Effects of temperature and the amendment of natural organic matter and carbohydrates on growth rates and taxonomic composition of prokaryotic communities of the Weddell Sea were investigated by on-board experiments during the Polarstern expeditions PS111 and PS117. Experiments were conducted in February 2018 (PS111) and in January and February 2019 (PS117). Seawater samples were collected with Niskin bottles at 50-125 m depth and incubated in acid-cleaned 2 L-bottles under different temperature-substrate conditions for 4-5 days. Initial samples and samples after incubation were collected on 0.22 micrometer polycarbonate filters and nucleic acids were extracted using the AllPrep DNA/RNA mini kit (Qiagen). The primer pair 341F (CCTAYGGGRBGCASCAG) and 806R (GGACTACNNGGGTATCTAAT) (Sundberg et al. 2013) was used for PCR amplification of the V3-V4 region of the 16S rRNA gene. The project was funded by the German Research Foundation (DFG) under the grant number PI784/3-1 (CombiBac).