Whale poo could be the key to promoting plant growth in the Southern Ocean as a rich source of iron and essential for plankton, according to experts. The only problem is, there is not enough.

PhD candidate at the University of Tasmania, Lavenia Ratnarajah, said her research showed that whale poo significantly added to the ocean's iron content.

"Their poo contains over 10 million times higher iron concentrations than sea water and the population has diminished tremendously over the last century or so," Mr Ratnarajah told 936 ABC Hobart.

"That’s a massive decline in iron that’s going into the water naturally," she said.

Other sources of iron in the oceans included continental coastlines, underwater volcanoes, glaciers and melting sea ice, but it was not enough.

"Turns out [whale] poo is really important. It's really nutritious and it can potentially act as a fertiliser, so we can get more plant growth with whale poop," she said.

When referring to plants, Ms Ratnarajah was talking about marine plankton in the ocean, which was vital to a large amount of marine life.

Whale poo contains 10 million times the amount of iron compared to seawater. ( Supplied: Micheline Jenner, Centre for Whale Research )

"They’re these little organisms that are kind of like the rainforest of the ocean and they’re very important because it’s the base of the marine food chain, so they feed everything along the line.

"They also produce over half of the world’s oxygen, so every second breath you take comes from the ocean," she said.

For now while the other sources of iron remained positive, Ms Ratnarajah said the amount they provided was like a drop in an Olympic-sized pool.

"There’s not enough for the entire Southern Ocean and large areas are really far from all these sources, so the amount of iron in the water is really low," she said.

The other aspect was that whales have the ability to spread their poo throughout the ocean unlike other sources, which were constrained to particular areas.

"As they swim, they poop and all the poo rises to the surface and it’s what we call a buoyant slurry, so it disperses along the top of the water," she said.

The poo then sank into the ocean and diluted with the water to add the nutrients needed for plant life to thrive.

The migration period for whales also played its part by naturally spreading iron through the great distances covered by the mammals.

Ms Ratnarajah said, although her work was important, she often faced smirks and strange looks after explaining her research to others.

"Everyone laughs when I tell them what I’m doing my PhD on, but it does bring a really important way for me to get into a conversation about climate change and the importance of it," she said.

The research can be found via the University of Tasmania on the Conversation website.