Seeds of doubt

Before the end of January, a company called Planktos plans to dump 50-100 tonnes of iron sulfate into a patch of ocean 100km wide in a bid to seed the growth of plankton - and so remove CO₂ from the air by photosynthesis.

The firm, based in California, US, and part-funded by Canadian rock star Neil Young, is only the latest in a series to try ’iron fertilization’. But its trial is the largest to date and comes at a time when questions are being raised about the value of the practice and its impact on the environment.

Iron - a nutrient required by phytoplankton for growth - catalyses nitrogen fixation and is in short-supply in some areas of the ocean. The theory is that iron added to the sea will spur the growth of phytoplankton and the resulting biomass will fall into the depths of the ocean - dragging down the CO₂ it has sequestered with it. What remains unclear is whether CO₂ captured in this way will stay underwater for very long.

’If the detritus does not sink deeply enough, it would be available through long term mixing in a relatively short time - years to decades,’ says Klaus Lackner, a professor of geophysics at Columbia University in the US. ’This could put the CO₂ back in circulation in the next 50 years - precisely when things are most critical.’

A recent study carried out by Michael Lutz, a marine scientist from the University of Miami in the US, also warns that the approach could be flawed. It shows that less carbon is transported to very deep waters during a summer bloom than in winter.¹

Planktos is not alone in exploring ocean fertilisation. Climos, another California-based company is investigating a similar approach. And Ocean Nourishment, as Australian firm, plans to use nitrogen-based fertiliser to achieve the same results. All hope to make money from carbon offsetting by trading credits on the international carbon market.

Changing seas

Meanwhile, after a meeting in November last year, the London Convention, which regulates activities such as the dumping of waste at sea, called for more research into ocean fertilisation before any commercial projects get underway.

’A big concern is that these operations may cause major alterations to ocean ecosystems and geochemical systems,’ Carol Turley from the Plymouth Marine Laboratory, UK told Chemistry World. ’We need to look at how these changes can be quantified accurately.’

Chris Vivian from the UK’s Centre for Environment, Fisheries & Aquaculture Science (Cefas) is chairman of the London Convention’s scientific advisory board. ’When these organisations take a vessel onto the high seas [which are open to all nations], they only require permission from the flag state overseeing that area,’ he told Chemistry World.

Climos has proposed an ethics code which calls for independent scientists to carry out ocean carbon experiments. In contrast, though the Planktos trial is not considered large-scale, the company’s approach is somewhat ’gung ho,’ Vivian said.

Planktos says it is a responsible member of the international ocean science community: ’Planktos’ plans have been so clearly and consistently stated as being composed of series of carefully planned and executed pilot scale projects.’

The firm’s research vessel, launched last month, is expected to deposit its load of iron sulphate at a ’secret location’ before the end of January.

Victoria Gill