Benthic prokaryotic cell densities from Polarstern expedition PS138 to the Central Arctic Ocean during August-September 2023

Undisturbed sediment samples were obtained with a TV-guided multiple corer (TV-MUC). Upon retrieval of the MUC, the overlying water was carefully removed from each core and the upper few centimeters of sediment were cut using a steel plate and a custom-made plastic ring into the following depth horizons: 0-1 cm, 1-5 cm, 5-10 cm. For the determination of prokaryotic cell abundances, 2 ml sediment were fixed in 9 ml formaldehyde/seawater at a final concentration of 2-4% formaldehyde and stored at 4°C. Benthic prokaryotic cell abundances were determined using the Acridine Orange Direct Count (AODC) method (Meyer-Reil, 1983, doi:10.1007/BF00395813) following the protocol described in (Boetius and Damm, 1998, doi: 10.1016/S0967-0637(97)00052-6; Hoffmann et al., 2017, doi:10.3389/fmicb.2017.00266). For 0-1 cm: 3 biological replicates, and 2 technical replicate filters per sample were counted. A total of 50 grids or at least 500 cells were counted per filter. For 1-5 cm: 2 biological replicates, and 2 technical replicate filters per sample were counted. A total of 50 grids or at least 250 cells were counted per filter.For 5-10 cm: 1 biological replicate, and 2 technical replicate filters per sample were counted. A total of 50 grids or at least 100 cells were counted per filter. Because cell numbers were so low in the deeper sediment layers, these numbers need to be treated with caution.