Distribution Patterns and Morphology of Islandiella norcrossi (Cushman) in the Upper Quaternary Deposits of the Laptev Sea

Resumo

The ecology and taxonomy of Islandiella norcrossi (Cushman, 1933), a typical representative of the Arctic calcareous benthic foraminifers, are analyzed based on microfossils from the Late Pleistocene-Holocene deposits of the Laptev Sea. This species is distributed on the shelf and continental slope of the Arctic seas, and indicates normal marine conditions with a seasonal ice cover and cold Arctic water masses. The species is also associated with a high seasonal productivity in sea-ice marginal zone. Tests are abundant in the Laptev Sea sediments, and show some variability in the size and shape of chambers, which was possibly caused by harsh environmental conditions of the Arctic (limited period of growth and reproduction); aberrant forms with an additional aperture being also present. The population contains tests of macrospherical and microspherical generations, as well as juveniles.