BBC News By David Shukman image captionApollo II is a prototype deep sea mining machine. It was tested off the coast of southern Spain in 2019 A long-running dispute over plans to start mining the ocean floor has suddenly flared up. For years it was only environmental groups that objected to the idea of digging up metals from the deep sea. But now BMW, Volvo, Google and Samsung are lending their weight to calls for a moratorium on the proposals. The move has been criticised by companies behind the deep sea mining plans, who say the practice is more sustainable in the ocean than on land.