Every so often a discovery is made that changes the beliefs that we hold about science. It has been generally accepted that the oxygen that is formed in the sea (as opposed to that which is dissolved from the atmosphere) all comes from the photosynthesis of marine plants. This of course can only take place relatively near the water's surface as sunlight does not penetrate to any great depths. Work by an international team led by Professor Andrew Sweetman at the Scottish Association for Marine Science has discovered what is termed as 'dark oxygen" which is being produced on the deep sea-bed between Hawaii and Mexico. The sea-bed is covered in potato sized modules which have been formed over millions of years when dissolved metals coat fragments of shells.

Nodules being extracted from the surface of the deep sea-bed. (Image from Science Photo Library NOAA in a BBC article)

What the team has shown (published this week in Nature Geoscience) is that these metal nodules act together as batteries to cause the electrolysis of sea-water to produce oxygen and hydrogen. The individual nodules produce a voltage of up to 0.95 V which is only slightly less than a typical AA battery and because they lie close together on the sea-bed they can act in series to electrolyse the sea-water where the minimum voltage required is 1.23 V (See Section 19 of the 2023 IB data booklet for the values for the two half-equations at 298.15 K).

Testing the voltage produced by the nodules collected from the sea-bed in the laboratory (Credit: Franz Geiger/Northwestern University).

These findings are important as several mining companies are developing the technology to bring the nodules to the surface and extract the metals from them. A petition which has already been signed by 827 marine science & policy experts from over 44 countries has been formed to stop the deep-sea mining of metals until its full effects can be determined, as there is a danger that it could severely and possibly irreversibly damage deep-sea life which is dependent upon this 'dark oxygen'.