Sediments on the seabed store large amounts of organic carbon. "The natural reservoirs of organic carbon in the continental shelf sediments must be better protected to prevent increased greenhouse gas emissions," a group of researchers states.
The legally binding climate agreement reached in Paris in 2015, the Paris Agreement, states that the global average temperature must not increase by more than 2°C, and preferably not exceed 1.5°C, compared to pre-industrial levels. This requires drastic emission reductions and the removal of CO2 from the atmosphere.
Carbon is life
“A certain reduction in CO2 emissions can be achieved by nature itself if ecosystems that remove significant amounts of carbon from the atmosphere are better protected, managed, and restored”, says researcher Markus Diesing at the Geological Survey of Norway (NGU).
Together with four NGU researchers and a Swiss colleague, the findings are now published in a scientific article in the journal Communications Earth & Environment.
Without carbon, there is no life. Carbon is the central element in the molecules that make up living beings. Carbon compounds are also important in fuels.
Increased CO2 emissions
"We have mapped the amount of organic carbon stored in sediments on the Norwegian continental shelf and examined how quickly the stores are replenished," says Diesing.
"We found that the top ten centimeters alone store 814 million metric tons of organic carbon, and that seabed sediments are filled with six million tons per year. This corresponds to 22 million tons of CO2-equivalents per year, or about 45 percent of Norway's emissions.”
Almost half of the annual accumulation occurs in deep trenches on the shelf, depressions carved into the shelf by ice streams during the ice ages. The area that stores the largest amount of organic carbon in seabed sediments is found in the eastern part of the Norwegian Trench.
If the sediments are disturbed and stirred up, for example by bottom trawling, the result could be increased CO2 emissions into the water column and possibly into the atmosphere.
"The processes behind this are so far poorly understood. We want to better understand the impact human activities have on the amount of CO2 released from the seabed. We will use our maps together with data from fishing activities to get a better understanding," says Diesing.
MAREANO data
A significant portion of the data in this research comes from 20 years of geochemical data collection in the MAREANO mapping program, which is operated by the Norwegian Mapping Authority and the Institute of Marine Research in collaboration with the Geological Survey of Norway (NGU). Most of the work done has also been funded by the MAREANO program.
So far, international attention has been focused on the preservation and restoration of coastal ecosystems, including mangrove forests, kelp forests, and seagrass meadows, to keep carbon in place.
“Our findings show that marine seabed sediments store more carbon than coastal ecosystems in Norway. The government has highlighted seabed sediments as a nature-based climate solution in its management plans for Norwegian marine areas, and our results provide a basis for better analyses in the management of marine areas”, says NGU researcher Markus Diesing.
Reference: Diesing, Markus, Paradis, Sarah, Jensen, Henning, Thorsnes, Terje, Bjarnadóttir, Lilja Rún, Knies, Jochen (2024). Glacial troughs as centres of organic carbon accumulation on the Norwegian continental margin. Communications Earth & Environment 5, 327.