In three sampling campaigns between 2021 and 2022, surface sediments (0-2cm) were collected from one station in Isfjorden, Svalbard (depth ca. 4.5 m; "Station 5": 78°06'36.0''N, 14°21'00.00''E ± 30 m). The sampling was done on two separate days per sampling campaign, during polar night (8th and 11th December 2021), polar day spring (30th April and 2nd May 2022), and polar day summer (29th June and 2nd July 2022). Sediments were sampled using an Ellrott grab (Moncada et al., 2024). The top 2 cm of sediment was subsampled for further analyses. Carbon and nitrogen content from bulk sediments were measured as described in Miksch et al (2021). Briefly, freeze-dried sediments were ground using a Planetary Micro Mill (Pulverisette 7, Fritsch, Idar-Oberstein, Germany). For total carbon and nitrogen analyses, ∼25–50 mg of powdered sediment was packed into 5×9 mm tin capsules (HEKAtech, Wegberg Germany). Prior to organic carbon analysis, inorganic carbon was removed using 1M HCl. Samples were analyzed on a Euro EA-CNS elemental analyzer with thermal conductivity detection (HEKAtech, Wegberg, Germany). Calibration was done with 0.2–2 mg sulfanilamide standards.