The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway

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Surface sediment samples taken by box corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous species Cribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data.Trifarina angulosa and, to a lesser extent, Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, the Melonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized by Cassidulina teretis and Pullenia bulloides. Below 1400 m, three foraminiferal assemblages are found: C. subglobosum is found from 1400 to 2000 m, Cibicidoides wuellerstorfi and Epistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m, Oridorsalis umbonatus and Triloculina frigida dominate the fauna.All of the Elphidium excavatum tests found in this study and the Cassidulina reniforme tests found above 500 m water depth were found to be reworked.Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance of C. wuellerstorfi and E. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies of O. umbonatus and T. frigida coincide with low organic carbon content. We suggest that C. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereas O. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters.

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Mackensen, A. , Sejrup, H. P. and Jansen, E. (1985): The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway , Marine micropaleontology, 9 , pp. 275-306 .

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