Climate change impacts have brought up the need for a better understanding of the rapidly changing ecosystem of the Arctic. Arctic marine ecosystems, such as around Southampton Island in Hudson Bay, are supported by phytoplankton production. In turn, phytoplankton production, which is influenced by environmental conditions and processes, can impact pelagic and benthic food webs. The goal of this thesis was to determine the physical processes driving phytoplankton production around Southampton Island, Nunavut during summer. Three subgroups of differing physical characteristics of the water column were distinguished: the Northwest Narrows group (well-mixed water connecting Roes Welcome Sound and Frozen Strait), the Hudson Bay group (warmer stratified waters to the south of Southampton Island), and the Foxe group (colder stratified northeastern waters in Foxe Basin and Foxe Channel). The different physical characteristics resulted in contrasting phytoplankton production and phytoplankton bloom stages around the island. In particular, a highly productive phytoplankton bloom supported by mixing and high nutrient availability, was observed in the Northwest Narrows group. Phytoplankton production estimates in the Northwest Narrows group were higher than estimates for Hudson Bay and Foxe Basin, and comparable to those in Hudson Strait. The substantial variability phytoplankton production around Southampton Island highlights the importance of local processes for primary production in the Arctic. This also calls to the necessity for future work to identify similar regions that have the potential to support high phytoplankton production in the Arctic.