Multiplying the ocean's CO2 guzzlers

Adding nutrients to areas of the ocean that lack phytoplankton is one way of reversing the effects of global warming explored by a new BBC TV documentary, Five Ways To Save The World.

Five Ways To Save The World Monday 19 February 2007 2100 GMT on BBC Two

Our oceans are teeming with phytoplankton: millions of microscopic plants beneath the waves that are vital to the marine ecosystem because they form the base of the marine food chain.

Phytoplankton are not visible to the naked eye but from space, satellite images show that phytoplankton form enormous green swirls hundreds of kilometres long around coastal waters.

They employ photosynthesis, using sunlight and carbon dioxide (CO2) from sea water, to sustain themselves.

"Just like trees, they can take carbon dioxide and give us back oxygen," says Professor Ian Jones, an ocean engineer from the University of Sydney, Australia.

When the plankton die, they sink deep to the ocean floor, taking the carbon with them.

What Professor Jones wants to do is add one of the components of urine - urea - to the areas of the ocean that lack phytoplankton.

Urea is a nitrogen-rich fertiliser that helps plants grow and therefore by adding it to the parts of the ocean that lack phytoplankton, Professor Jones thinks it will turn these areas into a lush "forest", eventually reversing the effects of global warming.

'Desolate Zone'

It was a natural disaster - flooding - that was to trigger his idea to introduce nutrients to the ocean. When rivers burst their banks and flood agricultural land, the fertiliser or nutrients on the land are washed away into the sea.

If you do not like the outcome, you can turn off the tap Professor Ian Jones

And by studying the effects of rainfall in Sydney harbour, he discovered that when it rained, more nutrients come into the harbour and the phytoplankton numbers increase.

When the rain goes, they decrease again.

In 1995, a team of US oceanographers set out to study the "Desolate Zone" - an area 400km (250 miles) to the south west of the Galapagos Islands, where there are few plankton.

The researchers wanted to test the theory that this area was missing one vital nutrient: iron.

Half a tonne of iron was added to the sea. As a result, plankton bloomed and the ocean turned green.

By the end of the experiment, the scientists had calculated that the small area of newly fertilised phytoplankton had absorbed an additional 7,000 tonnes of CO2, the equivalent of 2,000 fully grown trees.

Liquid nitrogen

But for Professor Jones, there was a problem with iron fertilisation. Eighty percent of the ocean does not react to it because there is already enough, especially around the coast.

Urea would be pumped into the ocean from a nitrogen factory

The challenge for him was to find a source of nutrients that would be easily and cheaply available.

Like iron, nitrogen is one of the nutrients that makes plankton grow, but it has to be in a form that the marine organisms can process.

Professor Jones' solution is to use granular urea - bitter-tasting white granules - and convert it into liquid form so that it can go through a pipeline into the ocean.

The plan would be to run the pipe from a nitrogen factory and pump gallons of urea into the ocean to feed the plankton.

Unknown consequences

Adding large doses of nutrients to the ocean, however, does not always have a beneficial effect.

If there are too many plankton, when they die they drive bacteria production that results in a depletion of oxygen in the water and the death of other marine life.

The urea plan would only work in areas where there is not much plankton to begin with, says the professor.

"The important thing about ocean nourishment is that we are not doing it where there is lots of productivity; we are doing it in the desert regions of the ocean," he explains.

"If you do not like the outcome, you can turn off the tap. It's like irrigation. When you turn off the food supply for the plankton, they will just die."

But then there is the issue of meddling with ecosystems that have found a natural balance over millions of years of evolution.

Even Professor Jones admits: "Once you start managing nature you have to continue to manage nature, there is no use hoping that it will restore itself to a new equilibrium set up by humans."