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Free keywords:
Arctic, Spitsbergen, benthic foraminifera, oxygen and carbon stable isotopes, paleotemperature, fjords
DDC:
550 - Earth sciences
Abstract:
Modern hydrology of a typical Arctic fjord (Hornsund, SW Spitsbergen, Svalbard) was investigated and compared with commonly used in paleoceanography proxies: benthic foraminiferal assemblages and their stable isotope (Δ18O and Δ13C) composition. The benthic foraminifera from Hornsund comprised 45 species and 28 genera. Their spatial variations follow the zonation pattern, resulting from the influence of Atlantic water at the fjord mouth and glacial meltwaters at the fjord head. At the mouth of the fjord, the total number of species and the contribution of agglutinating species were the highest. In the inner part of fjord, the foraminiferal faunas were poor in species and individuals, and agglutinating species were absent. "Living" (stained) foraminifera were found to be common throughout the short sediment cores (~10 cm long) studied. The stable isotope values of Δ18O and Δ13C were measured on tests of four species: Elphidium excavatum forma clavata, Cassidulina reniforme, Nonionellina labradorica and Cibicides lobatulus. The results confirmed the importance of species-specific vital effects, particularly in the case of C. lobatulus. The variability in the isotopic composition measured on different individuals within a single sample are comparable to isotopic composition of the same species test between sampling stations. The temperatures and bottom water salinities calculated from Δ18O values in different foraminifera tests mirrored those recorded for bottom waters in the central and outer fjords relatively well. However, in the case of the inner fjord, where winter-cooled bottom waters were present, the calculated values from Δ18O were systematically higher by about 2°C. The obtained results imply that particular caution must be taken in interpretation of fjord benthic foraminifera assemblages in high resolution studies and in selection of material for isotope analyses and their interpretation in cores from inner fjords or silled fjords, where winter-cooled waters may be present.
