The first, biologically unclear results were published last year in the journal Nature Geoscience. They arrived from several expeditions to the deep-sea area between Hawaii and Mexico, where Professor Sweetman and his colleagues sent sensors to the sea floor – to a depth of about 5 km (3.1 miles).
This area is part of a large area of seafloor covered with natural metallic nodules that form when seawater-soluble metals collect on fragments of shells or other debris. It is a process that takes millions of years.
The sensors the team deployed repeatedly indicated that oxygen levels were rising.
“I just ignored it,” Professor Sweetman told BBC News at the time, “because I was taught that oxygen was only produced through photosynthesis.”
Eventually, he and his colleagues stopped ignoring their testimony and instead decided to understand what was going on. Experiments in their lab – with the nodules the team collected submerged in beakers of seawater – led the scientists to conclude that the metal lumps were creating oxygen from seawater. They discovered that the nodules generate electrical currents that can split (or electrolyze) seawater molecules into hydrogen and oxygen.
Then there was a backlash in the form of rebuttals posted online by scientists and seabed companies.
One critic, Michael Clarke of the Metals Company, a Canadian deepwater mining company, told BBC News that the criticism focused on “the lack of scientific rigor in the design of the experiments and the collection of data”. Essentially, he and other critics argued that there was no oxygen generation – only bubbles produced by the equipment during sample collection.
“We have ruled out that possibility,” replied Professor Sweetman. “But these (new) experiments will serve as proof.”
This may sound like a niche technical argument, but several multi-billion dollar mining companies are already exploring the possibility of extracting tons of these metals from the seabed.
The natural deposits they are targeting contain metals vital to making batteries, and demand for these metals is growing rapidly as many economies switch from fossil fuels to, for example, electric cars.
The race to extract these resources has raised concerns among environmental groups and researchers. More than 900 marine scientists from 44 countries signed the petition, external highlighting environmental risks and calling for a moratorium on mining.
Speaking about his team’s latest research mission at a press conference on Friday, Professor Sweetman said: “Before we do anything, we need to – as best we can – understand the (deep-sea) ecosystem.
“I think the right decision would be to wait before we decide whether it’s the right thing to do as a global society.”
