Calcareous nannofossil changes during the Mid-Pleistocene Revolution: Paleoecologic and paleoceanographic evidence from North Atlantic Site 980/981

Abstract

New quantitative data on calcareous nannofossil assemblages through 583–1138 thousand years ago (kyr) have been acquired in high sample resolution (2–3ky) at northern Atlantic ODP (Ocean Drilling Program) Site 980/981. Assemblage composition reflects a temperate paleobioprovince suggesting significant influx of warm North Atlantic Current at the site location during the mid-Pleistocene transition, between Marine Isotope Stage (MIS) 35 and 15.Three intervals have been described based on changes in nannofossil composition and abundance fluctuations of taxa. Reticulofenestrids are abundant just in the first interval (MIS 35–22), which is also characterised by the absence of Gephyrocapsa (>4μm) and C. pelagicus s.l., the latter occurring in upper MIS 24 only. The second interval corresponds to the expanded warm MIS 21 that is accompanied by high carbonate content, absence of both nannofossil reworking and ice rafted debris (IRD), higher abundance of C. leptoporus (5–8μm) and H. carteri, and absence of C. pelagicus s.l. and medium gephyrocapsids. The third interval (MIS 20–15) records the occurrence of C. pelagicus s.l. and medium Gephyrocapsa, generally higher abundance and higher amplitude fluctuations of helicoliths, and absence of reticulofenestrids. The major changes in nannofossil assemblages seem to be the result of combined paleoenvironmental factors related to sea surface water features (temperature and nutrient availability, sea-ice cover) and possibly to deep and intermediate water production of both Northern and Southern Hemisphere origin during glacial and interglacial phases. Complex inter-relationships between environmental parameters and evolutionary/ecological factors are inferred to explain the patterns of Coccolithus pelagicus subspecies, whose distribution and abundance fluctuations are compared with the available patterns of Turborotalia quinqueloba and Neogloboquadrina pachyderma (left coiled) at Site 980 and with the C. pelagicus subspecies patterns from North Atlantic DSDP (Deep Sea Drilling Project) Site 607 and South Atlantic ODP Site 1090.Data collected provide additional information on stratigraphic distribution of selected taxa; the First Occurrence (FO) of Gephyrocapsa omega is confirmed as a diachronous event, even in the Atlantic Ocean, while the First and Last Common Occurrence (FCO, LCO) of R. asanoi appear as diachronous and synchronous events, respectively, on a global scale.