D297: Geology & biology of the Portuguese canyons


 


About the cruise...

Cruise D297, aboard the RRS Discovery, will visit the Nazare submarine canyon offshore Portugal. Last summer our other ship, the RRS Charles Darwin, visited the area to take sediment cores through the mud at the bottom of the canyon. This year, the scientific team plan to continue their research here by towing a camera along the canyon floor to see what lives on the seabed. Based on what they see from the camera, they will then take samples of the seabed to look at the creatures in more detail.


Where are we going?

The cruise will be investigating the seabed just offshore Portugal. In particular, we will be looking at a huge submarine canyon called the Nazare Canyon. The ship will dock in Lisbon to pick up the scientific team and supplies, and will then sail out to the study area, where we will spend 3 weeks carrying out the scientific investigations.

The science carried out during this cruise will build on the results from last summer's cruise (CD157) to the area.


3D map of the cruise area
(Click to enlarge)

What are we investigating?


3D map showing the submarine canyons offshore Portugal. Click to enlarge.

The key objective of the cruise is to discover how sediment moves down the canyon. Many (but not all) submarine canyons around the world are directly associated with rivers, so they act as an escape chute for all the sediment discharged by the river. The Lisbon and Setubal canyons are linked to the Tagus River, and they channel sediment from the river down to the deep sea. However, the exact way in which this happens is unclear. The sediment may simply move smoothly and easily without interruption from the continental slope down the canyon and into the deep ocean basin. On the other hand, sediment may build up on the continental shelf and then cascade down the canyon in a series of small landlide events. These landslides may be caused either by the sheer weight of the sediment which has become unstable, or they may be triggered by earthquakes.

Find out more about the geology of the canyons
Find out more about sedimentary processes in the deep sea

Earthquakes are frequent along the Iberian margin, and can sometimes be very large. One such devastating earthquake occurred in Lisbon in 1755, and resulted in the death of thousands of people. Evidence of this earthquake can be seen in the layers of sediment on the ocean floor.

Find out more about the Lisbon earthquake.

To look at the geological processes operating in the canyon, we will be using specialised equipment. To take samples through the sediment on the seafloor we will use a piston corer and a box corer - this will make up the main part of the work we do on this cruise. However, in addition we will be using shallow seismics to look at the structure of the seabed, and a video camera to look at how the biology and geology are related.

The biologist on board will be using trawl nets to sample the life on the seafloor and walls of the canyon, and they will be looking out for clues to what controls the distribution of different species. Creatures living in such a dynamic environment need to be specially adapted to cope with sudden changes in their surroundings.


Research on board the cruise will be based on the information we collected with TOBI (Towed Ocean Bottom Instrument) last year. During the Classroom@Sea cruise, instruments to be used will include: SHRIMP, used for taking photographs and video of the seafloor and benthic biology; the piston corer and box corer which allow us to remove samples of sediment from the seabed; a shallow seismic surveying system which bounces soundwaves off the different layers of sediment below the seafloor to build up a picture of the sub-seafloor geology, and various biological sampling methods which will give us an idea of the ecosystems present in the canyons.

SHRIMP

Agassiz net used for biology sampling

TOBI


Find out more about...
The geology of the Portuguese canyons
How TOBI works and what sidescan sonar images look like
How we take sediment cores from the deep sea
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© Challenger Division for Seafloor Processes
October 2003
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