Credit: ALFRED-WEGENER-INST.

Preliminary results from a controversial Indo–German ocean fertilization experiment (LOHAFEX) have cast doubt on whether stimulating algal growth can help the sea sequester substantial amounts of carbon dioxide.

Earlier this year, researchers aboard the German research vessel Polarstern (pictured) poured 20 tonnes of iron sulphate over a 300-square-kilometre area of the Southern Ocean around the Antarctic (see Nature 457, 243; 2009).

However, grazing by small crustaceans prevented blooms from growing as much as some had hoped, according to Germany's Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, one of the experiment's backers. Furthermore, a lack of silicic acid in the water restricted the growth of diatom plankton, which are more resistant to predation than the algae. The fertilization therefore removed only a "modest amount" of carbon from the environment.