Morphological variation of Emiliania huxleyi and sea surface salinity

Morphometric analysis of coccoliths of various coccolithophore species from core top and culture samples has revealed that the morphology of single placoliths can be affected by environmental parameters such as temperature, salinity, and productivity. In this study, we have tested the morphological variations of placoliths of Emiliania huxleyi, the most common coccolithophore species in the modern ocean, with respect to environmental gradients. We have investigated especially the potential effect of salinity on the morphology, as it is known from culture studies that the growth of E. huxleyi placoliths is strongly influenced by varying salinities. Morphometric analysis of about 2150 placoliths from 37 globally distributed core top and plankton samples revealed that the morphology of E. huxleyi varies significantly along a sea surface salinity gradient from 33 to 38. Morphological parameters such as the mean size of placoliths are used as explaining variables in multiple regression analysis to reconstruct sea surface salinities (SSS). The best model for mean SSS yields an R2 of 0.88 with a standard error of 0.49 whereas statistical models describing surface water temperature or productivity are less reliable and accurate. Application of the best model to plankton samples allows the prediction of in-situ salinities within given error estimates. The application of the best model to fossil assemblages from the LGM, however, is more puzzling. Paleosalinity reconstructions in the South Atlantic, the Caribbean Sea, and the subtropical Atlantic are in good agreement with the published values.