In deep water

If it was not already obvious, last year’s Boxing Day tsunami hammered home the point with devastating force: we know next to nothing about what is happening beneath the world’s oceans. However, an ambitious European project to install and network up to 120 deep-sea observatories early next decade will, for the first time, supply scientists with continuous real-time monitoring of what is really going on down there in the mysterious depths of the sea.

The European Seafloor Observatory Network (ESONET) is large both in scale and ambition. Around 10 regional networks of cabled underwater observatories will be installed at an estimated cost of around €200m (£140m). From the Arctic north to the milder waters of the southern Mediterranean, ESONET will provide real-time images and data from an area of approximately 3,000,000km² at depths of up to nearly 5km beneath the surface. Incorporating a vast array of scientific instruments, sea-floor sensors, autonomous underwater vehicles (AUVs) and more than 5,000km of fibre optic sub-sea cables, it will also provide the sub-sea component of the EU’s Global Monitoring for Environment and Security (GMES) programme, monitoring the seabed for seismic activity that could lead to tsunamis.

Alongside the observatories and cable networks, ESONET will incorporate a number of other underwater projects. Some of these, such as the Greek project NESTOR, are already operational whereas others including giant underwater neutrino detectors like the planned KM3Net are still being planned.

Aberdeen University’s Prof Monty Priede, who is leading the ESONET project, explained that the initiative will address the long-standing frustrations of oceanographers. Most existing underwater research has relied on surface ships indirectly observing the area below them with instruments suspended or deposited from the ship. Instruments sent to the ocean floor are fuelled by battery packs and are limited in the amount of data they can hold. Only when the instrument is retrieved can it provide its readings. Satellite imagery is not much help either, as it can penetrate only up to a few metres beneath the ocean’s surface, revealing nothing about the complex deep-sea currents that have such an impact on our climate.

ESONET’s scale will require not only a huge amount of planning and technology as well as finding a substantial amount of funding.

Meanwhile, EU scientists will be watching with interest events taking place just off the coast of Canada, where in 2007 a $300m (£170m) joint US/Canada project called Neptune will turn a 200,000km² area of the Pacific Ocean into a research laboratory.

More than 3,000km of fibre-optic power cables will criss-cross the Juan de Fuca tectonic plate, anchored by more than 30 nodes, which will act like underwater power supplies to which research instrumentation can be connected. The cable will be buried 2,000-3,000m below the surface, where it is safe from passing ships and where oceanographers can study activity on the seabed. Much of the technology that will be used in ESONET will be tested here.

Managed by the University of Victoria in Canada, the first part of the Neptune project will lay an 800km ring of powered fibre-optic cable on the seabed over the northern part of the tectonic plate, a 200,000km²region in the north-east Pacific, just off the coasts of British Columbia, Washington and Oregon. The Neptune cable network will initially feature two seafloor laboratories, one on the northern edge of Barkley Canyon, the other close to deep-sea hydrothermal vents along the so-called Endeavour Ridge.

These unusual chimney-like structures are formed when seawater seeps deep into the Earth’s crust through cracks in the ocean floor. This water is then heated by magma and rises back to the surface gathering chemicals from the rock on the way and emerging as a black 360 degrees C chemical soup. Scientists have recently discovered that the extreme environments around these vents can support life, and may provide us with clues to the possibilities of life surviving on even the most inhospitable of planets.

Currently, finding out more about them has largely been a hit-and-miss affair, with submersibles and probes launched from ships that are dependent on favourable weather and the luck of the draw to time their annual visits with the most dynamic seabed activity.

In Neptune instruments including video cameras, nutrient monitors, wave sensors and remote-control robotic vehicles will be permanently stationed in the icy waters, providing scientists with unprecedented real-time information about activity beneath the waves. The instruments will also be interactive so that scientists can instruct them to respond to events, such as storms, plankton blooms, fish migrations, earthquakes, tsunamis and underwater volcanic eruptions, as they happen.

As a test-bed for much of the technology to be installed, two smaller projects are taking place nearby: Mars and Venus. The contract to install the fibre-optic cables for the larger of these, Venus, was won by Chelmsford marine cable company Global Marine Systems, working in tandem with a Canadian company, Oceanworks. According to Phil Hart, Global’s director, laying cables for scientific research is very similar to the work they do on sub-oceanic telecommunications cables except these cables end at an interface unit beneath the sea, the node, rather than linking two landmasses.

Laying fibre-optic cables involves a large amount of pre-planning because the route must be mapped out in great detail. To survey the topography of the seabed, engineers use multiple sonars built into their survey vessels. Global Marine Systems has developed a proprietary computer modelling system, Cable Lay Planner, that helps calculate how best to lay the cable.

For example, if two hills on the seabed lie roughly 100m apart there is the possibility that the cable could end up being suspended between the two. This can result in ‘vortex shedding’ which means that because the cable does not lie snugly along the seabed it will pick up vibrations and will quickly become damaged through fatigue. The software takes such topography into consideration and advises on a number of factors that affect the way in which the cable will be installed.

Ocean currents add an additional layer of complication as they can cause the cable to drift in the sea. ‘We have to know about the topography to control the speed of the ship, the tension of the cable and the speed at which it is being paid out. By controlling these factors you can make the cable follow the shape of the seabed,’ said Hart.

The installation of scientific cabling also calls for a far greater degree of accuracy than telecommunications cables. In the latter, it is only expected that the cable is laid within a corridor of around 100m. However, for underwater installation, as each node location is chosen specifically because it is a site of scientific interest, the placement of the node has to be accurate — for the Venus project no more than 2m either side of the locations the scientists have specified.

Laying the cable itself is also more complicated than simply feeding it out from the back of a ship. If a cable is to be placed in water shallower than 1,500m it must be buried in the seabed to protect it from damage by shipping trawlers. In shallower water like this the cable is fed through a deep-sea plough, a machine that ploughs a furrow up to 3m into the seabed and feeds the cable into the trough it has created. However, the seabed can be unforgiving — from time to time the plough must be winched back on-board the cable ship for minor repairs and to check that everything is functioning correctly. These withdrawals from the seabed result in some sections of the cable not being completely buried, so remotely operated underwater vehicles (ROVs) are pressed into action.

Global Marine Systems has around 200 different-sized ROVs, equipped with manipulators to carry out a variety of tasks and bristling with hundreds of underwater cameras. The robots eject water through twin jet legs that are stored horizontally during deployment but move to an incline of about 70^o when preparing to dig a trench.

The ROV straddles the cable as it is fed out from the ship with the water that is pumped out of the jet legs leaving a trench full of ‘fluidised’ soil in the craft’s wake. A depressor arm then pushes the cable down into the trench as the ROV passes along, with the soil quickly settling back and compacting on top of it over time. ROVs with different power specifications are used depending on how deep the cable is to be laid, with a 200HP model able to bury to about 1m deep, and a 400hp ROV digging 2m down.

Another challenge for engineers is that the science experiments at the nodes need a huge amount of power compared to the relatively low power consumption of telecommunications cables. This leads to problems with the electrodes that transfer the power at the nodes, which had to be redesigned to compensate for material loss.

The difficulties imposed by the observatory’s huge power demands also led Alcatel — which won the contract for Neptune and hopes to be involved in ESONET — to develop a unique power system for this new breed of underwater observatory. As part of the Mars project at Monterey Bay, Alcatel’s London-based team worked with engineers at NASA’s Jet Propulsion Laboratory to develop a DC-DC power supply that was able to convert massive voltages into smaller voltages that could be used with science instruments, all to take place more than 1km underwater.

The converter will change a 10kV supply into 400V, which can then be used with the science modules. Encased inside a 1m-long pressure tube, 48 individual high-frequency resistors switch the DC to AC, a transformer lowers the voltage and then another circuit changes it back to DC. The high-voltage input is co-ordinated by a single automatic controller which prevents any one converter being exposed to the entire 10kV input, which would destroy it.

Alcatel’s submarine marketing director Gary Waterworth has been heavily involved in technical discussions for ESONET. In his opinion the most important aspect of this power supply, under development at Alcatel’s Greenwich base, is that it can survive for long periods of time deep underwater. ‘These systems are so far offshore you cannot afford to keep maintaining them. The scientists want them where there is a lot of activity such as where there is likely to be an earthquake. These are areas we would normally avoid so these nodes have to be particularly robust and allow for shocks and strains,’ said Waterworth.

Unsurprisingly, robustness is a recurring theme when you are discussing underwater observatories. The science nodes themselves, like gigantic car-sized power sockets, are encased in waterproof titanium, while the cabling systems are designed to be able to continue working should one of the spurs accidentally malfunction. These nodes will allow up totwo gigabits of data to be transferred from the instruments and passed along the cables to be studied by land-based scientists in real-time via the internet.

Keeping scientific instruments for long periods underwater is nothing new but, whereas in the past researchers could haul out the equipment periodically to check its results and to provide maintenance, it would be impractical to manually maintain either Neptune or ESONET’s legions of instruments.

One innovative new system that will take advantage of the extra bandwidth and data throughput available to Neptune’s scientists is an array of hydrophones that are sensitive enough to track a range of noises, from the distant rumble of shipping to the sound of wind, rain and lightning. However, while the cabling and nodes are designed to last for at least 25 years the science instruments are likely to be much more temperamental; the hydrophone is guaranteed for only one year, for example. According to Neptune’s director of engineering, Peter Phibbs, keeping the instruments in working order is a challenge that has not yet been satisfactorily resolved.

‘One of the most obvious difficulties is contamination by things like algae growing on the sensors. This is particularly a problem if you are using chemical or DNA sensors,’ he said. ‘The other is calibration. In most of these instruments, particularly the most sensitive ones, the calibration will wander over time so you need a way of determining how much it has changed and be able to recalibrate it in situ.’

One possible solution, which the French marine institution IFRIMIR is investigating, is to use the power that is coming into the instrument to power either wipers to clean the camera lenses or even to heat the casing.

Whatever the solution to the myriad problems that deep-sea observatories raise, Monty Priede and the consortium of institutions involved in ESONET will be monitoring Neptune closely before work begins on their own hi-tech window into the deep oceanic unknown.