Abstract

A palynological investigation was undertaken on the upper 29 m of sediment at Ocean Drilling Program (ODP) Site 887, spanning the last 430 000 years (i.e., isotopic stages 12 to 1). Pollen and dinocyst assemblages reveal a major ecostratigraphical boundary at the Middle–Late Pleistocene transition. The Middle Pleistocene pollen data document the occurrence of a spruce forest vegetation in the source area, likely located on the adjacent Alaskan coast, whereas the Late Pleistocene is marked by higher inputs of pine, shrub, and herb taxa, suggesting predominant inputs from a more open landscape. The Middle Pleistocene is characterized by a low diversity in dinocyst assemblages, which are dominated by Operculodinium centrocarpum, whereas the Late Pleistocene is marked by the significant occurrence of Pentapharsodinium dalei, Pyxidinopsis reticulata, and by high percentages of Brigantedinium spp. Such assemblages suggest open oceanic and cool temperate conditions during the Middle Pleistocene, changing toward generally colder and less saline conditions during the Late Pleistocene. In addition, large fluctuations in the dinocyst assemblages during the Late Pleistocene are recorded in phase with the main shifts in the isotopic stratigraphy. A new dinocyst taxon, Spiniferites alaskensis sp. nov., exclusively recorded in sediments of the isotopic substage 5e, is described herein.

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