The history of the ocean seabed could be central to the future health of planet Earth, say scientists.
Seabeds capture carbon from the remains of marine life. But when the ocean floors are disturbed by trawling or coastal development, the carbon is released from the sea into the atmosphere, contributing to global warming.
Scientists also believe that the seabed’s ability to capture carbon could be used to cut global CO2 emissions by up to 6 per cent of the amount needed to cap the rise in global temperatures at 1.5ºC.
Carbon stores have been mapped around the world, but scientists are hoping they can go deeper to understand with greater accuracy the human and animal behaviours that cause seabeds to release or capture the gas.
“We will write a new history of the ocean, telling the story of how the seabed has been changed over centuries by human activities,” said Professor Callum Roberts, a marine biologist who is leading the Convex Seascape Survey at the University of Exeter.
“We're figuring out where are the most, the deepest and the most rich deposits of carbon in the seas,” he said, of the project which also involves the Blue Marine Foundation, a UK charity.
“At the moment, we don't have really strong science to give us robust answers,” he told The National. “We're recreating the oceanography back to 17,000 years ago and we can turn back the clock.”
The comprehensive survey, which also brings in researchers from the King Abdullah University of Science and Technology in Jeddah among other institutions, could alter how coastal seas are managed and protected.
“When we think about marine protection, we protect certain things like habitats or species, but not typically the sediments and the organic matter and carbon that’s contained within (them),” said Zoe Roseby, a marine geologist at the University of Exeter who is part of the five-year project.
Shallow seabeds of the Gulf
Although most the research has taken place in the UK, the findings will be of relevance to the Arabian Gulf, a shallow sea where urban development and commercial shipping increase at a rapid pace.
“We’re focused on continental shelves, the underwater extensions of land masses. They go down to about 200 metres, which means the entirety of the Arabian Gulf is continental shelf,” said Prof Roberts, who has written about coral reefs in Saudi Arabia, which he helped to map in the 1990s.
Although most fishing in the Gulf does not disturb the seabed, the increase in trawling, and the need to create deeper sea routes for commercial shipping could put the area at risk.
“We need to understand that impact, at least because we would need to incorporate this international carbon budgets, so that decision makers know that it's happening and they know that they need to include this in net zero calculations,” he said.
Studies had shown there were benefits and negative side-effects to energy infrastructure such as offshore oil wells and wind farms.
But Prof Roberts also suggests that shallow sea-beds could be disturbed so as to move the carbon to the deep sea, where there is little chance of it escaping into the atmosphere.
“If you're stirring up carbon from the seabed, then if there is a flow of water off the shelf, then that carbon could be taken into the deep sea, which is a long-term carbon store,” he said.
Little is known about this process, and it is one of the possibilities that the project hopes to find an answer to.
“If some of that carbon is going down into the deep sea, then disturbance could actually contribute to long term storage. It’s a paradox that we don’t know scientifically what the answer is,” he said.
Prof Roberts believes the Gulf could be a good test case for this because of the interaction between the freshwater Euphrates and Tigris rivers that feed into the sea, and the sea water from coming in from the other side through the Straits of Hormuz.
“That's one of the things that's keeping the Arabian Gulf habitable for marine life, is that you get this big exchange of water coming in,” Prof Roberts said.
“It could be that disturbing carbon in the Arabian Gulf is leading to the transport of that carbon through the Strait of Hormuz into the Arabian Sea and deep water,” he said.
“There is possibly a way in which that carbon could be transported to somewhere it is more secure and less likely to come back into the atmosphere,” he said.
Antarctica samples go to Jeddah
The research is already expanding to other parts of the world.
A recent expedition to Antarctica, led marine ecologist Professor Carlos Duarte who is based at KAUST, will seek to establish the role that whales play in maintaining the ocean's ability to sequester carbon.
The survey looking back 500 years will examine the changes in carbon stores in periods when whales thrived on the peninsula, compared to those when whale hunting led to their near extinction.
"We hope to either validate or reject the hypothesis that great whales contribute to carbon sequestration by keeping the ecosystem in a highly productive stage," Prof Duarte told The National.
The samples extracted earlier this year will arrive in Jeddah in June month for eDNA testing.
"If the hypothesis is correct, then when whales were being hunted down, we expect to see that ... the organic carbon content of the sediment will decline, ... along with the decline in productivity in plants," he said.
"We can reconstruct a record of how the Antarctic ecosystem responded to the massive depletion of whales," he said.
North west coastal research
Scientists are finding the richest carbon stores around the UK and Ireland by looking at deep history all the way back to the end of the last Ice Age.
The melting of ice sheets 17,000 years ago changed the shape of the coastline, as well as the tidal currents.
A team led by Dr Sophie Ward developed a model that could trace the changes in coastal shapes, and tidal currents through this time, in order to identify the places with the most carbon-rich mud stores, and how vulnerable they are to disturbance.
“We've used this case study to look at the carbon stock of the surface elements of that area, to consider the amount of carbon that's being stored in this elements, but also the kind of quality, the reactivity of that carbon as well," Dr Roseby said.
"So, how vulnerable is that carbon to disturbance from human pressures, such as trawling."
The study published last month found that while mud was still accumulating in places like the Western Irish Sea Mud Belt and the Celtic Deep, in the North Sea’s Fladen Ground above Scotland, the mud floor was ancient, formed after the end of the last Ice Age and preserved for millennia by low tidal currents.
She hopes the model will allow them to predict the location of muds in other lesser studied seas, such as those on the coast of Patagonia, where the team will be heading next.
Their findings will remain open source so that other scientists can access them, she said.
The data that we produce in our projects is going to be open access, so other members of the scientific community will be able to utilise our model and data outputs for like, any you know, ongoing work that they're doing,” she said.
Sedimentologist Torsa Sengupta showed how she was able to trace the amount of carbon in a muddle samples from the laboratories at Exeter University's Penryn campus in Cornwall.
Sediment cores several metres long were extracted from the North Sea corers, then cut into metre-long samples and analysed in laboratories.
The deeper the sediment, the older the carbon deposits in there will be. The mud is first dried and then mortared make a fine powder. Then an acid is poured onto it to remove the inorganic carbon that comes from sea shells.
The resulting powder, which has isolated the organic carbon, is then put into a carbon analysis machine.
“We use this course to identify the total amount of carbon, and the difference in the proportion between organic and inorganic carbon, and how did the amount and the types of organic carbon change through time,” she said.
“This is mainly to find out the natural organic carbon, or the natural carbon reservoirs deep down in ocean sediments which can spread,” she said.
The research can take months of this painstaking work. Yet Ms Sengupta said she is compelled to do it because of the rise in climate-related migration, which affects the developing world the most.
“Even when humans had no control over the climate, the natural climate has driven large human populations to migrate,” she said.
“Huge ocean sediments, are the natural stores of carbon, and so we if we don't disturb it, we would not release more carbon,”
“That motivated me to find out, where is this total source of carbon?”.
