Late Miocene-Early Pliocene Planktonic Foraminifera and Palaeoceanography of the North Atlantic
Abstract. Relative abundance variations of planktonic Foraminifera have been studied for the Late Miocene to Early Pliocene time interval of 7.0 to 3.5 Ma from three sites in the North East Atlantic; DSDP607 (41°N), DSDP609 (50°N) and DSDP611 (53°N), Particular attention has been given to the percentage of benthic Foraminifera of total (benthic + planktonic) Foraminifera as an index of dissolution by aggressive bottom waters, and to the percentage of dextral Neogloboquadrina pachyderma of total (dextral + sinistral) N. pachyderma as an index of “Sub-Polar” or warmer waters.
Strong dissolution, probably associated with the northward penetration of aggressive Antarctic Bottom Water, is observed at two of the sites up to and during the initiation of the Messinian “Salinity Crisis” in the adjoining Mediterranean Sea at about 5.8 Ma. All three sites exhibit strong cyclic fluctuations of the percentage of dextral N. pachyderma during the Messinian “Salinity Crisis” interval, from approximately 5.8 Ma to 4.8 Ma. These are interpreted as indicating wide-ranging oscillations of a water mass boundary, analogous to the present-day Polar Front, in the North Atlantic during the “Salinity Crisis”. Following the re-filling of the Mediterranean with normal marine waters at about 4.8 Ma, the dextral form of N. pachyderma, which is more characteristic of warmer waters than the sinistral form, becomes the dominant form and shows less quantitative variation at all three sites throughout the Early Pliocene.