THEY have been travelling through the depths of the North Atlantic, out of sight, out of mind, to better our understanding of climate change.

Now the remarkable work of underwater robotic gliders will be revealed in a wealth of oceanographic data collected during voyages on the waves and undersea currents spanning more than a year.

The 'Seaglider' robots have been used by the Oban-based Scottish Association for Marine Science (SAMS) to collect key information on how the seas are responding to rising global temperatures.

Capable of monitoring sea temperature, salinity, pressure and oxygen levels, the six-feet-long aquabots are released into the wild and operate on their own power, diving as deep as 330 feet.

Seven of the free-swimming probes were launched 18 months ago and have now gathered the equivalent of five years of data, which is being studied by scientists back on land.

The project's co-ordinators say that the milestone highlights a major change in how marine scientists collect information, as the Seagliders can spend months at sea without researchers even having to step on a boat.

And they are capable of travelling vast distances without direct human interference, with the group collectively covering more than 20,500 miles during their epic voyages.

Dr Stefan Gary, a research associate in physical oceanography at SAMS, said: “Seagliders allow oceanographers to make cost-effective, long-term, and long-distance observations, often in hard-to-access regions that ships rarely frequent and other ocean robots rarely go.

“Because of their durability we often deploy them in the winter, as they have been known to withstand extreme storm-force conditions.

“Seagliders also allow for very dense sampling of the ocean, collecting a profile every three kilometres, while a survey vessel usually samples every 10 to 30 kilometres.”

One of the Seagliders, dubbed 'Ardbeg', this week broke a SAMS distance record by completing a return trip of more than 2,100 miles along the Extended Ellett Line, a route from Scotland to Iceland that has been surveyed by scientists for 40 years.

Others have floated deep into the Atlantic, covering an era from the north coast of Ireland to Rockall, the most Westernly point in the British Isles, and north of Iceland. A separate deployment also surveyed the sea around the Shetland Isles.

As the Seagliders float along, they dive down into the depths towards the seabed and then rise to the surface, using fixed wings and a hydrodynamic shape to create a forward movement.

To submerge, a battery-powered pump moves oil into a pressurised container, increasing the density of the glider in the water and causing it to sink.

To bring the glider to the surface, oil is pumped back into a bladder to increase buoyancy. Live data is sent by the gliders via satellite to the pilots at SAMS, who can control and re-direct them remotely in near real-time from the Scottish Marine Robotics Facility, a command and control centre for Seaglider operations.

The project is the latest in a series of ocean-going endeavours led by the SAMS team involving their robots.

Earlier this month it was revealed that the will use custom-built seabots to explore the deepest parts of the ocean in a bid to discover how life can thrive in the inky blackness.

These extreme ocean regions, known as 'hadal zones', occur where one plate of the earth's geological crust is sliding underneath a neighbouring plate, forming deep trenches in the seafloor.

The Hades Project will see three purpose-built robots descending on three gouges in the bottom of the Pacific Ocean: the Atacama Trench off Chile (max depth five miles), Japan Trench south and east of Japan (5.9 miles) and Kermadec Trench north of New Zealand (6.24 miles).