A summer phytoplankton bloom triggered by high wind events in the Labrador Sea, July 2006

The mechanisms of nutrient resupply for an episodic phytoplankton bloom observed in the central Labrador Sea in July 2006 were investigated. Two physical processes, mixed-layer deepening and Ekman pumping, are proposed to account for the implied nutrient replenishment. The nutrient flux and chlorophyll concentration before and during the bloom were estimated from a simple coupled nitrate-phytoplankton model. The model results show that the enrichment of nutrients in the euphotic layer and the subsequent bloom were related to two wind events (storms) in the period July 7-10. As the mixed layer deepened, nutrient from below the nitricline were entrained into the euphotic zone. The Ekman pumping, which was most intense at the storm centre, enhanced the transport of the nutrients by raising the nitricline. However, Ekman pumping alone was not able to transport sufficient nitrate to the euphotic layer to support the observed phytoplankton bloom.