How to... research the ocean floor with automation

Materials World magazine
,
1 Aug 2018

The world’s deep-sea trenches are mysterious and relatively unexplored areas with the potential to influence the world’s climate. Automation is helping to analyse and answer the questions of the oceans depths, as Faulhaber explains.

What influence does hell have on heaven? This is not an issue of theology – marine scientists refer to the deepest depths of the oceans as the hadal zone, named after the shadow empire of the ancient Greeks. They do, however, suspect that more life exists down there than in the mythical Hades. 

While Mars is millions of kilometres away from Earth, its surface is better studied than the floors of the deep-sea trenches, which lie only eight-to-11km below the sea surface. The biological and chemical processes that transpire there are, in fact, still largely unknown. A research project, appropriately named Hades-ERC, is aiming to change this and supply completely new insights into the depths of the oceans. 

It was initiated by Professor Ronnie Glud of the University of South Denmark, Odense. ‘In marine biology, there is actually a simple basic rule’, he says. ‘The deeper you go, the less life one finds.’ With increasing depth, it becomes colder and darker. Less of the food produced in near surface water reaches the great depths. Moreover, the water pressure increases by one bar every 10m. At a depth of 10,000m, the pressure of approximately 1,000 bar – 1,000 times higher than on the ocean shore. ‘But, gravity exerts its effects even in this environment. A portion of the organic material that sinks to the deep ocean floor ultimately lands in the trenches, where it collects,’ says Glud.

Collection basin for organic material

Thus, it was no surprise to Glud when he found highly active microbial communities at a depth of nearly 11km in 2013. At that time, he had descended the instruments into the Mariana Trench in the Western Pacific. ‘We found more organic matter at depths below 10,000m than at 6,000m’, he explains. ‘We therefore assume that the trenches have a disproportionately high influence on the nitrogen and carbon balance of the seas. Although they account for only 2% of the ocean area, they could have a disproportionately high effect on the carbon footprint and climatic occurrences.’ 

The Hades-ERC project aims to better understand the processes in the trenches. It is financed by the European Research Council. An advanced grant totalling €2.5m allows the scientists to conduct long-term, open-ended basic research. In addition to Glud’s department, marine biologists at the University of Copenhagen, Denmark, as well as marine research institutes from Germany, Japan, and Scotland are involved. 

The sophisticated instrumentation is developed as a joint venture between the team in Odense and a German team headed by Dr Frank Wenzhoefer, based at the Max Planck Institute in Bremen. The project is scheduled to last five years. The studies begin Autumn 2018 in three Pacific trenches – the Japan, the Atacama, and the Kermadec Trench – at depths between 8,100 and 10,900m. These formations were selected because the organic load in the waters above them is different to each other. They offer their microbial inhabitants widely varying conditions.

Robots instead of submarines

While manned dives have already taken place to such depths, the use of submarines would not be practical for extensive research of bottom sediment. The project team therefore developed robots that independently descend to the sea floor and carry out pre-programmed studies. 

They are equipped with sensors that, among other things, can measure the oxygen intake of the bacteria – a value from which one can make deductions on the quantity of the processed organic material. Other sensors help answer the question of whether deep-sea microbes breathe oxygen, nitrate, or sulphate. 

‘To survive under the extreme conditions of the deep sea, the bacteria must be very different to their relatives in shallower waters’, Glud says. ‘For example, their membranes and enzymes must function in a completely different way. How exactly, is what we want to learn.’ It is a special challenge to study the microbes themselves. Because they have adapted to an environment with enormous water pressure, they cannot simply be brought to the surface. They would turn into a soup on the way up. The Hades-ERC robots are, therefore, provided with equipment that can inject a fixing agent into the sediment, which keeps the microorganisms intact during recovery.

Prerequisite – pressure resistance

While the microbes need to be protected from the decreasing pressure as they are brought to the surface, special precautions must be taken for the equipment in the robots to protect it from the extreme pressure in the trenches. The sensors, as well as the tools for handling the sediment, are specially designed for this environment and can withstand the pressure. To perform their work, they do, however, need to come into contact with the sediment and must be moved into various positions.

Responsible for this movement are DC-micromotors of series 2342 CR from Faulhaber, provided with encoder and the appropriate planetary gearheads. While some components are housed in a pressure stable titanium cylinder, some devices like the motors and gearboxes can only perform their work when in contact with the surroundings that are to be studied. ‘We therefore inserted these components into another cylinder in a small flexible membrane which is filled with an inert fluid,’ Glud explains. ‘The membrane ensures that the water pressure affects the enclosed components without a pressure difference occurring – because this would crush the motors.’ 

In an earlier version of the robot, various motors were used for the different tasks. In practical tests, the team came to the conclusion that it makes more sense to work with just a single, especially robust motor type. ‘The robot remains at its operation site for many hours before returning to the surface with the samples. During this time, it operates completely autonomously,’ Glud explains. ‘Our success is dependent on – among other things – the flawless function of the devices during this time. Thus, the motor needs to be extremely reliable, compact and strong.