The UK’s seabed is more valuable as a carbon sink absorbing pollution from industry than as a source of oil and natural gas, estimates from the Office for National Statistics show.
The findings put the value of Britain’s marine “natural capital assets” at £211 billion ($291bn) and represent an emerging area of research where nations try to put a value on the environment.
The estimates also investigate the benefits for the UK from “blue carbon", or the amount of greenhouse gases captured by the ocean and coastal ecosystems.
It is part of a global effort to put financial costs on using fossil fuels.
Its advocates say this will help policy makers to focus on reducing harmful emissions.
Using conservative estimates, the UK's statistics office said sea grasses, mud, sand and salt marshes already capture at least 10.5 million tonnes of carbon dioxide equivalent a year, with a value of £57.5bn.
By comparison, woodlands in the UK captured carbon worth about £55bn.
Because blue-carbon data is still uncertain, the agency used the lowest range figure to estimate the value.
The real value could be six times higher, with the seabed storing the equivalent of more than 60 million tonnes a year.
That value is also expected to grow in coming years after the UK government set out plans to artificially remove pollution from industry and pump it under the seabed to help reach a goal of generating net-zero emissions by 2050.
The value the sea generates in absorbing carbon from the atmosphere is higher than what is earned from producing oil and natural gas, or from fishing, the UK data showed.
It is second only to the income generated from having beaches for recreation, as the economies of dozens of towns near the sea rely on tourism.
Renewables are catching up, with more wind farms being installed offshore.
The value of marine renewable energy production grew by 37 times in the decade since 2008, when the offshore wind industry barely existed, the UK agency said.