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ELSEVIER Marine Micropaleontology 25 (1995) 169-I 86 Yi#iln1tnom OLOEY

Summary: ELSEVIER Marine Micropaleontology 25 (1995) 169-I 86
Yi#iln1tnom OLOEY
Benthic foraminiferal distribution and recolonization of formerly
anoxic environments in Dramrnensfjord, southern Norway
E. Alve
Received 4 August 1994;accepted after revision 10January 1995
Investigations of living (stained) benthic foraminifera in the surface (O-l cm) sediments along a depth transect in Dram-
mensfjord, southern Norway, have been carried out on samples collected in 1984 and during all four seasons in 1988. The
transect runs through strongly variable environments from a well oxygenated, brackish surface layer to anoxic waters of slightly
less than normal marine salinity. The objectives were to study foraminiferal recolonization patterns after a prolonged period
( > 5 years) of nearly permanent anoxic bottom water conditions in the lower parts of the transect, the seasonal stability of the
assemblages after recolonization, and interspecific tolerances to various environmental parameters (i.e., temperature, salinity,
dissolved oxygen concentration, water depth). When the redox-boundary was at its shallowest position in the water column
(30-35 m waterdepth; salinity 29-30%0), Ammodiscus? gullmarensis was dominant adjacent to the anoxic areas. This represents
the first record of agglutinated dominated assemblages bordering anoxic environments. It took more than one year after reaeration
before the areas, where anoxic conditions had prevailed for more than five years, became suitable for colonization. By 1988, the
foraminiferal standing crop had more than doubled in areas influenced by the transitional water masses and living (stained)
individuals were present down to the redox-boundary. Additionally, four species, which were not found along the transect in
1984, had been introduced. These immigrants had probably been transported into the area in suspension from the south.


Source: Alve, Elisabeth - Department of Geosciences, Universitetet i Oslo


Collections: Geosciences