Regional differences and inter-annual variability in the timing of surface phytoplankton blooms in the Labrador Sea

Abstract The annual phytoplankton bloom is an important marine event and its inter-annual variability can be used to monitor changes in the pelagic ecosystem. In this context, the use of a bio-regionalization analysis to objectively identify ocean areas that differ in their biological characteristics and environmental conditions may be useful to disentangle the functioning of the ecosystem. In this work, satellite surface chlorophyll- a concentration observations were used to obtain a bio-regionalization of the Labrador Sea (LS). Specifically, bioregions were defined using a K-means cluster analysis applied on the satellite time-series of chlorophyll- a concentration. Finally, the resulting biologically regionalization was used in conjunction with simulated data from a state-of-the-art ocean circulation model (NEMO) to investigate difference in spring bloom timing response across the Labrador Sea (LS). Chlorophyll- a seasonal cycle in the LS varies markedly between two neighboring but distinct bioregions: the north (>60 °N) and the south (