Importance of multiple sources of iron for the upper-ocean biogeochemistry over the northern Indian Ocean

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