Paleoceanographic turnovers during the Plio-Pleistocene in the southeastern Indian Ocean: Linkages with Northern Hemisphere glaciation and Indian Monsoon variability.

Earth experienced warm temperatures during the Pliocene followed by a substantial cooling that culminated in an ice age climate at the beginning of the Pleistocene. This warmth had a significant impact on global environments and ocean circulation. The collision of the Indian and Eurasian plates further amplified this climatic pattern. The southern Indian Ocean was severely impacted by these changes in ocean circulation and climatic pattern during the Plio-Pleistocene. We reconstruct paleoceanographic turnovers in the southeastern Indian Ocean during the Plio-Pleistocene using benthic foraminiferal assemblages from ODP Sites 752 and 757, combined with relative abundances of selected planktic foraminiferal species and stable isotope ratios (δ18O and δ13C) of surface-dwelling and thermocline planktic foraminifera from Site 757. The influence of southern source Antarctic Intermediate Water (AAIW) since 4.5 Ma is marked by fluctuations in productivity till the intensification of the Northern Hemisphere glaciation (NHG) at ~3 Ma. Our isotopic data provide no evidence for cooling during the 4–3 Ma interval either for upper (Gs. ruber) or lower (M. menardii) mixed-layer waters, at a time when a switch in the source of the Indonesian Throughflow may have occurred. The increased mixed-layer species abundances since 4 Ma suggest oligotrophic conditions at low-latitude Site 757 due to thick mixed-layer coinciding with the constriction of the Indonesian Gateway and intensification of the NHG. The intensification of the NHG and monsoon seasonality caused an enhanced inflow of AAIW in the southeastern Indian Ocean since ~2.5 Ma. • AAIW influenced the southeastern Indian Ocean since ~4.5 Ma onwards, which further enhanced after ~1.8 Ma. • No decrease in Sea surface temperature at Site 757 due to switch in the source of ITF between ~4 and 3 Ma. • The thick mixed-layer at Site 757 was coinciding with the constriction of ITF and intensification of the NHG. • Indian Winter Monsoon was strong during periods of global cooling since ~2.5 Ma onwards. [ABSTRACT FROM AUTHOR]