Description: Since the 1990s the AWI conducts studies on phytoplankton ecology at various locations in the central Arctic Ocean, the Greenland Sea and the Fram Strait onboard the ice going research vessel Polarstern. These studies provide valuable insight into the pelagic Arctic ecosystem. However, plankton abundance and composition were determined only sporadically and only few biogeochemical components were analysed. Considering the rapid changes of environmental conditions due to increasing temperatures, sea ice loss and ocean acidification, a comprehensive view of their impact on pelagic biological processes and the consequences for organic matter cycling is essential for our understanding of Arctic ecosystems. Thus a new group - Plankton Ecology and Biogeochemistry in a Changing Arctic Ocean (PEPBCAO) - established at the AWI studying the pelagic system in greater detail. The aim of this group is to complement the measurements of bulk variables and phyto- and zooplankton abundances by molecular assessment of the phytoplankton diversity including pico- and nanoplankton, allowing to better quantifying the intrusion of invading species into the polar habitat. Point measurements during cruises will serve as ground-truthing data to create basin wide satellite images, focussing on the quantitative estimation of phytoplankton functional types, which can serve as an input for modelling approaches. Changes in the composition of organic matter are investigated by molecular analyses and together with abundance and activity of zooplankton key species this will improve our ability of estimating carbon export under climate change. Beside the Central Arctic, one focus of the group will be the ‘AWI Hausgarten Deep Sea Monitoring Station’ in the Fram Strait off Svalbard. These data will be integrated in the existing data sets of the Arctic Ocean and this will provide a more detailed view of the changing pelagic system in the transition region between the central Arctic Ocean and the North Atlantic Ocean and first results will be presented.