compound specific stable hydrogen isotope approach

Abstract

The extent of the general warming related to increasing anthropogenic CO2 emission and its implications for the global climate system are currently under heavy debate. In particular the extrapolation of long term climatic trends relies on complex climate models for the interaction between the atmosphere, the oceans and the land surface. In turn these models require validation based on continuous time series of observational data. However, instrumental based data records only extend as far back as approximately 150 years and thus make the validation of long-term modelling experiments difficult. To obtain information on past climate beyond the instrumental period, so-called paleoceanographic proxies are used. Two of the most targeted paleoceanographic parameters are the sea surface temperature (SST) and sea surface salinity, which determine water density. While past ocean temperatures can be reconstructed relatively accurately from various independent methods, the accurate reconstruction of past ocean salinity has proven to be more difficult. A promising new method for the reconstruction of past ocean salinity has been suggested to come from the hydrogen isotope composition of long chain alkenones (δDalkenone) derived from marine haptophyte algae. Culture studies have shown a strong correlation between hydrogen isotope fractionation and salinity, with decreasing fractionation with increasing salinity. In order to test the applicability of the δDalkenone as a salinity proxy, this thesis presents studies on sedimentary records obtained from various open ocean settings including the greater Agulhas System south of the African continent, the Eastern Tropical Atlantic and the Atlantic sector of the Southern Ocean, as well as coastal ocean margin settings in the Mozambique Channel and offshore Southeast Australia.