Comment on egusphere-2025-6290

Abstract. Benthic foraminifers show distinct temporal and spatial distribution patterns in the Central Arctic Ocean (CAO) demonstrating their potential to provide robust age constraints and to address paleoceanographic change in the Pleistocene. Several benthic foraminifer bioevents have been previously reported from the upper and middle Pleistocene that are here critically evaluated by studying three sediment cores from the Mendeleev and Lomonosov ridges and analysing published data sets. Based on this data bioevents are defined by using absolute abundances of species in the >63 µm grain size fraction, whereas relative abundances are considered not reliable because taphonomic processes such as disintegration and/or dissolution overprint the original assemblage composition. Bioevents are calibrated to lithological horizons and then linked to Quaternary subseries and marine isotope stages based on available independent stratigraphic data. Three calcareous bioevents can be defined in the Brunhes Chron (Middle Pleistocene): (1) the highest common occurrence of Bolivina arctica (~MIS 9) at the top of lithological unit L in brown bed B 7, (2) the lowest common occurrence of Oridorsalis umbonatus at the base of brown bed ?B 4 (~MIS 7), and (3) the acme of Bulimina aculeata (~MIS 7) in brown bed ?B 4 in water depths of less than ~ 2000 m. The lowest common occurrence of Oridorsalis umbonatus is coeval with the base of the acme of Bulimina aculeata at shallow sites (