Estuarine foraminiferal distribution in Sandebukta, a branch of the Oslo Fjord

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Abstract
Sandebukta is an inlet branching out from the main body of the Oslo Fjord, through which it is connected with the Skagerrak and North Sea. The waters of the inlet are of stratified estuarine character, having a main inflow of river water and an intertidal mudflat in the inner part. Bottom surface sediment samples have been analyzed from 64 stations, from the mudflat down to 70 m water depth. Agglutinating foraminifera are represented by 37 species and dominate the benthic assemblage of the inlet, forming 90-100% of the community at most stations. The subordinate calcareous group contains 23 species. The presence of organic test linings is a product of the dissolution of calcareous tests, particularly in shallower waters, where pH is reduced (7.0 on average). A Q-mode factor analysis differentiates six species assemblages. On the western side of the inlet the assemblages form a well developed depth succession related to the estuarine stratification of the water. On the eastern side the distribution of assemblages is modified and partially limited by an increased influx of organic matter originating from industrial pollution. Toward the head of the inlet, depression of the assemblage boundaries and reduced diversities reflect the main inflow of river water.