Benthic foraminiferal distribution and abundance changes in Skagerrak surface sediments: 1937 (Hoglund) and 1992/1993 data compared

Both living (stained) and dead (unstained) foraminiferal assemblages from surface sediments (0-2 cm) in the northwestern part of the Skagerrak have been studied in order to (1) define and characterize the distribution of various modem benthic environments and (2) by comparing these findings with surface samples collected 40-60 years ago, to document possible faunal changes that might have occurred. The investigated area is physiographically divided into the Norwegian slope, the Skagerrak Basin, and the Danish slope. The latter is under the influence of the Jutland Current, while the basin and the investigated parts of the Norwegian slope are bathed in Atlantic water. All areas have bottom waters with a high oxygen concentration. Three living (stained) and three dead (unstained) assemblages occupy the three physiographic areas. Only one assemblage (on the Norwegian slope) is common to both the living and dead assemblages but the boundaries between them lie at comparable depths. The higher standing crops are found on the fertile Danish slope while the lower ones are in the deep basin where the diversity is at a maximum. In the dead assemblages, the relative abundance of agglutinated tests increases with depth. Comparison with data collected 40 to 60 years ago shows increases in absolute numbers of tests, especially in the deep basin. There are changes in assemblage compositions in all areas. The dominant species found in 1937 are different from those of 1992/1993. There is a major change in the basin where one agglutinated species has changed its depth distribution downslope and two present day abundant species are new arrivals. These faunal events are probably linked to environmental changes.