Figure: Fine-scale global variation of surface phosphate. Surface phosphate is here measured using high-sensitivity techniques revealed a previously unrecognized low latitude differences in phosphate drawdown.
Surface ocean phosphate is commonly below the analytical detection limit using the standard auto-analyzer technique. Thus, we know little about the geographic variation in phosphate across most low latitude regions. As the result of a global collaboration, a recent study in Science Advances combined phosphate measurements using high-sensitivity methods and produced a detailed map of surface phosphate (see figure). This revealed several previously unrecognized low phosphate areas. For example, we detect large regions of really low phosphate in the western North and to a lesser extent South Pacific Ocean. Atmospheric iron input and nitrogen fixation are commonly described as regulators of surface phosphate but we show that shifts in the elemental stoichiometry of the vertical nutrient supply play an additional role. Multiple past studies as well as climate models have suggested that the availability of phosphate is a first-order driver of ocean biogeochemical changes. However, we find that marine ecosystems are more resilient to phosphate stress than previously thought. Our study demonstrates the importance of accurately quantifying nutrients at low concentrations for understanding the regulation of ocean ecosystem processes and biogeochemistry now and under future climate conditions.