The cruise observations suggest that phosphacline depths deepened by approximately 20 m over the past 5 decades, a rate that is almost an order of magnitude larger than most CMIP6 predictions for the historical period (Fig. , Tables and). At the observed rate, nutrient availability throughout the southern oligotrophic gyres may soon resemble the western side of the North Pacific subtropical gyre (Fig. and Table ). This transition is possible due to the predicted 20 decrease in iron stress for nitrogen fixation in this region . In turn, nutrient availability at the western side of the North Pacific subtropical gyre may soon resemble the North Atlantic subtropical gyre with widespread phosphorus stress (Fig. and Table ). A trend towards more phosphorus stress possibly driven by nitrogen fixation has already been observed in this area (41, 42). Therefore, the current patterns and trends in nutricline depths provide a basis for predicting which regions will begin to show increasing phosphorus stress for marine productivity.