Miocene to Holocene planktonic foraminifers from Leg 162 in the subpolar North Atlantic and Nordic Seas reflect the progressive establishment of southeast-northwest surface-water temperature gradients. Lower to middle Miocene sediments in the subpolar North Atlantic can be correlated with subtropical to temperate zonation schemes, consistent with relatively low meridional sea-surface temperature gradients. Increased meridional gradients are indicated since the middle Miocene by the requirement of subpolar zonations. Results from the Nordic Seas sites agree with previous findings that carbonate sediment preservation increased within the Quaternary.
Planktonic foraminiferal datum levels from Sites 981 to 984 are located to the section level, insufficient to resolve glacial-interglacial variations. However, these data are consistent with previous suggestions that several Pliocene-Pleistocene neogloboquadrinid and globorotalid datum levels are synchronous throughout the mid-latitude to subpolar North Atlantic. These include the start of the Acme Zone N. pachyderma (sinistral) at 1.8 Ma, the FO of Gr. inflata at 2.09 Ma, and the FO of Gr. puncticulata at 4.5 Ma (within 5% of their mid-latitude ages). The LO of N. atlantica (sinistral) is delayed relative to its mid-latitude age (2.41 Ma) by 100-200 k.y. The LO of Gr. puncticulata may generally (but not entirely) occur earlier at more northerly sites. During the Miocene at Rockall Plateau Site 982, the LO of N. acostaensis (5.29 Ma), the FO of O. suturalis (15.1 Ma), and the LO of C. dissimilis (17.3 Ma) may be synchronous (within 5% of their published ages) with these events at mid-latitudes.