The Arctic pelagic environment is expected to strongly alter due to global climate change. As a consequence, modification of the unicellular plankton species composition and biomass, with consequences to biogeochemical cycling and pelagic food web, is expected. In this study we used meta-barcoding of the V4 region of the 18S rRNA gene to profile eukaryotic microbial communities exported to deeper water layers at the Long-Term Ecological Research Site HAUSGARTEN in the northeastern Fram Strait. We collected sinking particles at ca. 80 to 300 m depths using long-term deployed sediment traps and analyzed selected samples of spring and summer periods from 2000-2011. Acknowledging the limitations and biases of currently used 18S rRNA gene meta-barcoding primers in detecting certain taxa especially from environmental samples, we developed new primer sets and compared them with those already in use. Using the information generated by three different primer sets, the results of our study suggest decreasing trends in the abundances of large-cell phytoplankton (i.e., diatoms) and increasing pico-phytoplankton (Micromonas sp. and haptophytes) during the warm anomaly of 2005-2007. Phylogenetic analyses further revealed the displacement of cold-adapted with warm-adapted phylotypes of Micromonas and haptophytes, which could be related to the warming event. Ecotype-level changes observed in this study do not only suggest changing structures in community composition and ecosystem functioning but also in the biogeography and distribution of some species. These data provided new insights and information on the potential diversity changes and species displacement brought about by the environmental changes occurring in the Arctic Ocean.