Paleoenvironmental changes in the Pacific sector of the Southern Ocean (Antarctica) during the past 2.6 M

Two deep-sea cores (ANTA95-157 and ANTA98-1) were collected in the Pacific sector of the Southern Oceanacross the present-day position of the Antarctic Polar Front Zone (APFZ) to document paleoenvironmentalchanges during the last 2.60 Ma. The stratigraphic framework was established using a combination of diatommarker species, Accelerator Mass Spectrometry (AMS)14C datings, magnetostratigraphy, and oxygen stableisotopes. The study was based on carbon and nitrogen isotopes of diatom-bound organic matter, dry bulkdensity, magnetic susceptibility, carbonates and biogenic silica contents.Large continental inputs were recorded during glacial periods and major iceberg melting occurred at 2.45 Maand during the Middle Pleistocene Revolution (MPR) time interval.Diatom production increased during the Early Pleistocene and remained significant ever since, with the exceptionof the MPR period and immediately before. Lower glacial diatom productivity linked to higher nitrogen utilizationmight have characterized the period between Marine Isotope Stages (MISs) 15-13 (0.6 and 0.5 Ma), whereassucceeding glacial stages experienced an increase of diatom productivity promoted by the inflow of nutrient-richdeep waters. The low diatom production observed during interglacial stage 11 could be explained with asouthward shift (up to 4°) of the Polar Front (PF) with respect to its present position.Paleoproductivity levels have been confirmed as lower than those measured in other sectors of the SouthernOcean, with reduced differences among glacial and interglacial stages.