Topics

Join us!

If you enjoy writing about science, then join our team of student writers to get your work published on our site!

Apply!

Difficulties in the Deep Blue

By Laura Hooper

Photo credit: [8]

Did you know that we actually know more about the surface of the Moon and Mars than Earth’s ocean floor? [1]. This seems unbelievable, that we better understand features on another planet than our own. In fact, even though the entire floor has been mapped it’s only to a resolution of 5km, and less than 0.05% has been mapped in enough detail to detect small features [1]. It is due to the fact that this remote environment is not easy to access or measure that we have such difficulty in mapping it. The majority of the ocean floor actually rests on the ocean crust which is between 4,000 and 6,000 metres deep! Therefore the study of this environment requires very specialist equipment and skills, and is called bathymetry [2].

The ocean depths have been an area of interest and curiosity for humanity for many years now. Captain James Cook led voyages between 1768 and 1780, taking observations of ocean depth, water temperature and wind speed. These voyages are the first exploration, study and mapping of oceans. As time passed technological advances allowed more and more expeditions to be completed and valuable data to be collected. This includes ‘The Challenger’, (1872-1876). This was the first voyage that set sail with the sole purpose of studying the oceans. They sailed around the world observing water temperatures at the surface and different depths and taking samples of the sea sediments [3]. Data collected from expeditions like this helped generate the first sea floor map in 1959, but there is still much more to discover, and difficulties to overcome, but our quest to do this is aided by the huge advances in technology and equipment:

T.O.B.I

This stands for a towed, ocean, bottom, instrument. Ships tow them from a tether and the instrument uses scan sonar, (sound), to view the ocean floor from the sides and the bottom. This technology has been in use since 1990. They use their scanners to form detailed images of the ocean floor that can be used to create a map of its topography (shape). The only disadvantage to this method is that it is limited in range and speed by its tethering to a ship [4]. See below a short video of a T.O.B.I being launched [5].

Autosubs

These are robot submarines and unlike T.O.B.I’s they aren’t limited by a pilot or a tether. Instead on-board computers can be programmed with instructions prior to launch and the submarine can then follow these for the duration of the expedition. Because of this they have been used in Arctic and Antarctic missions since 1999 as they can operate under the sea ice and glaciers. However one problem with these machines is powering them, as due to the lack of oxygen a combustion engine cannot be used. Therefore they are reliant on battery power, so to conserve power and increase studying time they travel incredibly slowly [6].

Both of these machines are used to map the ocean floor. Another method that can be used is seismic surveys, these pick up the release of any air bubbles that may indicate the presence of hydrothermal vents. Once mapping is complete in an area scientists may begin sampling from the floor:

Sediment

Sediment is made up of rock particles, clay, sand and marine snow (clumps of dead/living organisms, dust, faecal pellets). These form layers and by sampling them you can learn about the past. For example, you can determine how close to shore the ocean floor used to be, as large particles sink faster and are nearer to land. Sediment is sampled using corers [2].

Photo credit: [9]

Rocks

The act of dredging along the ocean floor can collect loose rocks. The equipment used consists of chain link bags with a metal-jawed opening towed by ships along the floor. Grabbers/pincers can be used to collect soft rocks that aren’t loose and rock chippers for hard ones [2]. Sampling rocks can provide information on many things including; mineralisation, and Earth’s evolution e.g. how the tectonic plates were arranged [2].

Efforts to map the sea floor have been going on for decades using various techniques. One study used information from two satellites; Cryo-2 and Jason 1, and combined this with data gathered from sonar on ships. Sonar can penetrate the water as it’s sound waves, and when one of these waves hit an object on the ocean floor its presence is confirmed. This sort of survey allows us to observe smaller features and any buried in ocean basins by sediment. The final map showed thousands of underwater mountains, ridges, trenches and even places where the continents pulled apart [7].

Despite advances and discoveries being made, the ocean floor will always be a difficult environment to study. This is due to a number of factors including: [3]

1. Seeing through the water

The seawater will block and absorb any electromagnetic radiation e.g. radio and radar. This means you couldn’t use satellites (radar), alone to map the floor, only gravity and sound (sonar), can penetrate effectively at depth [3].

2. Pressure and temperature

Any equipment used has to endure extreme cold and more than 1,000 atmospheres of pressure to reach the ocean floor [3].

3. Logistics

Due to the remote location if any equipment fails it cannot simply be taken back to land for repair. Any repairs would have to be completed with any tools, spares and expertise on board, therefore a major technological malfunction could jeopardise a research expedition [3].

4. Wave motion

In rough weather, equipment may become damaged and in some cases may be unusable if they cannot be easily deployed or handled [3].


There are many benefits to researching the ocean floor and generating maps. Firstly, estimating the ocean depths and the location of ridges and underwater mountains etc. will help the safe passage of ships and aid in military operations. Secondly, there are commercial benefits. For example, knowing how the continents once fitted together can aid in oil exploration. This is because if you know where an oil field/basin is on one continent you can use it to estimate where a similar one may be located on another if you know how they were once joined. In addition, marine robots can aid commercial fisheries by being able to track tagged fish, allowing monitoring of any changes in distribution or detrimental impacts on stocks [7]. Finally, there is obviously all the knowledge gained from the research that leads to the discovery of new species of marine life, unique environments, and many other things.

Overall, the ocean floor is a remote environment that always has been and will continue to be a source of curiosity. In the future, more detailed maps will need to be generated using sonar on ships. These would allow us to increase the detail in which we can see the floor, therefore further advancing our understanding of this mysterious environment.

References

  1. ‘Just how little do we know about the ocean floor?’, Scientific American: http://www.scientificamerican.com/article/just-how-little-do-we-know-about-the-ocean-floor (Accessed 18.1.17)
  2. ‘Oceanographic Sampling’, National Oceanography Centre: http://noc.ac.uk/research-at-sea/exploration-at-sea/ocean-floor (Accessed 18.1.17)
  3. ‘Chapter 2: History and challenges of ocean studies’, W.W Norton: http://www.wwnorton.com/college/geo/oceansci/ch/02/welcome.asp (Accessed 18.1.17)
  4. ‘TOBI, a vehicle for deep ocean survey’ (1993), C.Flewellen, N. Millard and I. Rouse Electronics & Communication Engineering Journal, 5 Accessed from http://digital-library.theiet.org/content/journals/10.1049/ecej_19930015 on 19.1.17
  5. ‘TOBI launch and recovery August 2012’, Youtube: https://www.youtube.com/watch?v=aGWI1eD9QRE (Accessed 19.1.17)
  6. ‘Autosubs’, National Oceanography Centre: http://noc.ac.uk/facilities/marine-autonomous-robotic-systems/autosubs (Accessed 19.1.17)
  7. ’Scientists create new maps of ocean floor’, VOA Learning English: http://learningenglish.voanews.com/content/scientists-create-new-maps-of-ocean-floor/2478328.html (Accessed 19.1.17)

Picture References

All images are from Wikimedia Commons
  1. Marine Life - https://commons.wikimedia.org/wiki/Category:Underwater#/media/File:Marine_life,_Palau,_February_2012._Photo-_Erin_Magee_-_DFAT_(13252923303).jpg (Accessed 21.1.17)
  2. Sediment Corer - http://commons.wikimedia.org/wiki/File:Gravity-corer_hg.png (Accessed 21.1.17)

Copyright © Reaction Science 2019