Iron Hypothesis

The Iron Hypothesis was formulated by oceanographer John Martin, based on theories by Joseph Hart and first tested in 1993. In 1988, Nature published the results of Martin's experiments as well as his speculations on climate change. It was hoped that fertilizing the oceans with iron would draw down atmospheric CO₂.

Certain areas of the oceans have high levels of plant nutrients, such as nitrates and phosphates. However, the phytoplankton does not grow as strongly as it should, given the plentiful supply of sunlight and nutrients. John Martin argued that the lack of micronutrients, trace metals and particularly iron, was a limiting factor for growth of phytoplankton in HNLC (High Nitrate, Low Chlorophyll) ocean surface waters. Ken Johnson, Dick Barber and Kenneth Coale of the Moss Landing Marine Laboratories in Monterey Bay, California, were able to prove John Martin was correct, in a series of tests conducted near the Galápagos Islands in 1993 and again in 1995, with results published in Nature. By seeding or fertilizing the surface layer of the sea with fine particulates of iron, growth blooms of phytoplankton could be encouraged.