World Oceans Day: Harnessing the Power of ‘Blue Carbon’ in Mitigating Climate Change

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% of the ocean floor, but accumulate about 10% 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 Florence Descroix-Comanducci, Director of the IAEA Environment Laboratories. “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 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 Pere Masque Barri, Research Scientist at the IAEA Radioecology Laboratory.

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.