DAVID GREEN reports on a new piece of technology which will help give us a better understanding of what is happening in our seas

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THE QUAYSIDE is a hive of activity as equipment is off-loaded and replaced on deck and the ship re-fuelled ready to embark the next day.

Among the scientists returning to Lowestoft on the 3,000 tonne, 73-metre long research vessel Endeavour is a group which, for the first time, has been using a torpedo-shaped marine glider to sample oxygen levels in the North Sea.

There is mounting evidence that oxygen levels are declining, especially in the bottom layers of the sea, and if the trend continues, the future of fish 
and shellfish stocks will be endangered. Climate change 
may be at least partly to 
blame.

Investigations, using other devices for detecting oxygen levels as well as the sea glider, are being spearheaded by the Lowestoft-based Centre for Environment, Fisheries and Aquaculture Science (CEFAS) in collaboration with the University of East Anglia (UEA).

On the busy quayside I meet Liam Fernand who is leading the research project and who has just spent more than two weeks aboard the Endeavour during a five-week voyage to all areas of the North Sea.

The voyage was essentially to monitor fish stocks, one of a series of regular CEFAS trips aimed at assessing the state of fisheries, but space and time was found for the oxygen survey.

I wait with Liam and members of his team as the sea glider – encased in a protective box – is lifted down by crane on to the quayside.

When the lid is lifted the glider – nicknamed Orca - looks simple enough. But it is in fact a very complex piece of technology with the ability to be satellite controlled and to change its density to order so that it floats back up to the surface.

“It has no propulsion and therefore glides through the ocean changing its buoyancy to move up and down through the water column,” Liam said.

The sea glider made 90 dives at locations throughout the North Sea during its five-week trial.

Data it collects is returned via satellite and is processed by a team which includes Bastien Quest, a 24-year-old PhD student at the UEA, who has previously helped test the glider in the Antarctic and in the Atlantic.

Liam, 42, who lives in Lowestoft with his wife and three children, said: “Over recent years we’ve discovered that oxygen concentrations – important to all marine life – are reducing.

“This is due to two reasons, one of them a rise in temperature. As sea water warms it has less capability to contain dissolved oxygen. There definitely seems to be a link with climate change.”

The other reason for the lack of oxygen is the decay of nutrients, particularly in the bottom layers of the sea.

Scientists are lucky to have data about oxygen levels in the North Sea dating back to 1902.

“Because it has got so many countries around it, the North Sea is one of the most intensively studied of the world’s seas,” Liam said.

Oxygen levels actually increased in the North Sea during the 1970s. This is thought to be largely the result of European Union legislation which led to a reduction in the volume of nutrients entering the sea, mainly from farm fertilizers, although most nutrients in deep water areas derive from the Atlantic, via the Gulf Stream.

However, that increase in oxygen levels was short-lived and it has continued to decline.

“The decrease has been more pronounced in the last ten to 15 years or so. The central and north part of the sea stratifies so you get a sharp temperature difference. Bottom waters can be as cold as seven degrees and the surface waters can be up at 18 degrees. That difference can occur even over a small difference in depth, sometimes only five metres,” Liam said.

Plankton, the creatures at the bottom of the marine food chain, reproduce in sunlight and produce oxygen via photosynthesis so an oxygen rich layer develops near the surface of the sea.

But as they die and decay oxygen levels are depleted in the lower levels of the sea where many of the plants and fish – cod, haddock and other “bottom dwellers” – are found.

“Oxygen depletion is now on the edge of affecting fishery production and if it continues it will cause problems,” Liam said.

If investigations show the problem is man-made then action might be possible, even if it takes years to have an effect.

“If action is necessary it needs to be taken before the problem occurs. If you wait until you’ve got problems then it will be too late,” Liam added.

n The CEFAS ground fish survey has been running in one form or another since 1966. It is carried out annually in a co-ordinated manner with five other North Sea boundary countries in the third quarter of the year.

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