The ‘seeding of the oceans’ with iron as a ‘quick fix’ to climate change has been the subject of much debate over recent years, with some companies going as far as commercialising the selling the concept in exchange for carbon credits. The idea – to seed the surface of the oceans with iron (a trace element essential to photosynthesis that is often a limiting factor in the marine world) in order to stimulate phytoplankton growth, in turn sequestering carbon dioxide from the atmosphere – isn’t entirely new. Over thirteen research groups have trialled iron fertilisation since 1993 to varying degrees of success, although most of these projects have fallen short of the dream of the late oceanographer John Martin back in the late 80’s: “Give me a half a tanker of iron and I will give you another ice age”

After a series of moderate succeses onver the past decade, it seems that the idea of sequestering CO2 in the oceans might truely be dead and buried. Project LOHAFEX, a joint Indo-German group, succeeded in seeding an area of 300km2 with over 6 tonnes of iron, resulting in a doubling of plankton biomass in just two weeks. What the team didn’t factor was the power of the oceans food web. Instead of the plankton bloom undergoing a natural death and sinking to the ocean floor (along with the sequestered CO2), the phytoplankton became an instant food source for hungry copepods, who in turn were consumed by a swarm of larger crustaceans (amphipods – see inset picture).

This ‘grazing effect’ was apparently absent from previous experiments, which instead  stimulated the growth of diatoms. Diatoms differ from most phytoplankton in that they are protected from being eaten by protective shells made of silica. Whilst the experiment did succeed in providing new insights into the dynamics and ecology of plankton, to quote Ken Caldiera “I think we are seeing the last gasps of ocean iron fertilisation as a carbon storage strategy”.