New Scientist 
Feb 11, 2013
GEOENGINEERING is being tested – albeit inadvertently – in the north Pacific. Soot from oil-burning ships is dumping about 1000 tonnes of soluble iron per year across 6 million square kilometres of ocean, new research has revealed.
Fertilising the world’s oceans with iron has been controversially proposed as a way of sucking carbon dioxide out of the atmosphere to curb global warming. Some geoengineers claim releasing iron into the sea will stimulate plankton blooms, which absorb carbon, but ocean processes are complex and difficult to monitor in tests.
“Experiments suggest you change the population of algae, causing a shift from fish-dominated to jellyfish-dominated ecosystems,” says Alex Baker of the University of East Anglia, UK. Such concerns led the UN Convention on Biological Diversity  (CBD) to impose a moratorium on geoengineering experiments in 2010.
The annual ship deposition is much larger, if less concentrated, than the iron released in field tests  carried out before the moratorium was in place. Yet because ship emissions are not intended to alter ocean chemistry, they do not violate the moratorium , says Jim Thomas of the ETC Group, a think tank that consults for the CBD. “If you intentionally drove oil-burning ships back and forth as a geoengineering experiment, that would contravene it.”