The project aims to identify drivers of phytoplankton community structures in Arctic fjords. In particular, I study under which conditions a bloom is dominated by flagellates and under which conditions by diatoms. I will combine multivariate statistics on existing time series data in Greenland and Svalbard (Adventfjorden) to identify potential drivers. I will then test the drivers by experiments in the field at both sites by incubating natural phytoplankton communities with a) different nutrient additions (Silicate, Phosphate, Nitrate), b) addition of Calanus grazers, and c) addition of Phaeocystis inoculum under in situ conditions. In the end of the experiment I quantify the abundances of flagellates and diatoms again in order to quantify the role of the different drivers.