Magnesium in tests of Neogloboquadrina pachyderma sinistral from high northern and southern latitudes

The intra-species variability of magnesium in calcitic tests of the planktic foraminifer Neogloboquadrina pachyderma sinistral, its relationship to water temperature, salinity and diagenesis, and its potential for paleoceanographic interpretations are investigated. Core-top samples from high northern and southern latitudes and long sediment cores from the Norwegian Sea are investigated for their Recent foraminiferal magnesium content and the variability of magnesium during the past approximately 180,000 years. The quantitative measurement of magnesium was performed by electronmicroprobe analysis. Sample contamination as well as the influence of early diagenetic processes, potentially altering the original element content, can be ruled out for the samples and the time period considered here. Magnesium concentrations in N. pachyderma sinistral are generally lower than published concentrations within other species. Moreover, the foraminiferal tests appear to be undersaturated with respect to magnesium for the water temperatures they have exper i e n c e d . Magnesium concentrations in Recent N. pachyderma sinistral covary most closely with surface water temperature. Salinity changes are of minor importance. Downcore magnesium variations covering the last climatic changes correlate to sedimentological and geochemical parameters. In general, relatively high magnesium concentrations appear during interglacials, whereas low magnesium concentrations occur during glacial periods. Even short climatic events, such as the Younger Dryas cooling, are reflected in the magnesium signal. It is therefore suggested that magnesium in foraminiferal tests reflects relative water temperature variations even at high latitudes, and thus may serve as a paleoceanographic tool to reconstruct changes in surface water circulation.