Nutricline depths in CMIP6 were quantified similar to the cruise observations. For each model grid point, we linearly interpolated nutrient concentrations for every 1 dbar of pressure up to 1000 years) for five repeated cycles (305 years in total), using a modified version of the CESM2-MARBL ecosystem (67). We ran a control run after the 305-year initialization, where historical emissions continued for another 61 years. For experimental runs, we tested how nitrogen fixation rates and nutricline depths responded to changing DFe either increasing globally, in just the northern hemisphere, or in just the southern hemisphere. We augmented DFe in these areas by either 25%, 50%, or 100%. Each experimental run started immediately after the 305-year initialization and lasted for 61 years as well. Therefore, a total of 9 experimental runs were conducted to constrain how DFe affects nitrogen fixation rates and nutricline trends in CESM2. For this analysis, nutrient concentrations were converted to µmol kg -1 and nutricline depths were quantified using the same method as the CMIP6 models.