CMIP5 model analysis of future changes in ocean net primary production focusing on differences among individual oceans and models

Abstract

Previous modeling studies have shown that global primary production will decrease in the future because stratification caused by global warming will reduce the supply of nutrients from the deep ocean. Previous studies have primarily emphasized the importance of nutrient limitation when explaining changes in primary production; however, phytoplankton growth is actually determined by temperature, light, and nutrient limitations. Moreover, although future changes in primary production differ depending on the area, it is not well understood how these mechanisms differ among oceans. The purpose of this study is to quantitatively evaluate the contribution of each limitation factor to explaining future changes in primary production in individual oceans using nine Coupled Model Intercomparison Project Phase 5 (CMIP5) models. First, for each model, we calculate the temperature, light, and nutrient limitations, which are not directly available from CMIP5 output data. Next, we quantitatively evaluate the main drivers of changes in primary production not only for the global ocean, but also separately for low latitudes, the North Atlantic, the North Pacific, the Arctic, and the Southern Ocean. Via a quantitative evaluation of the limitation factors of primary production, we show that, in addition to nutrient limitation, future changes in primary production due to global warming are controlled by warming-induced enhancement of phytoplankton growth and decreasing biomass caused by enhanced grazing. Moreover, we show that future changes in primary production and its mechanisms differ among the various ocean basins.