Pouring iron powder into ocean to fight global warming

A team of Indian and German scientists have started a 70-day ocean expedition to find out if pouring iron powder into ocean can trap greenhouse gas, CO2 from atmosphere and can keep it long enough under water to make a difference in global warming situation, according to a report by Times of India.
The scientists leaving from Cape Town, South Africa in a research ship towards a region in Antarctica plan to pour 20 tonnes of iron powder in an ocean area of approximately 300 sq km.
The idea is to stimulate a rapid blooming of phytoplankton, a microscopic algae that grows on the ocean surface.
Like all plants, phytoplankton sucks up CO2 from air and converts it to carbon-based compounds like carbohydrates.
The plant quickly dies and starts sinking, taking the carbon with it.
The team plans to observe if the dead plant sinks down enough in the ocean to make the process scientifically viable.