Dinoflagellate cyst analysis of the upper Pliocene-Pleistocene succession at Site 986 provides information that aids age interpretations of the seismic sequences. This information can also be used to interpret changes in depositional environments and paleoceanographic conditions along the western Svalbard margin during the last 2.6 Ma.
More than 290 taxa have been identified from Hole 986C, and 208 different taxa have been recovered from Hole 986D. Most of these taxa are reworked from older Neogene, Paleogene, and Mesozoic deposits. The low thermal maturity and good preservation of the reworked palynomorphs suggest a provenance area on the central or eastern Barents Shelf and/or eastern Svalbard. Most probably the reworked material followed a westerly drainage route into the Storfjorden Trough and was subsequently transported with the West Spitsbergen Current to the present deposition site.
The biostratigraphic occurrence of selected Pliocene-Pleistocene dinoflagellate species, together with data from magnetostratigraphy (Channell et al., Chap. 10, this volume) and foraminifers (Eidvin and Nagy, Chap. 1, this volume), provides information on the ages of the seismic sequences recognized at the drill site. The following events, among others, have been considered: (1) The LADs of Selenopemphix brevispinosa at 928.34 mbsf and Invertocysta lacrymosa at 909.14 mbsf, suggesting ages between 2.6 and 2.7 Ma for the oldest parts of the drilled succession; (2) an acme of Filisphaera filifera s.l. at 804.84 mbsf, possibly giving an age in the range of 1.9-2.1 Ma based on correlation with Hole 911A; (3) the LAD of Sumatradinium pliocenicum at 564.44 mbsf, indicating an age not younger than 1.65 Ma; (4) the LAD of Amiculosphaera umbracula at 333.53 mbsf, indicating an age of 1.5? Ma; and (5) the LAD of Operculodinium israelianum at 122.18 mbsf, suggesting an age of 0.73 Ma.
The distribution of dinoflagellate cysts at Site 986 is influenced by depositional processes attributed to the formation of a fan complex near the mouth of the Storfjorden Trough and climatological and oceanographic processes controlling the glacial buildup in the Barents Sea. Fluctuations in the relative abundance of various taxa and variations in the G:P ratio can be used to identify changes in the paleoenvironments through the upper Pliocene-Pleistocene succession. The dinoflagellate assemblages suggest a relatively strong influence of the North Atlantic Current during periods of the late Pliocene-early Pleistocene and that relatively warm water was transported along the West Spitsbergen Current toward the Fram Strait. These periods of warm-water inflow must have alternated with periods of continuous sea-ice cover in the Arctic Ocean. The younger Pleistocene sediments are also characterized by marked fluctuations in the abundance of in situ dinoflagellate cysts. Intervals with low abundances are attributed to glacial stages. On the other hand, levels with increased abundances and diversities, combined with the occurrence of typical outer neritic to oceanic species, suggest periods with inflow of warmer North Atlantic surface-water masses. These warm events are noted at ~1.4-1.5, 1.2, and 0.5 Ma. Although the fluctuations in the distribution of dinoflagellates in the upper Pliocene-Pleistocene succession is clearly related to glacial-interglacial cycles, the low- resolution sampling at Site 986 does not allow further identification of high-frequency cycles through the late Neogene.