Modeling variations of the seasonal cycle of plankton production: the Labrador Sea, Labrador Shelf and Hamilton Inlet

Abstract

Changes in phytoplankton production can have a profound impact on the marine ecosystem. One factor that can affect phytoplankton populations is change in stratification of the water column. Climate changes over the Labrador Sea and Labrador Shelf have significantly altered the stratification of these regions. Regulation of the Churchill River flow, due to hydroelectric development, has influenced the stratification of Hamilton Inlet of coastal Labrador. Observations in the Labrador region are inadequate to determine the influence of stratification variability on the marine ecosystem. The goal of this research was to integrate the available data with simplified ecosystem models to enhance our understanding. To investigate the sensitivity of seasonal plankton dynamics to climate-induced changes in stratification of the Labrador Sea and Shelf, distinct periods of natural variability were used to force the model. The model was also used to investigate the impact of altering freshwater flow into Hamilton Inlet before and after hydroelectric development. The model exhibited distinct seasonal plankton dynamics that match the existing chlorophyll measurements from each region reasonably well. It was found that in the Labrador Sea and Shelf, when the North Atlantic Oscillation index was positive the spring bloom was delayed. The total annual phytoplankton biomass in the Sea increased while on the Shelf it remained unchanged. In Hamilton Inlet after hydroelectric development, the model showed that the timing of the spring bloom remained unchanged but the total annual biomass decreased. The primary production in the Inlet also decreased after 1976 by about 25%, while for the Shelf there was little difference in primary production.