About the cruise...


The Portuguese Margin cruise is the key cruise for the Classroom@Sea project, when our two teachers, Elena and Ian, will be joining the scientific team aboard RRS Charles Darwin (left). During the cruise we will be investigating the geology and biology of the submarine canyons located offshore Portugal, using a variety of scientific techniques including sediment coring, seafloor imaging using sonar, seafloor videos, biological sampling and seismic surveying. This work is being carried out as part of a large EC-funded research programme called EUROSTRATAFORM which involves scientists from all over Europe.

Where are we going?

The cruise will be investigating the seabed just offshore Portugal. In particular, we will be looking at the processes affecting a huge submarine canyon called the Lisbon/Setubal 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 17 days carrying out the scientific investigations.

The science carried out during this cruise will use the results from an earlier cruise (scheduled for November 2003) to target areas that look particularly interesting. This earlier cruise is being carried out by SOC scientists on board a Dutch research vessel called RV Pelagia, which is owned and operated by the Royal Netherlands Institute for Sea Research (NIOZ). The team on board Pelagia will carry out a survey of the seafloor in the work area using an instrument called TOBI (Towed Ocean Bottom Instrument). TOBI uses sound waves to build up a picture of the shape of the seafloor.


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 landlisdes 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 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 biologists 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 around the results from a previous cruise which will use TOBI (Towed Ocean Bottom Instrument), to image the seafloor surface using sonar. 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.


Net used for biology trawling


TOBI


SHRIMP


© Challenger Division for Seafloor Processes
August 2003
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