MODERN FORAMINIFERAL FAUNAS OF THE SOUTHWESTERN TO NORTHERN ICELAND SHELF: OCEANOGRAPHIC AND ENVIRONMENTAL CONTROLS

摘要

Surface sediment samples for analysis of modern fo-raminiferal assemblages were collected from 32 sites on the western and northern Iceland shelf during cruise B997 of the Icelandic ship Bjarni Saemundsson. The purpose of the study is to provide a basis for interpreting the variations in foraminiferal content in late glacial through Holocene sediments from cores at the same sites. Cluster analysis and principal components analysis of the benthic foraminiferal data and associated modern environmental parameters including hydrography, water depth, and sediment characteristics show that large progressive changes in the foraminiferal assemblages coincide with changes in the dominant oceanic surface currents and water masses around Iceland. The western areas of the shelf are overlain by relatively warm and saline Atlantic Water of the Irminger Current. The western shelf fauna is dominated by Cassidulina laevigata and other boreal species, whereas the planktic fauna is dominated by dextrally coiling Neogloboquadrina pach-yderma. In Djupall, off the Northwest Peninsula, and in the shallow nearshore sites on the northern shelf, the boreal elements of the fauna diminish and arctic species become more important. However, the dominant species in these areas are Cibicides lobatulus and Astrononion gallowayi, attesting to winnowing of the shallow shelf areas by currents. In Isafjardardjup, the large fjord indenting the Northwest Peninsula, Cassidulina reniforme and Elphidium excavatum dominate the fauna as a result of cooler waters and more variable salinity conditions. A very large faunal shift is registered in the deep basins of the northern shelf. This faunal shift coincides with large changes in salinity and temperature stratification of the water column, reflecting the presence of the East Iceland Current. The fauna in the deep basins on the northern shelf are dominated by C. neoteretis, an indicator of modified Atlantic Water, and infaunal species that reflect organic fluxes to the seabed: Nonionellina labradorica and Melonis barleeanus, and the arctic species Islandiella norcrossi and I. helenae.