MAIN FEATURES OF FORAMINIFERAL DISTRIBUTION REFLECTING ESTUARINE HYDROGRAPHY IN OSLO FJORD

Foraminiferal assemblages have been analysed in sediment surface samples located along three profiles covering the depth interval 1-120 m in Breidangen, a wide basin forming the middle portion of Oslo Fjord. The study concentrates on the distribution of major faunal features, including suborders and diversities (number of species, Shannon-Wiener index, equitability). In addition, species distribution is recorded and Q-mode factor analysis has distinguished six assemblages. Measurements of hydrographical properties (temperature, salinity, dissolved oxygen) reveal the estuarine stratification of the water column, which is reflected also by the faunal parameters. On the basis of these features, the following subdivision is proposed (with increasing depth):. (1) Seasonal layer dominated by calcareous species in the upper, and agglutinated species in the lower part, with low to intermediate diversities; (2) Transitional layer characterized by a maximum in diversity and a reduction in the agglutinated component; (3) Stable deeper water showing high diversity and a further decrease in the agglutinated component. The generally higher frequency of calcareous foraminifera below the seasonal water layer on the eastern side of Breidangen compared to the western side is mainly attributed to the influence of inflowing Skagerrak water. Additionally, it may be a result of increased supply of organic matter to the western side, increasing the oxygen demand in this area. © 1990 Elsevier Science Publishers B.V.