Among the CMIP6 models, CESM2 had the highest ocean nitrogen fixation rates as well as the highest residual TPO4. Although higher than most, this model was consistent with the convergent estimate of ocean nitrogen fixation quantified by Wang et al. (2019) (36). Finally, CESM2 showed 15 nutricline trends that were the most consistent with observations. Hence, we next investigated different processes in CESM2 that may affect nitracline and phosphacline trends. phosphate requirement led to reduced upper ocean phosphate demand by 2100 (37). We analyzed these same experiments and found that flexible phosphate uptake also led to shallower phosphacline depths (Fig. ) (37). However, flexible phosphate uptake did not have a major effect Submitted Manuscript: Confidential Template revised November 2023 16 on nutricline trends through time (Fig. ). Therefore, flexible nutrient uptake stoichiometry impacted the initial depths of nutriclines, but was not a factor for the long-term trends.