The iron stimulates plankton growth, which 'binds' carbon dioxide out of the atmosphere - getting rid of one of the gases which warms Earth's atmosphere.
A trial, called Eifex, has been hailed a success, after a bloom of plankton sank 1,000 metres below the ocean, taking with it carbon dioxide.
So how will this affect plankton feeding animals and fish? They just have to adapt to new depths really quick as well as a new iron rich diet.
What could possibly go wrong?