Deep-sea asphalt mounds found off West African coast
Scientists have discovered a large area of the deep seabed strewn with mounds of asphalt off the coast of Angola, hosting rich animal life.
This is the first such discovery in the Atlantic proper or in the Southern Hemisphere, and the first time the creatures living around them have been studied in detail. It arises from a long-term collaboration between energy company BP and scientists at NERC's National Oceanography Centre (NOC).
The researchers found at least 21 kinds of deep-water creature living around the tarry structures, including octopuses, blobfish, sea stars and coral-like sea fans. 'It seems to be a very rich animal community - the asphalt provides a hard surface for them to attach themselves to, so animals like sponges can get a foothold,' says Dr Daniel Jones of NOC, the study's lead author.
He adds that these rare habitats may turn out to be important for how animals are distributed across the ocean floor, perhaps as stepping-stones that allow species to move into new areas and enable genetic material to flow across widely-dispersed populations.
BP experts first noticed the structures while searching the seabed for signs of energy deposits with the potential for exploitation. The asphalt mounds identified cover 3.7 square kilometres and sit around 2km beneath the surface. Closer investigation with remotely-operated subs revealed more than 2,000 mounds. Some are just inches from side to side; others are hundreds of metres across.
The BP staff alerted researchers at NOC, with whom they have a long-standing collaboration. The scientists examined the geological data and the images from BP's robots in an effort to understand the variety of living things around these structures, and their wider importance for marine biodiversity.
The mounds form when heavy, tarry hydrocarbons ooze up from beneath the sea floor and harden into asphalt much like the stuff that's used to surface roads. Only a handful of other examples are known, and those only since 2004, when a much larger 'tar volcano' came to light in the Gulf of Mexico. They are related to cold seeps - best known as places on the seabed where lighter hydrocarbons like methane leak into the water - in fact, both kinds of undersea fluid flow are found at the Angola site, leading the scientists to suspect that different parts of the same flow of hydrocarbons are somehow being separated on the journey up to the seafloor, with the lighter part emerging as a cold seep and the heavier forming asphalt mounds.
The study appears in Deep Sea Research 1 and is open access.
This story is republished courtesy of Planet Earth online, a free, companion website to the award-winning magazine Planet Earth published and funded by the Natural Environment Research Council (NERC).