This dataset provides abundance data for polychaete families determined from sediment samples collected around the Antarctic Peninsula (PS 81, seven stations, 22 Jan–18 Mar 2013), in the southeastern Weddell Sea (PS 96, six stations, 06 Dec 2015–14 Feb 2016) and the northwestern Weddell Sea (PS 118, three stations, 09 Feb–10 Apr 2019). During the three expeditions a minimum of three samples (cores) were collected at each station with a MUC10 multicorer or a giant box corer (in this case subsampled with MUC10 core liners). Sediment cores from station 037, 048 (PS 96) and 006, 008, 038 (PS 118) were sliced into depth layers 0–1 cm, 1–2 cm, 2–3 cm, 3–4 cm, 4–5 cm, 5 cm–bottom. Sediment cores from station 241 (PS 81) and 017, 026, 061, 072 (PS 96) were sliced into depth layers 0–2 cm, 2–5 cm, 5 cm–bottom. For the remaining six stations from PS 81 the whole core was used (unsliced). Sediment samples were preserved in 4%-borax-buffered formaldehyde solution prior to sieving and counting (detailed methods in Weith et al. under review, Säring et al. 2022). Stacked sieves with a mesh size of 500 µm and 1000 µm were used for samples from PS 96, PS 118 and station 241 from PS 81. Samples of the remaining six stations from PS 81 were sieved over a 500-µm sieve. Abundance for each polychaete family is presented per depth layer (note different slice volumes) as counts (note different core diameters) and as ind./m². Data from different sieve size fractions are available upon request. Polychaete communities included individuals from 34 families. The polychaete abundance data are part of a larger ecological study on meio- and macrofauna communities and their relation to environmental conditions and remineralisation at the sediment-water interface (see "Supplement to", "Related to" and "Further details" below). Sediment cores from which polychaete abundance data are deposited here were also used for microcosm incubations: Untreated incubations (Benthic Ecosystem Functioning Experiment BEFEx) and incubations with and without microalgae addition (Algae Feeding Experiment AFEx). Cores from BEFEx and AFEx without algae are labeled with NT (not treated), cores from AFEx with algae are labeled as T (treated).

This study was supported by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (Grants AWI_ PS81_03, AWI_PS96_02, AWI_PS118) and by the German Research Foundation DFG, SPP 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas (Projects LI2313/3-1, LI 2313/6-1 and VE 260/10-1).