Global declines in net primary production in the ocean color era

The majority of heat associated with climate change has been absorbed in the sunlit surface ocean where phytoplankton carry out half of biospheric net primary production (NPP). The physical entrainment of nutrients from depth into the surface constrains NPP across most of the ocean, therefore it has been widely hypothesized that a warmer and more thermally stratified ocean will diminish NPP. As phytoplankton are the dominant driver of ocean color, the satellite remote sensing record is the best approach to assess global NPP trends. Here we show that statistically significant decreases in NPP have occurred in almost half of the ocean and these changes are dominated by declines in the tropical and subtropical stratified ocean. A deeper analysis confirms that strengthening nutrient limitation is largely driving declining NPP. Climate-mediated shifts in NPP represent a fundamental perturbation to biogeochemical cycles that can further weaken global fisheries.