Changes in distribution of calcareous benthic foraminifera in the central Barents Sea between the periods 1965-1992 and 2005-2006

摘要

Live benthic foraminifera assemblages from 30 surface sediment samples taken in 2005 and 2006 from the central Barents Sea are compared with total benthic foraminifera assemblages from a database containing samples taken between 1965 and 1992. We evaluate the hypothesis that observed environmental changes in the region have led to observable shifts in benthic foraminiferal fauna. Of the 12 infaunal calcareous species studied marked decreases were observed in cold water species Buccella spp., Elphidium excavatum, Islandiella norcrossi and Nonionellina labradorica. A decline combined with a marked change in spatial distribution is seen in Cassidulina laevigata, Trifarina fluens, Stainforthia loeblichi, Cassidulina reniforme, Cassidulina neoteretis, Melonis barleeanus, and Pullenia bulloides. Warm water species Epistominella nipponica is the only species of these 12 that increased in abundance. The general shift toward dominance of warm water species and temperature tolerant species agrees well with the observed temperature increase in the basin. At the level of individual data points, a relationship between assemblage change and environmental change is not straightforward. The comparison of the new data with the database also displays a shift toward higher abundances of more fragile species, which can be attributed to method differences. The species that display the most pronounced change are those associated with cold water and proximity of the ice edge. The magnitude of benthic foraminiferal change in the study area is largest in a conspicuous belt that appears to follow roughly the Polar Front. This area has a lower temperature and salinity gradient through the last decades than the rest of the study area, and its high faunal change may be due to the position of the Polar Front moving away from this area, and associated changes in the sea ice edge.