DOWNCORE DISTRIBUTION OF LIVING CALCAREOUS FORAMINIFERA AND STABLE ISOTOPES IN THE WESTERN BARENTS SEA

Abstract

The density and vertical distribution of living calcareous foraminifera have been studied in six box cores from the shelf depressions in the Western Barents Sea in relation to total organic carbon content and flux to the seafloor, primary production, sedimentation rates, bottom-water masses and stable isotopes. It appears that at least several infaunal species—like Melonis barleeanus , Islandiella norcrossi and perhaps Nonionellina labradorica , Cribroelphidium excavatum clavatum and Cassidulina reniforme —might penetrate down to 8–10 cm below the sediment surface searching for a favorable microhabitat. A deep penetration of some living specimens, notably epifaunal Cibicides lobatulus , into the sediment might result from bioturbation and survival inside polychaete tubes. The highest foraminiferal abundances (up to 130–240 sp/50 cm3) of the six cores were found in the most productive areas on the West Spitsbergen shelf and in the mouth of the Isfjorden (Svalbard) and likely resulted from fast sedimentation and mass accumulation rates of marine organic matter. These factors seemed to be responsible for deeper penetration and habitat depth of the above-mentioned species on the shelf as compared to the northern Barents Sea continental slope. However, the abundance of living calcareous foraminifera on the slope was much higher than in our study, probably due to a greater flux of particulate organic matter produced during the seasonal phytoplankton bloom along the ice-edge margin. In general, more depleted δ18O values (of unstained foraminifera) are found in the box cores obtained beneath pure Atlantic water compared to those beneath cooler bottom water. Estimated δ18O disequilibrium effects for Nonionellina labradorica (0.28‰), Cibicides lobatulus (−0.76‰) and Melonis barleeanus (−0.41‰) support previous findings for these species.