On the seabed of Antarctica they are found well 332 canyons, deep up to 4000 m: to show its existence is one map recently published, the most detailed that has been created so far, with five times the number of canyons than previously identified. The map, together with the related catalogue, was drawn up by the University of Barcelona and the Irish University College Cork. Underwater canyons are not only spectacular structures that cut through the seabed, but also cover a important role in oceanic circulation and ice melting.
The underwater canyons of Antarctica
They have been identified around the world approximately 10,000 underwater canyonsalthough their number could be much higher since, so far, only 27% of the planet’s ocean floor has been mapped at high resolution. Compared to those present on the rest of the planet, Antarctic underwater canyons are larger and deeper due to the erosive action of enormous quantities of sediment transported by glaciers to the continental shelf: a slightly inclined surface, located below sea level, along which the emerged lands slope towards the oceans. On its margin the sediments accumulate, and then collapse on the steep slope which connects the continental shelf to the actual ocean floor.
By mixing with water, the debris creates a flow called “turbidity current”which with its speed, even 100 km/h, is capable of digging the canyons close to the escarpment. The most spectacular, long and branched, with U-shaped cross sections, are found in East Antarctica; in West Antarcticaon the other hand, are shorter and steeper, with V-shaped sections. The researchers hypothesize that this difference, which has never been highlighted until now, suggests a more ancient origin of the East Antarctic ice sheet.
There canyon map was created starting from Version 2 of the International Bathymetric Chart of the Southern Ocean (IBCSO v2), the most complete and detailed of the seabed in this area. The researchers used new, high-resolution bathymetric data and a new method to identify and analyze the canyons.
The role of Antarctic submarine canyons
Underwater canyons play a fundamental role because they transport sediments and nutrients from the coast towards greater depths, and constitute habitats that host a great biodiversity. They also allow the cold and dense water, present near the ice shelves, to flow towards greater depths, giving rise to the so-called Antarctic bottom waterfundamental for ocean circulation and capable of influencing the climate. Additionally, these canyons channel warmer waters, such as circumpolar deep watersfrom the open sea towards the coast. This mechanism is at the origin of the fusion of the base of the floating ice platformsessential for maintaining the stability of Antarctica’s internal glaciers. When shelves weaken or collapse, continental ice slides more rapidly seaward and contributes to raising its level.
