Science & Environment

Seabed test mimics carbon dioxide release

Undersea gas release
The experiment will monitor any impact of CO2 release on life and sediments

Scientists are beginning a month-long experiment in Scottish waters to study the impact of a possible leak from an undersea carbon dioxide storage site.

Working in Ardmucknish Bay near Oban, researchers will allow CO2 to bubble through sediments from a buried pipe and look for impacts on marine life.

Capturing CO2 from power stations and burying it under the seabed is viewed as an important global warming fix.

A number of countries have plants in operation, though the UK does not.

This is believed to be the first time that an impact of CO2 escape on seabed ecosystems has been investigated.

"We want to study what happens if there is a leak from a carbon capture and storage (CCS) reservoir - or more likely, from a fault in a pipe or at the injection site," said Henrik Stahl from the Scottish Marine Institute in Oban, who is in charge of the project.

"We'll study how this affects the ecosystem, the animals and microbes living in the sediments, and how the CO2 transforms in its passage through the upper layers of the sediment," he told BBC News.

Injection was due to begin on Monday, but late delivery of a part meant a postponement. It is now due to begin on Wednesday.

Acid test

The scientists will release 80-800kg of CO2 per day from a pipe buried about 10m down in sediment.

Locator

They anticipate it will change the acidity of seawater in the immediate area from its current value of about pH 8.2 down as low as pH 6.5.

Studies in places where CO2 bubbles into the ocean naturally from vents on the sides of underwater volcanoes show that over long periods, this can substantially change the ecosystem.

Snails and coral cannot make shells; seagrasses take over.

But these sites are not reliable indicators of what would happen during a release from a CCS site. They tend to be in warmer waters, and the release is constant for many centuries, possibly longer.

Ideally the UK team would like to do tests nearer potential North Sea CCS sites. But these lie in far deeper water much further from the coast, rendering it prohibitively expensive.

The research team, which involves staff from Plymouth Marine Laboratory, the National Oceanography Centre and other UK institutions, will monitor polychaete worms, sea urchins and molluscs living in the bay's sediments.

They will be able to curb the release if they detect any serious impact.

Oil rigs
Carbon capture and storage could make use of the UK's existing network of oil and gas rigs

They will also collect data that can be used to refine computer models of how CO2 spreads and disperses in sediment and water, and evaluate various bits of monitoring kit.

"It's not only about perturbing the system, but also studying how we can study it - how we detect and study a leak using state-of-the-art sensors," said Dr Stahl.

A number of reports conclude that fitting coal- and gas-fired power stations with CCS ought to be as important as renewables in curbing greenhouse gas emissions.

But economic and political issues have impeded the take-up of the technology.

The UK has the best resources of any European country in terms of offshore storage capacity, but development of the industry has been curtailed by lack of consistent government support.

SSE and Shell are among companies bidding for £1bn of UK government funding to build the nation's first CCS plant. Their bid would see CO2 extracted from flue gas produced by SSE's Peterhead gas-fired power station and pumped under the seabed via Shell's Goldeneye offshore platform.

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