Studies of phytoplankton ecology and biogeochemical parameters have been carried out with the ice breaking vessel RV Polarstern since the nineties at various locations in the central Artcic Ocean, the Greenland Sea and the Fram Strait, however, plankton abundance and composition were determined sporadically, and only few biogeochemical components were analysed. Since rapid environmental changes due to increasing temperatures, sea ice loss and ocean acidification in the Arctic Ocean are expected, a more comprehensive impression of the impact of the anticipated changes on pelagic biological processes and the consequences for organic matter cycling is desirable. To get more detailed investigations on the pelagic system the new research group PEBCAO was created. The aim of this group is to complement the measurements of bulk variables and samples on phyto- and protozooplankton abundances by a molecular assessment of the phytoplankton diversity, including the pico- and nanoplankton allowing to better quantifying the intrusion of invading species into the polar habitat. The point measurements during cruises will serve as ground-truthing data to create basin wide satellite images focussing on the quantitative estimation of various phytoplankton functional types, which can serve as an input for modelling approaches. Furthermore, investigations on changes in the composition of organic matter (OM) including molecular analysis of OM are carried out and together with abundance and activity of key species in zooplankton will improve the export estimates under climate change. One local focus of this group is the deep-sea long-term observatory HAUSGARTEN of AWI in the Fram Strait off Svalbard, where investigations on plankton ecology and particle flux have been carried out since the 1990. These observations can be used to identify how current observed changes are related in a historical context. Here we present first results of the multidisciplinary approach form the long term observations and the studies carried out during two Polarstern cruises (ARK 24_1&2 and ARK 25_1&2) in the summer of 2009 & 2010, respectively.