Anthropogenic iron deposition alters the ecosystem and carbon balance of
the Indian Ocean over a centennial timescale
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
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.