Global warming has led to an acceleration of Arctic sea-ice decline since 2001, resulting in an increase in the open water period and an increase in primary production. The response of the prokaryotic communities to these environmental changes and to the expected intensification of phytoplankton bloom is still poorly described. This project investigated the dynamic of prokaryotic communities composition in the free-living fraction by Illumina sequencing on a weekly scale in the bottommost layer of the sea ice (0-10 cm) and in the upper water-column (up to 60 m depth) during ice retreat in the Baffin Bay (April 20th to July 27th 2016). The aims of this study were to assess (i) the dynamic of prokaryotic community structure in both seasonal sea ice (i.e. which forms during freeze-up period and undergoes complete melt during spring and summer) and the upper water-column during the phytoplankton bloom, (ii) to compare the total and the metabolically-active fraction of the prokaryotic communities by sequencing the reverse-transcribed total RNA and (iii) to identify the most responsive species among the prokaryotes.