The subpolar North Atlantic is an important region in which to study late Neogene paleoceanographic and climatic change. The region is among the most sensitive to glacial-interglacial sea-surface temperature variations (e.g., CLIMAP, 1981) and has a major influence on conversion of surface waters to deep waters and, hence, the global thermohaline circulation (e.g., Broecker and Denton, 1989). Documenting tectonic- to millennial-scale paleoceanographic changes in this region associated with the late Neogene evolution of Northern Hemisphere glaciation is a major goal of Ocean Drilling Program (ODP) Leg 162.
The North Atlantic and Nordic Seas region sampled during Leg 162 ranges from temperate to polar waters. A southeast-northwest transect of subpolar North Atlantic sites (Jansen, Raymo, Blum, et al., 1996) includes high sedimentation-rate locations on Feni Drift, Bjorn Drift, and Gardar Drift (Fig. 1; Table 1). These high sedimentation-rate sites (drilled with the advanced hydraulic piston corer) allow for detailed comparison of geographic synchroneity and asynchroneity among planktonic foraminifer datum levels. Site 982 on the Rockall Plateau reached lower Miocene sediments, providing a nearly complete Neogene sediment sequence for the subpolar North Atlantic. Together with sites from the Nordic Seas, these sites provide insights on subpolar North Atlantic paleobiogeography during the Neogene and the (a)synchroneity of planktonic foraminifer datum levels across the subpolar North Atlantic.
Previous work in this region includes sites drilled on Deep Sea Drilling Project (DSDP) Leg 12 (Hayes, Pimm, et al., 1972), Leg 38 (Talwani, Udintsev, et al., 1976), Leg 81 (Roberts, Schnitker, et al., 1984), and Leg 94 (Ruddiman, Kidd, Thomas, et al., 1987). Neogene planktonic foraminifer paleobiogeography of the subpolar North Atlantic shows progressive reduction in diversity and development of endemic subpolar faunas in the late Miocene and continuing in the late Pliocene (Berggren, 1972; Poore and Berggren, 1975; Poore, 1979; Huddlestun, 1984; Weaver, 1987; Raymo et al., 1987; Spencer-Cervato et al., 1994). These changes are associated with the progressive cooling of the high northern latitudes during the Neogene and the development of Northern Hemisphere glaciations (e.g., Shackleton et al., 1984; Ruddiman, Kidd, Thomas, et al., 1987; Jansen et al., 1988; Raymo et al., 1990).
Whereas the subpolar North Atlantic featured the accumulation of calcareous sediments throughout the Neogene, calcareous sediment preservation in the Nordic Seas (Greenland, Iceland, and Norwegian Seas) began much later, by ~1 Ma (Jansen et al., 1988; Spiegler and Jansen, 1989; Spiegler, 1996). Because calcareous sediment preservation commenced within the Quaternary, planktonic foraminifer faunas are dominated by Neogloboquadrina pachyderma (sinistral), although rare incursion of warmer water species is documented in the Pliocene sediments of the Nordic Seas and Arctic Gateway region (Spiegler and Jansen, 1989; Spiegler, 1996).
The progressive development of cold surface-water conditions in the high-latitude North Atlantic has led to the need for two planktonic foraminifer zonation schemes for the late Miocene to Holocene, one for the subpolar North Atlantic (Weaver and Clement, 1986) and one for the Nordic Seas (Spiegler and Jansen, 1989). The tropical and subtropical zonations (Blow, 1969, 1979; Bolli and Saunders, 1985) have limited value in middle to high latitudes because many of the warm-water forms on which these zonations are based are not found at higher latitudes. Zonations for the upper Miocene to Holocene sediment sequence in the subpolar North Atlantic and Nordic Seas are based mainly on species within the neogloboquadrinid and globorotalid groups (Berggren, 1972; Poore and Berggren, 1975; Poore, 1979; Weaver and Clement, 1986, 1987; Weaver, 1987; Hooper and Weaver, 1987; Spiegler and Jansen, 1989). In this study, the subpolar zonation of Weaver and Clement (1986) is used for Sites 980-984, including the upper Miocene to Holocene at Site 982. The Nordic Seas zonation of Spiegler and Jansen (1989) is used for Sites 985-987 and 907.
The generally high abundance and good preservation, plus the continuous sequences obtained in the subpolar North Atlantic, provide excellent material for planktonic foraminifer studies at Feni Drift Sites 980 and 981, Gardar Drift Site 983, and Bjorn Drift Site 984. The oldest age reached among these drift deposits is ~4.8 Ma at Feni Drift Site 981 (~320 meters below seafloor [mbsf]). However, Rockall Plateau Site 982 reached an age of ~18.4 to 19.2 Ma at ~605 mbsf. Feni Drift Site 981 (early Pliocene to Holocene) and Rockall Plateau Site 982 (early Miocene to Holocene) are, therefore, particularly useful for studies that focus on the Neogene.