New evidence for the Holocene paleoenvironmental conditions based on sediments recovered from a moraine ridge near the Søstrene Islands, Prydz Bay, East Antarctica

During the 68th Russian Antarctic Expedition (2022/2023), a marine deposit was discovered on a push moraine ridge near an unnamed nunatak east of the Søstrene Islands, Prydz Bay. The deposit, at ~28 m a.s.l. within the Publications Ice Shelf zone, consists of sandy-silty substrate rich in mollusk shells, sponge spicules, and a well-preserved diatom assemblage. Diatom analysis (27 taxa) reveals a flora dominated by sea-ice related (44.6%) with abundant species of genus Fragilariopsis (for example F. curta), indicating cold, ice-influenced neritic conditions. The significant presence of open-ocean diatoms (21.4%), especially Fragilariopsis kerguelensis and neritic open-water (31.3%), for example Thalassiosira margaritae suggests seasonal penetration of open-ocean waters and enhanced oceanic influence during the Early Holocene. Radiocarbon dating of Adamussium colbecki shells yielded calibrated ages of ~8.84 and ~8.29 ka cal BP. Given the ~550-year offset between the median ages and their broad, partly overlapping probability ranges, the dates are interpreted as constraining an interval of marine sediment accumulation rather than a single short-lived depositional event. Incorporation of these sediments into the push moraine records later glacial reworking and readvance; however, the moraine itself is not directly dated, and a late Holocene formation age remains a tentative regional correlation. These new onshore data bridge the gap between offshore marine cores and terrestrial lake archives and refine the paleoenvironmental reconstruction of the Prydz Bay sector.