Indian scientists recently carried out a controversial experiment in the ocean near Antarctica to get carbon dioxide captured from the air and stored in the sea. The experiment, meant to combat climate change, was a failure, but the scientists now say they learnt some valuable lessons.
The 75-day Indo-German experiment carried out amidst opposition from environmental groups has shown that dumping iron in the Southern Ocean does not help in capturing carbon dioxide (CO2) that is responsible for much of global warming.
"We are still analysing the data, but it seems to us that ocean fertilisation is not an attractive tool to combat climate change as originally thought," Satish Shetye, director of the Goa-based National Institute of Oceanography (NIO), told IANS.
Shetye however said that the experiment which concluded six weeks ago has given new insights on how the complex ocean ecosystems function. "We have learnt a lot irrespective of whether our original idea turned out to be right or not."
The results will be intensely discussed and prepared for joint publication in scientific journals at a workshop to be held in Goa by the end of the year, Wajih Naqvi of NIO, who was the leader of the expedition from the Indian side, told IANS.
The iron fertilisation experiment Lohafex - loha means iron in Hindi - was a joint venture of NIO and Germany's Alfred Wegener Institute for Polar and Marine Research and included some 40 scientists from five other countries.
It was to test the theory that adding iron to the waters would stimulate rapid growth of algae called phytoplankton that can suck up atmospheric CO2. Having taken up CO2, it was assumed that when they die, the algae will sink into the bottom of the ocean taking the carbon with it.
During Lohafex, scientists created a bloom of phytoplankton by fertilising an area of 300 square km with six tonnes of iron sulphate which dissolves in water. In two weeks the bloom's mass doubled by taking up CO2.
However, contrary to expectation, the bloom was quickly devoured by copepods, a group of small crustaceans. Even with further iron fertilisation the bloom stopped growing. As a result, only a small amount of CO2 was dispatched to the ocean floor.
The larger blooms stimulated by earlier experiments were due to a group of algae known as 'diatoms' which are protected against grazers by shells made of glass (silica). Diatoms could not grow in the Lohafex experiment because all the silicic acid (which the diatoms use for shell making) had already been extracted by previous, natural blooms. The result was that the beneficiaries of the iron were instead groups of algae called Phaeocystis, which are eaten by copepods.
Naqvi says that scientists are not sure if they know all the answers why productivity of phytoplankton is limited in that part of the ocean where they carried out the experiment. "I am willing to speculate the system is limited by something else," he told IANS.
He admits the potential of carbon sequestration in the Southern Ocean is smaller than originally thought. "We hoped we could remove one billion tonnes of CO2 annually. Now we think it is half of that."