The high-latitude planktonic foraminiferal associations are low-diversity faunas composed of long-ranging species. In general, it is not possible to apply the standard zonations established for low latitudes (Blow, 1969, 1979; Bolli and Saunders, 1985) or for northern temperate regions (Berggren, 1972; Poore and Berggren, 1975; Poore, 1979; Weaver and Clement, 1986) because the index fossils used for these zonal definitions are often absent in high-latitude assemblages. Studies of Ocean Drilling Program (ODP) Leg 104 sites on the Vøring Plateau in the Norwegian Sea have produced a local high-latitude Neogene zonation (Spiegler and Jansen, 1989; Spiegler, 1996) that is useful for comparison with Site 986. Data from ODP Leg 151 sites from the Fram Strait and the Yermak Plateau are also applicable (Spiegler, 1996).
Planktonic foraminifers are found in 80% of the samples in the interval from Sample 162-986D-28R-1, 30-36 cm (647.72 mbsf), through 54R-1, 29-36 cm (897.62 mbsf). The interval from 897.62 mbsf to the base of the drilled succession (Sample 162-986D-60R-1, 29-36 cm, 955.32 mbsf) is barren of planktonic foraminifers. In the 250-m-thick interval containing planktonic foraminifers, the assemblage exhibits highly variable abundance, fluctuating from rich faunas to intervals that are poor in or barren of planktonic foraminifers. Except in a few samples, most specimens are well preserved and show no signs of reworking.
The assemblage consists mainly of Neogloboquadrina atlantica (sinistral) and Globigerina bulloides. N. atlantica (dextral) occurs sporadically, mainly in the upper part of the section. Neogloboquadrina pachyderma (sin., mainly unencrusted form), N. pachyderma (dex.), Turborotalita quinqueloba, and Globigerinita glutinata occur in small numbers in some intervals throughout the succession (Fig. 3).
In the high-latitude Neogene, N. atlantica (sin.) is indicative of the Neogloboquadrina atlantica (sin.) Zone, spanning Pliocene to latest Miocene age (Spiegler and Jansen, 1989). The entire carbonate-bearing sequence is assigned to the N. atlantica (sin.) Zone. This zone is also rich in G. bulloides. On the Vøring Plateau and in the North Atlantic, the last occurrence (LO) of N. atlantica (sin.) is no younger than 2.4 Ma (Weaver and Clement, 1986; Spiegler and Jansen, 1989; Channell and Lehman, Chap. 8, this volume). The LO of N. atlantica (dex.) is close to the Pleistocene/Pliocene boundary (Weaver and Clement, 1986; Spiegler and Jansen, 1989). This species occurs sporadically in the N. atlantica (sin.) Zone of Spiegler and Jansen (1989).
Paleomagnetic data in Hole 986D show that the base of the core is in the Matuyama Chron, which implies an age of <2.6 Ma (Channell et al., Chap. 10, this volume). The calcareous benthic foraminifer Cibicides grossus occurs down to 877.34 mbsf. This also indicates a late Pliocene age for this interval.
The climatic regime in this area during the late Pliocene may be interpreted to comprise episodic ingressions of warm and transitional surface-water masses into a generally cold ocean. The occurrence of N. pachyderma (dex.), T. quinqueloba, and G. glutinata indicates several short, warm to transitional surface-water events. The cold conditions are documented by N. atlantica (sin.) and N. pachyderma (sin.) (Spiegler, 1996). The highly variable abundance of planktonic foraminifers seems also to be typical of alternating glacial and interglacial conditions. At high northern latitudes, planktonic foraminifers are generally less common as a result of low water temperatures and/or dissolution of the calcareous microfossils. Another reducing factor is dilution by large amounts of detrital material and ice-rafted debris (Spiegler, 1996).