Diatoms are single-celled algae, found in nearly all fresh and saline environments, often in high abundances and species richness. Due to their siliceous skeleton, diatoms have high preservation potential in sediments over geological time-scales. Diatoms are good bioindicators of past and present water quality changes because of their well-documented taxonomy and autecology and fast response (within days) to a range of environmental factors such as salinity, water depth and nutrient availability changes. The application of diatoms in paleoenvironmental studies has a long tradition. Variations in diatom assemblages through sediment sequences can reveal changes in paleo-hydrological conditions with high accuracy and resolution in various environmental settings.
Diatoms are widely used in the reconstruction of shore displacement history, especially in the Nordic countries, in connection with the location of prehistoric settlement sites along former shorelines. The isolation of a basin from the sea will change the salinity and water chemistry, which in turn affects the diatom species composition (shift from brackish to freshwater species). By identifying the different species and the good knowledge of their ecology, we can detect the isolation level within the sedimentary sequence with an accuracy of a few cm.
