By Anita Lombardo
Oceans are among the oldest carbon sinks on the planet: 6 tonnes of greenhouse gases are absorbed yearly by each square kilometre of water. What is problematic is that, according to the Intergovernmental Panel on Climate Change (IPCC), the expected carbon emissions that each person will be adding into the atmosphere every day by 2100 is also around 6 tonnes. How can oceans continue to deliver their century-old climate regulation services with anthropogenic emissions rising this fast?
Scientists have proposed a geoengineering technique known as ocean fertilisation, which consists of injecting iron in specific areas of the oceans to accelerate carbon uptake. Marine phytoplankton and algae indeed rely on this mineral to carry out their photosynthetic activity, and absorb carbon while doing so. Dissolving significant quantities of iron in low photosynthetic areas could thus boost the growth of these organisms, that once dead sink all the way to the seafloor, locking away the stored carbon.
“Oceans are among the oldest carbon sinks on the planet”
Image of a phytoplakton (left), which form the foundation of many ocean food chains, by the National Oceanic and Atmospheric Administration (NOAA) and aerial photo of a phytoplankton swirl (right) around Gotland, a Swedish island, by the United States Geological Survey (USGS).
Supporters of iron fertilisation highlight the potential contribution of this technology to mitigate climate change, as large amounts of carbon dioxide are locked at the bottom of the ocean at accelerated rates.
Nevertheless, the potential side-effects of iron fertilisation remain largely unexplored. Many scientists express concern on the unintended consequences of the human manipulation of oceanic nutrients and are sceptical over its real benefits for climate mitigation: "The main issue with iron fertilisation seems to be – leaving aside the potentially fundamental but poorly constrained impacts that this activity has on the ecosystem – that not much of the sequestered carbon dioxide actually makes it into the seafloor” states Dr Christian Maerz, associate professor in Biogeochemistry at the University of Leeds. Although phytoplankton and algae sequester carbon dioxide, part of their sediments is degraded in the top layers of the ocean or eaten up by other marine organisms, thus releasing that carbon back into the atmosphere. The amount of CO2 that is effectively stored at the bottom of the ocean is thus difficult to detect, and the impact artificial fertilisation would have on this amount is similarly hard to predict.
“Scientists express concern on the unintended consequences of the human manipulation of oceanic nutrients”
Studies are still trying to determine for how long will carbon remain stocked on the seafloor. Oceanographer Anand Gnanadesikan and colleagues at Princeton University in New Jersey have predicted that anywhere between 2 and 44 per cent of the carbon delivered to the deep ocean by fertilisation could be returned to the atmosphere within a century.
Although urging for a cautious intervention in the deeply interconnected and sensitive marine ecosystems, some scientists see iron fertilisation as a valid scientific pursuit: “There’s no basic science that is useless if it’s good science, if it increases your understanding of what you’re studying,” says Viktor Smetacek, marine biologist who has supervised three fertilisation experiments in the Artic currents. “And it’s the same with these iron fertilisation experiments. We’re learning about how pelagic ecosystems – the plankton – how they function.” This technology could thus help scientists gain a better understanding of natural nutrient cycle processes and their importance for marine ecosystems.
Therefore, many questions still remain open concerning the benefits of this controversial technology. In any case, its existence demonstrates well that scientific knowledge and technological development are working together in order to find feasible solutions to the environmental challenges that humanity is currently facing.