D297: Geology & biology of the Portuguese canyons


 


About the cruise...

Cruise D297, aboard the RRS Discovery (left), will visit the vast submarine canyon system offshore Portugal. Last summer our other research vessel, the RRS Charles Darwin, visited the area to take sediment cores through the mud at the bottom of the canyons on cruise CD157. This year, the scientific team plan to continue the research here by investigating the biology of the canyons, as well as the geological process active in this area. They will begin 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 a range of different samples of the seabed to look at the creatures in more detail. This research is being carried out as part of a new EC-funded research programme called HERMES, which is investigating how different ecosystems on the seafloor around Europe work in relation to their surrounding environment.


Where are we going?

The cruise will be investigating the seabed just offshore Portugal. In particular, we will be looking at two huge submarine canyons known as the Nazare Canyon and the Setubal Canyon (right). The ship will dock in Lisbon for a couple of days to pick up the scientific team and supplies, and will then sail out to the study area on 27th July 2005, where we will spend 3 weeks carrying out the scientific investigations. A lot of the work will take place in the upper part of the canyon (the part closest to the coast), but we also plan to do research in the deeper parts.

The scientific team on board is composed of scientists and research students from several different universities and institutions around Europe - to find out who's on the team, visit the Who's Who page.


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 science carried out during this cruise will build on the results from last summer's cruise (CD157) to the area. Last year, we were interested in finding out more about the shape of the canyons and how sediment moves down the canyon from the continental shelf towards the deep sea. To do this we surveyed the area with sidescan sonar and multibeam bathymetry, and then took samples of the layers of the mud on the canyon floor using a sediment corer. This year, our research will be slightly different - now that we have a better idea of how sediment moves around in the canyon, we want to see how this affects the type and numbers of creatures living there. This not only includes animals like fish and plankton, but also benthic creatures who live on the canyon walls and floor.

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

Submarine canyons are important for moving sediment down from the continental shelf to the deep sea. Along with this sediment is a large quantity of organic material, which provides nutrients and food for marine animals. Because of the constant supply of sediment and food, submarine canyons are often found to be teeming with life. As well as providing safe habitats for many creatures that actually live on the canyon floor and walls, canyons can also provide safe havens for young fish and sea mammals. It is important for us to be able to understand how these canyon ecosystems work and how they are affected by changes in the environment - for example, if an underwater sediment landslide occurred in the canyon, would this catastrophically wipe out some of the ecosystems, or are they adapted to coping with such events? An important part of our research into canyons is understanding how they affect the dispersal of pollution. If canyons are very good at transporting sediment down to the deep sea, then they will also funnel pollutants very efficiently, which could have dramatic consequences for deep sea ecosystems.

The first part of the cruise will be spent using an instrument called TOBI (Towed Ocean Bottom Instrument), which uses sound waves to build up an image of the seafloor. These images can be interpreted by the scientists on board to see what the seafloor is made of and what features exist down there. The data we collect during this exercise will be added to the data we collected last year from further down the canyon.

When the TOBI survey is finished, the biological sampling will start. We will use a special underwater camera called SHRIMP to look at the floor and walls of the canyon to see what is living there. An instrument known as Bathysnap will be lowered to the seafloor, where it will take pictures of the seafloor environment over the course of the cruise. We will take samples using a number of different types of equipment such as coring instruments to sample the mud from the seafloor surface, trawling nets and dredging equipment. In addition, we will be using traps to catch small creatures such as amphipods.

The team from Oceanlab Aberdeen will be using a piece of equipment called a lander - a metal frame onto which special instruments can be mounted to monitor the seafloor environment. The landers are weighted so that they sink to the seafloor, where they wait for a signal from the ship that tells them when to drop the weights and float back to the surface when the monitoring period has finished. In this case, the lander will be equipped with a special digital camera which can operate in water depths of up to 6000 metres - that's the length of 50 football pitches! The camera is baited with mackerel, a particularly smelly fish, which will attract scavenging fish - fish that will basically eat anything! The camera will take pictures once every minute, and the pictures allow the team to get lots of information including which fish come to the bait, how long they stay, how many there are, and their size. Once the pictures are downloaded from the camera, it will be Nikki's job to go through all the pictures one by one, identifying the fish, measuring and counting them. Nikki never knows what she's going to come across in the next picture, and often there are big surprises like huge sharks and really weird fish!

TOBI

SHRIMP

Agassiz net used for
biology sampling

The ROBIO lander

The megacorer

So, we have a lot of work to do in just 3 weeks! The scientific team on board RRS Discovery is a mix of geology and biology scientists and students from around Europe, along with a team of engineers and technicians who look after the equipment and makes sure it works properly - click here to find out who's who on the scientific team.



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
June 2005
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