British oceanographers say they have found evidence that phytoplankton growth in the north Atlantic is sharply limited by the availability of iron. The seagoing boffins suggest that their research could have important implications for efforts to fight climate change, as phytoplankton can absorb large amounts of CO2 from the atmosphere.
The new findings are based on measurements carried out in the central Iceland Basin by scientists from the UK's National Oceanography Centre (NOC) in the summer of 2007. The NOC boffins travelled aboard the Royal Research Ship Discovery, a British government scientific vessel.
The NOC scientists found very low levels of iron in the North Atlantic seawater, while other essential nutrients that would normally turn into phytoplankton remained unused. Adding small concentrations of dissolved iron to sample bottles taken from the sea resulted in more phytoplankton, more chlorophyll, and better photosynthesis - the sunlight-driven process by which plants remove carbon from the atmosphere.
"These results, backed up by additional experiments, are extremely exciting," says the NOC's Maria Nielsdottir.
"They provide strong evidence that low iron availability limits summer biological production in the high-latitude North Atlantic. This has only previously been suspected, but helps explain why the spring phytoplankton bloom does not continue well into the summer and why residual amounts of nitrate remain unused."
Some scientists have suggested that it would be possible to remove significant amounts of CO2 from the atmosphere by seeding suitable ocean regions with iron - the amounts of metal involved are small. This would allow the iron-starved, plant-like phytoplankton to increase in numbers to the full potential of their nutrient supplies, so aborbing massive amounts of carbon and presumably easing the greenhouse effect.
There has been a hotly-debated argument as to whether such efforts should qualify for valuable carbon credits under governmental schemes like those planned in the European Union. Critics of the idea say that the effects of such "geoengineering" are unproven, and that in any case the focus should be on humanity emitting less carbon rather than on sequestering it in the oceans afterwards.
Nielsdottir doesn't go as far as to say that iron-powered ocean sequestration is a good idea, but she does drop a hint.
"[This research] is important," she says, "because the high-latitude North Atlantic is second only to the Southern Ocean in its potential to lower atmospheric carbon dioxide and unused nitrate in the surface highlight the potential for even higher CO2 drawdown, high levels of which are an important cause of global climate warming."
Details on the resulting scholarly paper, Iron limitation of the postbloom phytoplankton communities in the Iceland Basin, can be found here. ®