8th International Nannoplankton Association Conference


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Karin A. F. Zonneveld:
delta18O of Thoracosphaera heimii from cultures and S Atlantic surface sediments in relation to temperature and salinity gradients

The delta18Ocalcite composition of foraminifera, and more recently pteropod, shells is widely used to reconstruct past sea-surface temperatures and salinities. Unfortunately, physiological effects, such as photosynthesis of algal symbionts, as well as migration within the water-column, dissolution and size-related changes in growth rate and calcification, may influence the degree in which foraminiferal calcite produces an oxygen isotopic equilibrium with sea-water. The use delta18Ocalcite composition of pteropod shells is restricted due to their dial vertical migration and the rapid dissolution of their shells.

Some of these problems might be overcome by using the delta18Ocalcite composition of primary producers with a habitat at a relatively fixed water-depth, producing shells with a high preservation potential. Thoracosphaera heimii seems to fulfil these requirements. Recent studies on its distribution in the upper part of the water-column suggest a relatively fixed habitat at the upper part of the thermocline. Furthermore, its shells are widely abundant in surface sediments of the world's seas and oceans and they can be found at depths well below the lysocline.

In this paper, information will be provided on the delta18Ocalcite composition of T. heimii shells cultured under various temperature and salinity conditions. Furthermore, a comparison will be made between the stable oxygen isotopic composition of T. heimii shells from S Atlantic surface-sediment samples with temperature and salinity data from the upper water-column. The potential use of delta18Ocalcite composition of T. heimii to reconstruct past temperature and salinity will be discussed.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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