Phytoplankton growth in the Indian Ocean is limited by nitrogen and phosphorus in the north and by iron in the south.
Increasing anthropogenic atmospheric deposition of nitrogen and dissolved iron (dFe) into the ocean can thus lead to significant responses from the Indian Ocean ecosystems.
Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of the Fe cycling.
This study uses a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale.
The model includes three major dFe sources and represents an internal Fe cycling modulated by scavenging, desorption, and complexation with multiple, spatially varying ligand classes.
Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe input stimulates diatom in the southern Indian Ocean poleward of 50S and the southeastern tropics.
However, diatom decreases in the southern Arabian Sea due to the phosphorus limitation, and diatom is outcompeted there by coccolithophores and picoplankton, which have a lower phosphorus demand.
These changes in diatom and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake poleward of 50 S and the southeastern tropics while decreasing it in the Arabian Sea.
Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition.