Future Changes in Biological Activity in the North Pacific due to Anthropogenic Forcing

Many studies have examined the physical changes expected in the environment as a result of anthropogenic forcing. These physical changes will have an effect on ecosystems as well. In this study, a nitrogenphytoplankton-zooplankton (NPZ) model is used to examine the effects of environmental changes on primary productivity in the North Pacific ocean. The physical variables considered are mixed layer temperature and depth, solar insolation, and large-scale upwelling. The changes in these fields by the 2090s are taken from a coupled ocean-atmosphere general circulation model forced by projected atmospheric CO and sulfates, then applied to the NPZ biological model. The result is a 20-30% reduction in primary productivity in a belt of longitudes across the North Pacific. This happens because the region where spring blooms occur moves northwards in response to the anthropogenic changes. The region left behind (which had spring blooms in the 2000s, but does not in the 2090s) is less productive when averaged over a year. In other regions, productivity increases as warmer surface waters enable higher growth rates. Changes in mixed layer temperature and depth account for almost all the changes in productivity; model-predicted changes in surface insolation and large-scale upwelling have little impact.