The faster deepening of the phosphacline relative to the nitracline was correlated with ocean nitrogen fixation rates across Earth System Models (Fig. ). A differential deepening (i.e., residual TPO4) was quantified as the orthogonal distance from the TPO4 = TNO3 line. Across all three model scenarios, we found significant positive relationships between ocean nitrogen fixation rates and the residual TPO4 (Table ). The correlation coefficients and regression slopes also increased 5 with stronger emissions. This shows that the relationship between nitrogen fixation and declining phosphate-to-nitrate availability is dependent on the rate ocean warming and increasing stratification. Therefore, the CMIP6 model dynamics were consistent with the hypothesis that nitrogen fixation with stratification determines the faster deepening of the phosphacline relative to the nitracline.