Genomic-to-space measurements reveal large-scale ocean nutrient stress.

Abstract

Phytoplankton growth and ocean primary production depend on a nutrient supply that fluctuates across seasonal to millennial timescales. Because surface nutrients and phytoplankton biomass recycle rapidly, they obscure the large-scale pattern of nutrient stress. Here, we integrate a satellite-derived index of phytoplankton physiology with hydrographic observations, omics biomarkers, and nutrient-addition experiments to understand the drivers of ocean nutrient stress. A clear biogeography emerges. Nutrient stress tracks nutricline depth and is stronger in nitrogen- than phosphate-limited waters, peaking where cells exploit rarer alternative nutrients. Seasonal variability dominates, but there are also clear signatures of major climate modes. Over the past two decades, surface warming has broadly intensified nutrient stress. A key exception is in southern hemisphere oligotrophic regions, where enhanced nitrogen fixation appears to offset stratification effects. This synthesis of hydrography, genomics, and satellite physiology exposes contemporary, climate-linked shifts in the large-scale distribution of phytoplankton nutrient stress.