We presented evidence for a deepening of the phosphacline that is decoupled from any commensurate change in the nitracline. However, there are caveats to be considered. First, we restricted our global trend analysis to nutricline depths that were deeper than 50 m and from 45°S -45°N. Omitting depths shallower than 50 m did not appreciably affect the observed trends, as they remained consistent when including depths deeper than 25 m (Tables and). The applied latitudinal range removed the Arctic Ocean from our analyses, despite this region experiencing some degree of nitrogen limitation (38). However, the sampling density in the Arctic was too low to quantify trends from nutricline depths that met our criteria. Furthermore, the Arctic experiences high variability in sea-ice cover, which is a major driver of stratification absent from the rest of the oligotrophic ocean (39). Second, there were notably less cruise observations from the earliest 5 and latest years, but we still found a significantly faster deepening of the phosphacline from 1982 -2012 (Tables and). Third, ocean basins were sampled at different frequencies leading to less statistical power for some basins, most notably for the Indian Ocean. However, the nitrate and phosphate depth profiles were mostly sampled concurrently throughout time and space; thus, the sampling variability is not expected to have any effect on the differences in the trends observed 10 for the two nutrients (Fig. ). Fourth, although the global trends were robust, we recognize that variability in the phosphacline trends were more influenced by measurement error than the nitracline trends. Accounting for these caveats, we still find significant evidence for declining phosphate-to-nitrate availability over the past 5 decades .