Dissolved organic phosphorus concentrations in the surface ocean controlled by both phosphate and iron stress

Dissolved organic phosphorus (DOP) has a dual role in the surface ocean as both a product of primary production and as an organic nutrient that fuels primary production and nitrogen fixation, especially in oligotrophic gyres. Although poorly constrained, the geographic distribution and environmental controls of surface ocean DOP concentrations influence the distributions and rates of primary production and nitrogen fixation in the global ocean. Here we pair DOP concentration measurements with a metric of phosphate stress, satellite-based chlorophyll a concentrations and a satellite-based iron stress proxy to explore their relationship with upper 50 m DOP stocks. Our results suggest that phosphate and iron stress work together to control surface ocean DOP concentrations at basin scales. Specifically, upper 50 m DOP stocks decrease with increasing phosphate stress, while alleviated iron stress leads to either surface DOP accumulation or loss depending on phosphate availability. Our work extends the relationship between DOP concentrations and phosphate availability to the global ocean, suggests a linkage between marine phosphorus cycling and iron availability and establishes a predictive framework for DOP distributions and their use as an organic nutrient source that supports global ocean fertility. Production and consumption of dissolved organic phosphorus in the surface ocean is controlled by the interplay between phosphate and iron stress, according to global analyses of the distribution of marine nutrients.