Canyon discovered

"Like a river under water!"
Marine researchers from Bremen discover giant canyon off the coast of northwest Africa

Scientists from the Research Center Ocean Margins in Bremen made a sensational discovery during their latest expedition on board RV "Meteor" which ended only a few days ago. Off the coast of Mauritania they came across an enormous under-water canyon in a phantastic shape. It meanders a distance of more than 200 kilometres from the shallow coast until way out towards the Atlantic deep-sea. The scientists could follow the deep gorge in the sea floor to water depths of more than 3,000 meters. The leader of the expedition, Prof. Horst Schulz, is sure that "the canyon plays a central role in transporting sediment from the continental slope to the deep-sea".

The scientists named the Canyon "Cape Timiris Canyon" after a nearby coastal feature. It was discovered right at the beginning of the expedition at about 19 degrees latitude north and came as a big surprise: "Even the most recent maps showed only large expanses of level seafloor where we found the canyon," Prof. Schulz reported. In an on the spot decision the geoscientist from Bremen changed the research program in order to map the canyon. A good week later, the picture was almost complete.

"In many respects the 'Cape Timiris Canyon' is reminiscent of the Rhine river" says Horst Schulz. At the foot of the continental slope, at a water depth of 3.000 meters the African continent gives way to the deep-sea. Here the canyon is two to three kilometres wide and cuts about 300 meters deep into its environment. Similar to the rivers Rhine or Mosel, the canyon features many meanders (see attached figure). These switchbacks are part of the evolution of such a canyon, which up to now has not been understood very well.

Seismic investigations of the deep subsurface show that the canyon - like the Rhine river - has been stationary for at least ten million years. On images of the seafloor the scientists from the Research Center in Bremen could recognize amazing details in addition to the meanders: old cut-off arms, diverse branching points, changes from steeper to more level areas of the canyon, as well as levees at the rim of the canyon. Also, the overall length is comparable to the Rhine river. Apart form the over 200 kilometers, which were investigated, there are at least 500 to 600 additional kilometers, (linear distance) towards the deep-sea.

The on board investigations suggest that in the past large quantities of seafloor deposits along the continental slope were mobilized and transported into the deep-sea. The 'Cape Timiris Canyon' apparently played a key role in these transport processes. Sediment cores of about ten meters in length, which were stamped out of the seafloor using a large hollow cylinder with a diameter of 12 centimeters, support this assumption. They show that time and again so-called turbidity currents - a mixture of water and sediment - flowed towards the deep-sea. In one of the cores the scientists distinguished 33 different sediment rich turbidity currents in only 9 meters of core. At intervals of only a few years, the currents rolled through the canyon.

"Actually, it is hard to believe, that such large unknown objects can still be found on our planet" resumes Prof. Horst Schulz. "We are already excited to see the results of further analysis of the material from this expedition".



Further information:
Albert Gerdes
DFG Research Center Ocean Margins
at the University of Bremen
- Public Relations -
Fon: +49-421-218-7761
mail:
www.oceanmargins.de