Why do the oceans matter in mitigating climate change? Can the oceans capture carbon dioxide emissions without affecting life below water? JENNET ORAYEVA is our guide.
As the largest ecosystem on the planet, the world’s oceans are a pillar of climate regulation and a powerful source of solutions to the changing climate. The theme of this year’s World Oceans Day – ‘life and livelihoods’ – focuses on the importance of sustaining the ocean for all forms of life on Earth. Through the use of nuclear and isotopic techniques to reveal the changes in the ocean, the IAEA supports coastal countries in better understanding these vital ecosystems, so that they can protect them and sustain their local economies that depend on the ocean.
The rise of atmospheric greenhouse gases, particularly carbon dioxide from industrial activities and anthropogenic land use have been the dominant contributors to global warming. The ocean plays a major role in buffering the earth’s climate system and in reducing the rate of global warming: acting as a giant sink, it captures and stores CO2 away from the atmosphere.
Understanding Carbon Cycle and the Role of ‘Blue Carbon’
The IAEA joins hands with the leading experts from all over the world to study organically absorbed carbon, known as Blue Carbon, captured and stored especially by coastal ecosystems, such as seagrass meadows, mangrove forests and tidal marshes to understand the natural mechanisms of organic carbon sequestration and catalyse sustainable solutions to the problem of climate change and corresponding ocean degradation.
These ecosystems are very efficient in accumulating and storing large quantities of organic carbon in both plants and the sediment below. They absorb and store carbon at a much faster rate than other ecosystems such as forests.
Despite being much smaller in area and body mass than that of terrestrial forest ecosystems, their global carbon sequestration potential is comparable. Seagrass meadows cover less than 0.2 per cent of the ocean floor, but accumulate about 10 per cent of the carbon buried in the oceans each year, mostly in underlying sediments. Mangrove soils have a tremendous capacity to accumulate and retain carbon stocks over millennia. Understanding the sequestration of organic carbon in these ecosystems will help clarifying how the ocean is coping with human-made CO2 emissions and what its absorption capacity is.
The ocean has already absorbed a quarter of global CO2 emitted into the atmosphere over the last century, but most of this CO2 has not made it to the coastal vegetated ecosystems that can absorb it. Mainly accumulated on the surface of the ocean, these greenhouse gases therefore make the water more acidic and hostile to fragile marine life such as coral reefs and shellfish. The increasing level of the surface water acidity, known as ocean acidification, has emphasized the need to better understand the ocean’s capacity to cope with CO2 emissions.
In-depth knowledge on carbon sequestration can help expand the natural carbon sinks in coastal ecosystems to absorb CO2 entering the ocean and thus reducing the surface water acidity and store CO2.
“Coastal Blue Carbon constitutes an important component of nature-based solutions that are providing to be essential to offset the negative impacts of climate change,” says Director of the IAEA Environment Laboratories, Florence Descroix-Comanducci. “However, when these ecosystems become damaged or disrupted by human activities, their capacity to sequester carbon can be compromised. As these ecosystems degrade, an enormous amount of carbon that has been accumulated for thousands of years can potentially be released as CO2 , further exacerbating climate change.”
Recognition of the important role of these unique ecosystems has been growing in the past decade, but there is still a need for more scientific research and data to aid policymaking, she added.
IAEA projects on Blue Carbon
IAEA scientists collaborate with a wide range of research institutions to assess carbon sequestration rates in coastal environments using nuclear techniques, such as the 210Pb dating.
“While a number of studies have been conducted during the last decade, many questions remain open such as the evaluation of global hotspots that are understudied like seagrass and mangrove forests along the Brazilian and Asian coastline,” said Research Scientist at the IAEA Radioecology Laboratory, Pere Masque Barri.
Natural and anthropogenic carbon accumulation in sediment at millennial scale can be determined using the 14C technique, while estimates in timescales of decades or centuries can be achieved using other radionuclides that are present in the environment, such as 210Pb and 137Cs and Pu isotopes. This provides a timeframe of carbon sequestration and its variation with time due to natural or human impacts.
These radionuclide-based techniques provide a unique assessment of whether natural or anthropogenic disturbances may have caused losses of carbon, for instance via sediment resuspension and erosion processes. 234Th and 210Po are also widely used by IAEA scientists for carbon cycle research to assess the efficiency of the process that transports carbon from the upper ocean to depth via sinking of particulate matter. The use of short-lived radionuclides such as 228Th and 7Be that can also be used as tracers of sedimentation dynamics to obtain accurate results at timescales of weeks, months, or even a few years.
The IAEA is involved in Blue Carbon projects in Australia, Brazil, Denmark, France, India, Myanmar, New Zealand, Sweden, Tanzania and the United States. It is also engaged in an innovative project coordinated by Oceans 2050 to assess the carbon sequestration capacity of seaweed farms across the world. National and regional IAEA technical cooperation projects are being developed to assess the importance of carbon sequestration in aquatic systems for nature-based climate change adaptation strategies, environmental conservation, and socio-economic benefits. Work is under way to establish regional capacities for assessing carbon sequestration in aquatic systems in Africa.
- Orayeva is of the IAEA Department of Nuclear Sciences and Applications.