What are these ocean robots?

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A lot of the press coverage (such as the Daily Mail, Washington Post and the Japan Times) for the project in recent days has focussed on the ocean robots, or Seagliders, we will be deploying in the Bay of Bengal. So what are they, and how do they work?

UEA scientists preparing to deploy a Seaglider

Seagliders are about the size and weight of a small person, and look like a little yellow (or pink!) submarine. They are brightly coloured so that the field teams can spot them in rough seas and bad weather. They change their buoyancy much like a real submarine does, except that rather than filling tanks with air or water, they have a small bladder that they fill with oil (oil is lighter than water). They use their wings to turn vertical motion into horizontal motion, and can roll to turn, just like an aeroplane.

The salinity of the Bay of Bengal (g/kg). The water in the far north reaches values as low as 18 g/kg, around half the salt concentration of most of the world’s oceans!

Our ocean robots will dive from the surface to 1000m below the waves, every 3 hours for a month during the BoBBLE cruise. They will take measurements of how warm, salty and biologically active the water is every 50 cm, as well as how much mixing is occurring on scales of a few mm. These measurements enable us to understand how the ocean currents bring warm salty water from the Arabian Sea into the Bay of Bengal, where they mix with the much less salty water that comes from the outflow from the Ganges and other big rivers to the north. These different “water masses”, or bodies of water with different properties, form layers beneath the surface, and understanding how and when they mix will enable us to better understand how the ocean provides heat to the atmosphere, thus driving the Indian Monsoon.