Nearly a billion tonnes of buried carbon discovered off Norway’s coast

Norway’s seas play a far larger role in removing carbon from the atmosphere than previously thought, a new study shows. The data suggest that seabeds off the country’s coast bury six million tonnes of carbon every year, equivalent to around 45% of the carbon in the greenhouse gas carbon dioxide that Norway emits every year. The scientists warn that activities such as bottom trawling, which disturb the seafloor, could release some of this stored 'blue' carbon and damage natural processes that reduce the amount of greenhouse gases that reach the atmosphere.

“We have long known that coastal vegetation, such as kelp beds, seagrass meadows and salt marshes, remove carbon dioxide from the atmosphere,” said the senior author of the study, Dr Markus Diesing from the Geological Survey of Norway in Trondheim. “However, those areas are tiny compared to the seabed stretching across the entire so-called continental margin. We found that the seabed locks away nearly a hundred times as much carbon as seagrass meadows and salt marshes do.”

Billions of tiny plants and animals in the ocean continuously remove carbon from the surrounding environment. When they die, their bodies sink to the bottom of the sea and are buried in seafloor sediments. Ultimately, this permanently locks away the carbon in their bodies, preventing carbon dioxide from entering the atmosphere and further accelerating climate change.

“Most of the organic carbon gets remineralised to inorganic carbon on the way to the seafloor and even in the upper parts of the seafloor remineralisation continues,” Dr Diesing explained.

“We also discovered that some areas of the seabed, including the Skagerrak and troughs in the sea floor that were scoured out by glaciers during ice ages, lock away far more carbon than others,” said Dr Jochen Knies from the iC3 polar research hub in Tromsø. “Protecting these areas from bottom trawling could help to preserve the ocean’s ability to slow down the pace of climate change.”

The research team used over 1,500 individual observations to calculate the amount of carbon being removed by seafloor burial. As expected, they found that coastal seagrass meadows and salt marshes are much faster at removing carbon. However, because deeper areas cover a vastly larger area, they remove far more carbon overall.

In total, the team estimates that 814 million tonnes of carbon are currently locked away in Nordic continental margin sediments, of which 320 million tonnes are stored in glacial troughs. This compares to just 9 million tonnes that have been locked away by seagrass meadows and salt marshes combined.

The study “Glacial troughs as centres of organic carbon accumulation on the Norwegian continental margin” has been published in the journal Communications Earth & Environment.