1.6 Ma biostratigraphy, oxygen isotope record and paleoceanography of the IODP 353 Site U1443 in the equatorial eastern Indian Ocean

Paleoceanographic studies rely heavily on an accurate stratigraphy as well as the interpretation of the oxygen isotope (δ¹⁸O) records generated from microfossils. In this study, we present new planktonic foraminiferal assemblage and stable oxygen isotope records of both planktonic and benthic foraminifera from sedimentary deposits at the IODP Site U1443 on the northern Ninety East Ridge in the equatorial eastern Indian Ocean. Five planktonic foraminiferal datums were identified, which allowed us to refine the Pleistocene biostratigraphical sequence of the site. Our benthic δ¹⁸O record was tuned to that of the LR04 stack with consideration of the planktonic foraminifera and nannofossil datums, volcanic ash, and geomagnetic reversal events. This led to a refined stratigraphic framework for 1.6 Ma at the IODP Site U1443. We focus our discussion on the paleoceanographic and paleoclimatic interpretations of the newly obtained δ¹⁸O records. The synchronous variations of the U1443 planktonic δ¹⁸O record with the obliquity fluctuations during the 1.6 Ma – 0.8 Ma point to the presence of a signal of high-latitude insolation in the surface waters of the study area. By contrast, from 0.8 Ma, the δ¹⁸O record exhibits distinct precession signal, as observed in the South China Sea, which we interpret as being influenced by regional hydroclimate dynamics, such as monsoons. This study therefore provides new data for investigating possible mechanisms that link the high and low latitudes into the early Pleistocene.