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<p>Although the northern Indian Ocean (IO) is globally one of the most productive regions and receives dissolved iron (<span class="inline-formula">DFe</span>) from multiple sources, there is no comprehensive understanding of how these different sources of <span class="inline-formula">DFe</span> can impact upper-ocean biogeochemical dynamics. Using an Earth system model with an ocean biogeochemistry component, this study shows that atmospheric deposition is the most important source of <span class="inline-formula">DFe</span> to the upper 100 <span class="inline-formula">m</span> of the northern IO, contributing more than 50 % of the annual <span class="inline-formula">DFe</span> concentration. Sedimentary sources are locally important in the vicinity of the continental shelves and over the southern tropical IO, away from high atmospheric depositions. While atmospheric depositions contribute more than 10 % (35 %) to 0–100 <span class="inline-formula">m</span> (surface-level) chlorophyll concentrations over large parts of the northern IO, sedimentary sources have a similar contribution to chlorophyll concentrations over the southern tropical IO. Such increases in chlorophyll are primarily driven by an increase in diatom population over most of the northern IO. The regions that are susceptible to chlorophyll enhancement following external <span class="inline-formula">DFe</span> additions are where low levels of background <span class="inline-formula">DFe</span> and high background nitrate-to-iron values are observed. Analysis of the <span class="inline-formula">DFe</span> budget over selected biophysical regimes over the northern IO points to vertical mixing as the most important mechanism for <span class="inline-formula">DFe</span> supply, while the importance of advection (horizontal and vertical) varies seasonally. Apart from removal of surface <span class="inline-formula">DFe</span> by phytoplankton uptake, the subsurface balance between <span class="inline-formula">DFe</span> scavenging and regeneration is crucial in replenishing the <span class="inline-formula">DFe</span> pool to be made available to the surface layer by physical processes.</p>