Middle Eocene-late Oligocene climate variability: Calcareous nannofossil response at Kerguelen Plateau, Site 748

A major deterioration in global climate occurred through the Eocene–Oligocene time interval,characterized by long-term cooling in both terrestrial and marine environments. During thislong-term cooling trend, however, recent studies have documented several short-livedwarmingand cooling phases. In order to further investigate high-latitude climate during these events, wedeveloped a high-resolution calcareous nannofossil record from ODP Site 748 Hole B for theinterval spanning the late middle Eocene to the late Oligocene (~42 to 26 Ma). The primarygoals of this study were to construct a detailed biostratigraphic record and to use nannofossilassemblage variations to interpret short-term changes in surface-water temperature andnutrient conditions. The principal nannofossil assemblage variations are identified using atemperate-warm-water taxa index (Twwt), from which three warming and five cooling eventsare identified within the middle Eocene to the earliest Oligocene interval. Among these climatictrends, the cooling event at ~39 Ma (Cooling Event B) is recorded here for the first time.Variations in fine-fraction δ18O values at Site 748 are associated with changes in the Twwt index,supporting the idea that significant short-term variability in surface-water conditions occurredin the Kerguelen Plateau area during the middle and late Eocene. Furthermore, ODP Site 748calcareous nannofossil paleoecology confirms the utility of these microfossils forbiostratigraphic, paleoclimatic, and paleoceanographic reconstructions at Southern Oceansites during the Paleogene.