A brand-new study led by researchers from Durham University and the National Oceanography Centre (NOC) has shown for the first time that a massive underwater landslide dam is stopping megatons of organic carbon from getting to deep-sea ecosystems.
One of the biggest canyons on Earth, the Congo Canyon carries sediment, oxygen, nutrients, pollutants, and organic material from the Congo River and the coasts to the deep sea. Submarine canyons are enormous, but remarkably little is known about them. Scientists can use satellite images to track changes in river channels, but they can’t do the same for submarine canyons because the water is too deep.
Scientists used seafloor mapping data from the Congo Canyon-Channel, which was collected between 2005 and 2019, to close this knowledge gap by examining how the canyon had changed and evolved.
Sand and mud flows that frequently occur along the canyon-channel, behaving like snow avalanches on land, transport matter from shallow to deep water. In this instance, scientists found that a massive underwater landslide had collapsed into the Congo Canyon and blocked it. This landslide was comparable in size to the largest landslide dams ever recorded on land. The obstruction caused a 150 m-thick accumulation of sediments containing 5 megatons of organic carbon in the canyon axis by stopping the flow of material into deeper water. This amazing discovery will change the ecosystems of the deep sea, which depend on the movement of organic matter through the submarine channels.
According to co-author and NOC Leader of Marine Geosystems Research Dr. Mike Clare, “Such landslide dams have never been observed in a deep-sea canyon, though they have been reported from rivers. To put things in perspective, the sediment trapped by the underwater dam was almost four times as much as the sediment flux that leaves the Congo River each year. There has never been a record of this important event before.
