Global warming poses new threats to marine ecosystems since rising seawater temperature potentially induces cascading effects in biogeochemical cycles and food webs. Heterotrophic bacteria are the main producers of CO2 in the ocean, thereby counteracting the biological drawdown of CO2 by primary production. In Antarctic marine systems, low seawater temperature, and the low availability of labile organic matter are major environmental constraints on bacterial growth and degradation activity. However, temperature and the availability of resources for heterotrophic bacteria undergo considerable change induced by climate warming combined with subsequent ice melt and changes in primary productivity. This project aims to test single and combined effects of temperature and organic matter availability on Antarctic marine bacterioplankton. To investigate bacterioplankton community composition and activity, DNA and RNA were extracted from filtered water samples collected at different depths in the upper 100 m of the water column during the Polarstern cruise PS111 to the Weddell Sea. The V3-V4 hypervariable region of the 16S rRNA and 16S rRNA gene was sequenced on the Illumina MiSeq platform. For quality assurance a mock community was included in the sequencing project. The project was funded by the DFG in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas" SPP 1158 by the grant PI784/3-1.