Fertilizing the Oceans
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Most people don't think about but plants - whether on land or in the sea, absorb Carbon Dioxide or CO2. That's a good thing because CO2 is one of the greenhouse gases that's causing the earth's surface to warm up. Hi, I'm Bryan Yeaton and this is the Weather Notebook.

Some oceans - even with an abundance of plant life, aren't aborbing a lot of CO2. The vast Southern Ocean around Antarctica is one of them. As correspondent Allan Coukell reports, scientists there are trying to boost the ocean intake of the gas.

The oceans are home to billions of tiny one-celled plants called phytoplankton. Phytoplankton, like all plants, need nitrogen and phosphorous to grow. But the Southern Ocean around Antarctica has low concentrations of phytoplankton, even though these nutrients are plentiful. One possible reason is the scarcity of another nutrient: iron. A lack of iron might restrict the gorwth of phytoplankton, thereby limiting the amount of carbon dioxide that the plants can remove from the atmosphere. Rob Murdoch is with New Zealand's National Institute of Water and Atmosphere. He was part of a group of scientists that sailed to the Southern Ocean to dump a solution of iron into the waves.

We went down to the southern ocean in our research vessel Tangaroa, and effectively fertilised an area of about 50 square kilomtres with about 2 tonnes of iron. We mixed iron sulfate into sea water and then released that from the stern of the ship through a pipe and into the surrounding ocean.

Ed Abraham is another NIWA oceanographer. He looked at satellite images of the phytoplankton growth after the experiment, and he was surprised by what he saw:

The amount of iron that we added at the beginning of our experiment was 2 tonnes, which you can fit on the back of a small truck. It's not very much at all. And the volume of water that's got more phytoplankton in it that we see in the satellite images amounts to around 20 million olympic-size swimming pools. So you take your small truckload of iron, you put it into 20 million swimming pools and you get ten times the iron concentration that you had previously.

Understanding the growth of phytoplankton is important for our understanding of climate. But the scientists empahsise that the experiment is not a potential antidote to global warming. Even fertilising the entire ocean would not be enough offset human production of carbon dioxide.

That's correspondent Allan Coukell of Auckland, New Zealand. The Weather Notebook is a production of the Mount Washington Observatory