Svalbard is one of the most extreme environments on Earth with permanently low temperatures and almost 4 months of darkness. Surface sediments (0-2 cm depth) and surface seawater was sampled in Isfjorden. Four stations within 1 km distance were visited in December 2017, February 2018, May 2018, December 2018, April 2019 and September 2019. To investigate seasonal changes of the bacterial communities, 16S rRNA genes were amplified from extracted DNA and sequenced using primers targeting the V3-V4 region.