Deep-sea living benthic foraminifera and ostracoda from the European Arctic margin and the Yermak Plateau during the spring phytoplankton blooms in the Arctic Ocean: distribution, abundance, and standing stocks

The Arctic Ocean is experiencing rapid environmental changes, with current warming rates exceeding the global average. This accelerated warming has triggered profound shifts in sea ice extent, thickness, and seasonal dynamics. As a result, these alterations impacted the timing of phytoplankton blooming, expanded open-water habitats, and modified the timing of primary production with far-reaching implications for benthic-pelagic coupling processes and benthic ecosystems. This study investigates benthic microfaunal communities, particularly benthic foraminifera (Rhizaria) and ostracoda (Crustacea), as they serve as sensitive indicators for contemporary Arctic conditions. Their distribution, abundance, and standing stocks reflect key factors such as organic matter availability, seasonal ice cover, and water mass properties (e.g., salinity and temperature). The materials for this study were collected during the expedition PS92 (ARK-XXIX/1) "TRANSSIZ" (Transitions in the Arctic Seasonal Sea Ice Zone, 19 May – 28 June 2015) aboard the German research icebreaker Polarstern. This six-week mission focused on early spring ecological and biogeochemical processes across the European Arctic margins. The study area covers the eastern flank of the Yermak Plateau and the northern continental slope of the Barents Sea. Sampling water depths ranged from 470 m to 1829 m. The four cores (PS92/19, PS92/27, PS92/31, PS92/39) were collected with a multiple corer (MUC) with an internal diameter of 10 cm (surface area 78,5 cm²). The MUC frame was equipped with a live broadcasting video system that transfers pictures to the ship via glass fibre cable. A Sanyo HD400P camera (10x optical zoom) captured images of under-ice fauna, marine snow in the water column, and phytodetritus originating from the spring blooms. Surface sediment samples were collected and analysed in the 63 and 125 μm size fractions to identify and characterise microfaunal communities. The results will provide a better understanding of how Arctic benthic ecosystems are adapting to a rapidly transforming environment. Additionally, current spring results will provide data that attempts to fill an existing gap in Arctic benthic foraminifera and ostracoda sampling.