October 19, 2021

I, Science

The science magazine of Imperial College

This article is taken from the Winter 2011 issue of I, Science.

Juan Casasbuenas explores the mysterious world of the deep sea and the extraordinary technology being used to find out exactly what’s lurking beneath the surface.

The mission has been going for hours. The atmosphere is tense. In the dark room, multiple screens feed the pilot information about the mysterious world being explored remotely. The instruments indicate an extreme pressure and a temperature of about 3°C. Salinity levels are through the roof and oxygen levels minimal. The camera feeds display nothing noteworthy.

The pilot extends the remote manipulator arm of the vehicle by operating the controls; the arm is equipped with an array of sensors and has a strong light that reveals tiny particles gliding across the screen, reminiscent of a light snow flurry. As the pilot ponders the hostility of this eternally dark world, a hint of movement captures his eye on one of the other screens. He carefully adjusts the camera to capture it and focuses the image, revealing a surreal figure …

This scene may evoke ideas of space exploration or even science fiction, but it is in fact a mission into the deep sea. The deep sea is a hostile world:beginning at a depth of 1800m and culminating at about 11000m, it isdeep enough to comfortably submerge Mount Everest.

“Two thirds of the surface of our planet is deep-ocean floor – it is the dominant habitat, we are the aliens,” explains Deep sea biologist Dr BrianBett,from the National Oceanography Centre in Southampton.“The exploration aspect can certainly be exciting and intriguing – many of the places I visit, the landscapes I map, and the animals I encounter are previously unknown.”

Humans have reached the bottom of the ocean using submersibles but never set foot on it – the extreme pressure would crush us instantly. DrBett adds: “a dozen men have walked on the moon; no one has or is likely to walk on the deep-ocean floor. A visit is possible by submersible, but with only three suitable vehicles in the world, your chances are pretty slim.”

Much of what we learn about the deep sea therefore relies on the use of highly sophisticated unmanned vehicles. Remote Operating Vehicles (ROVs) like Ventana from the Monterey Bay Aquarium Research Institute (MBARI) are piloted from a mission control room on board a ship at the sea’s surface.

The vehicles are equipped with numerous gadgets, including high definition cameras, hydraulic thrusters, fibre optic telemetry, variable buoyancy systems and even mass spectrometers, all helping to unravel the puzzles of the deep. Another, newer generation of vehicles are autonomous underwater vehicles known as AUVs, such as NASA’s Jaguar. Jaguar is currently being used to map the ocean floor, and evolutions of it may one day visit the deep ice covered oceans of Jupiter’s Europa.

In DrBett’s view, AUVs have the capability to “revolutionise the detailed mapping of the deep-sea floor. They are unmanned and untethered systems that carry out pre-programmed diving missions, but have sufficient intelligence to avoid and navigate around obstructions.”

Life and Biodiversity
The strange figure is a fish; now in focus it flaps its large fins but remains unperturbed by the encounter. The light from the ROV reveals something curious about it…a transparent head. Before the pilot can have a closer look, the fish disappears into the darkness, never to be seen again.

Footage of this oddity –the barreleye fish Macropinnamicrostoma– was first recorded during one of these fleeting encounters by researchers at MBARI. Its strange adaptations include tubular eyes and a transparent head. Its eyes are found at the topof its head, enclosed in transparent shields like the canopy of a jetfighter. Its eyes can rotate within the shield in order to peer up towardsfalling pieces of organic litter – marine snow- or faint silhouettes of prey. Other oddities include angler fish (Melanocetusjohnsonii) that use a bioluminescent growth on their head in order to lure and capture prey, sea worms that release glowing bombs to thwart attacking predators and predatory sea squirts that lay ‘leaves’ on the ocean floor which trap unsuspecting shrimp or worms that walk across them.

Although every descent into the deep sea brings with it intriguing new findings, describing all these new species remains a huge challenge due to the shortage of taxonomists across all fields of biology.

DrBett explains it best: “The diversity of the deep sea is comparable to any ecosystem on earth, but despite being the foundation stone of all biology, and critical to ecology and biodiversity – taxonomy remains extremely difficult to fund. So for now, and for a long, long time into the future, the deep sea will contain more unknown than known species.”

The pilot operates the controls and the long treacherous ascent to the surfacebegins; another journey into the abyss comes to an end.

More > Read the full interview with Dr Brian Bett.

Image: © 2004 MBARI