Life in the Extreme

(August 5th, 2015) What's life like in the deep sea? Ronnie Glud of the Southern Danish University and his team are going to investigate. The biogeochemist recently received a multi-million euro grant from the European Research Council to explore some major trenches in the ocean.

The average oceanic water depth is 3.8 km. Huge areas are covered by abyssal plains, found at depths between 4 and 6 km. However, the hadal trenches can be more than twice as deep witha maximum depth of 11 km. Although there is virtually no difference in temperature between the abyssal plains and the trenches (hadal zones), the pressure increases by approximately 100 bar per kilometre up to 1,100 bar, i.e. 1,100 times more than above the water surface.

Is this environment suitable for life? Not human life that's for sure. Ronnie Glud and his team at the University of Southern Denmark in Odense use robots to examine sediments of ocean trenches. The extreme conditions require very sophisticated equipment. “We develop most of these unique instruments by ourselves,” explains Glud. The equipment ranges from tiny micro-sensors to  large-scale robots and underwater vehicles. Most researchers have no specific technical background and much designing was ‘learning by doing’. In addition, the scientists collaborate closely with specialised companies and engineering teams for many sophisticated tasks in the development of robots.

Amongst others, Glud collaborates with a group at the Max-Planck-Institute in Bremen, Germany, where he used to work. This group, now headed by Frank Wenzhoefer, develops technology for projects in extreme environments, not only for deep sea exploration but also for astrophysical projects. Another important collaboration partner is the Agency for Marine-Earth Science and Technology in Japan with extensive experience in deep sea explorations and access to sophisticated logistics platforms – such as specialised ships.

So far, Glud and his colleagues have found several life forms in the deep ocean trenches: bacteria, archaea, viruses and meiofauna, small-sized organisms, like nematodes of less than 1 mm. Even a large antipode has been observed at 10.8 km depth for the first time. “The extreme pressure in the trenches affects thermodynamics and the way that life can operate. Cellular processes, membranes and enzymes, for example, have to be very well adapted to these conditions,” explains Glud.

Three different approaches will be used to examine specialised bacterial and archaeal communities in the sea bed. For laboratory investigations, the sediments of the trenches together with the organisms are chemically fixed and then brought to the surface. Thereby, the cells stay intact and DNA as well as RNA can be sequenced and investigated to examine the abundance and activity of the specialised extremophile microorganisms. Another approach is to inject labelled organic substances in situ into the sea bed and follow their chemical transformation rate. Finally, microsensors are used to measure the metabolic activity of the bacteria and archaea in the sea bed. How much oxygen is consumed in the sediments of the trenches? How much organic material is degraded? And how much organic material is deposited at these depths at all? Together these complementary approaches help Glud to get an idea of how life functions in this extreme environment.

“We are interested in relationships between life and chemical conditions on the planet,” says Glud. Such work includes micro-scale investigations to understand the life of the responsible microbes but also to compare conditions and activities in different deep sea environments for upscaling the results. How important are deep sea trenches for the overall carbon and nitrogen cycle on earth? How does the metabolism of microbes regulate the chemistry of the ocean? Up to now nothing is known about the impact of hadal zones and their inhabitants. “Our hypothesis is that trenches receive relatively high loads of material and that specialised life forms can feast on this material. Furthermore, we hypothesise that trenches as such work as hot-spots for the deep sea carbon cycle,” explains the biogeochemist.

In the past, Glud and his colleagues focussed on the chemical and metabolic processes of the organisms. During the upcoming expeditions, they will also look for the species themselves. Glud: “I guess we will discover unique life forms that have not yet been described. They will probably differ from everything else in the rest of the ocean.”

The overall goal of Glud’s research is to estimate the amount of organic material deposited in the deep sea and to find out how much of it is degraded by different processes in the sea bed. Within the next five years, three different trenches will be investigated: the Atacama Trench, the Japan Trench and the Kermadec Trench. All are located in the Pacific at a depth between 8 km and 10.5 km, but due to differences in productivity, the amount  of 'food'( in the form of organic material) received varies greatly. Therefore, it will be very interesting to compare life and biogeochemistry at these extreme but different environments.

Glud will be on board during all of the 6 - 8 scheduled expeditions accompanied by some colleagues to operate the robots and collect samples as well as data that will probably shed new light on life down in the dark depths of the ocean.

Stefanie Haas

Photo: R. Glud/USD

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