Fertilization trades-off with other areas.

If scientists were to widely fertilize the Southern Ocean or any other iron-depleted waters with iron, the effort would temporarily stimulate phytoplankton to grow and take up all the macronutrients available in that region. But eventually there would be no macronutrients left to circulate to other regions like the North Atlantic, which depends on these macronutrients, along with iron from dust deposits, for phytoplankton growth. The net result would be an eventual decrease in phytoplankton in the North Atlantic and no significant increase in carbon dioxide draw-down globally.

Lauderdale points out there may also be other unintended effects to fertilizing the Southern Ocean with iron.

“We have to consider the whole ocean as this interconnected system,” says Lauderdale, who adds that if phytoplankton in the North Atlantic were to plummet, so too would all the marine life on up the food chain that depends on the microscopic organisms.

“Something like 75 percent of production north of the Southern Ocean is fueled by nutrients from the Southern Ocean, and the northern oceans are where most fisheries are and where many ecosystem benefits for people occur,” Lauderdale says. “Before we dump loads of iron and draw down nutrients in the Southern Ocean, we should consider unintended consequences downstream that potentially make the environmental situation a lot worse.”