| Summary: | No abstracts are to be cited without prior reference to the author. Continental shelf waters from the Labrador Sea to the Mid-Atlantic Bight experienced significant freshening in the late 1990s, likely caused by increasing glacial melting and enhanced precipitation and river runoff at higher latitudes (as a result of climate change). The freshening of the ocean can alter circulation and stratification of shelf waters and may influence the phytoplankton dynamics and ecosystem productivity. We used a 3-D coupled biological-physical model to examine the influence of freshening on the timing and magnitude of phytoplankton blooms and primary productivity in the Gulf of Maine/Scotian Shelf region. The model captured the general pattern of westward propagation of spring phytoplankton blooms from the Scotian Shelf to the western Gulf of Maine, consistent with the observed increasing sea surface salinity and associated decreasing stability of the water column. By adjusting the boundary conditions in the numerical experiments, the model showed that increased freshening can further enhance the spatial gradients in timing by stimulating earlier blooms upstream (the Scotian Shelf), but has less impact downstream (the western Gulf of Maine). The model results suggest that surface water freshening may impede winter convection and decrease nutrient supply from deep water to the surface, thus influencing the overall seasonal primary productivity.
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