The world's oceans are home to different habitats that capture and store carbon—known as "blue carbon." These include habitats that are typically found along coastlines, such as salt marshes and seagrasses, as well as vast seabed sediments further offshore made of mud, silt and sand. The extent to which these habitats are protected and, where possible, restored, could have huge implications for the world's future climate.

Until now, there was limited coordination of information about how much carbon is stored in UK marine habitats, especially in seabed sediments. But a new report from the Blue Carbon Mapping Project, published today, provides a new baseline for the UK's blue carbon. In fact, the UK is the first nation to map and estimate the amount of carbon stored in all of its seabed habitats and this milestone could influence marine policy both here and around the world.

The Blue Carbon Mapping Project, completed by the Scottish Association for Marine Science on behalf of World Wildlife Fund, The Wildlife Trusts and the RSPB, gives the UK an opportunity to show the rest of the world just how important blue carbon is and why we need to protect it. Helping nature to recover on land and at sea is fundamental for tackling climate change, alongside reductions in emissions.

My colleagues and I reviewed and collated existing data about blue carbon habitats and carbon in seabed sediment to create new estimates of the size of and rates of accumulation in the carbon stores in UK seas. We found that seabed sediments are the largest blue carbon store, holding an estimated 244 million tons of organic carbon. Most (98.3%) of this carbon is stored within the top 10cm of these sediments.

Coastal vegetated habitats, although covering only 1% of the UK's marine area, contribute significantly to carbon storage, accounting for 1.7% of the UK seas' total organic carbon stores. Salt marshes are the largest of these, containing 60% of the organic carbon in coastal vegetated habitats. Mostly found in England and Wales, salt marshes are powerful carbon sinks due to the rich, organic soils they contain. Seagrass beds, though less extensive, also play a critical role, but our report calls for improved mapping to better understand their distribution and capacity.

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