Why didn't we explore the ocean rifts

Scientists set sail to explore the depths of the Atacama Trench in the eastern Pacific

The expedition aims to research life in a water depth of 8,000 meters in order to understand the importance of the trench for regional carbon and nitrogen recycling.

On March 2nd, an international scientific team - led by Professor Ronnie N. Glud, University of Southern Denmark in Odense, and Dr. Frank Wenzhöfer, Max Planck Institute for Marine Microbiology in Bremen - on the German research ship SONNE on a 32-day trip to the Atacama Trench in the Pacific Ocean.

The Atacama Trench, which is located off the coasts of Peru and Chile, is one of the deepest ocean trenches in the world with a maximum depth of 8065 meters. It is almost 6000 kilometers long.

The research trip is part of Glud's European Research Council Advanced Research Grant project HADES-ERC, which aims to understand the biogeochemical processes and microbiology in the deep sea regions of the oceans. The researchers therefore have a number of autonomous instruments on board the ship to investigate different locations along the Atacama Trench.

Microbial communities play an important role in the functioning of the world's oceans and in life in the oceans and on land.

“The deep-sea trenches are among the least explored habitats on earth and probably contain many unknown forms of life. Recent studies suggest that the trenches represent areas of increased biological activity in the deep sea, even though the sea floor is exposed to extreme hydrostatic pressure at these depths, ”says project manager Glud from the University of Southern Denmark.

“We use innovative in situ technologies to explore this extreme habitat, which research often fails due to the major technological challenges that come with working under such high pressures. Different autonomous systems - so-called landers - help us to examine the microbial processes directly on the sea floor, ”says chief scientist Frank Wenzhöfer from the Max Planck Institute for Marine Microbiology.

The Atacama Trench is located beneath one of the most productive ocean regions in the world, and so researchers expect it to contain large deposits of organic material that sinks from the slopes of the trench and the layers of water above and collects at the bottom.

“We expect there will be significant anaerobic degradation of organic matter in the trench sediment. This makes the ditch a unique place where we can research processes of the nitrogen cycle and sulfate reduction under extreme pressure conditions - probably previously completely unknown microbial communities are responsible for this, ”says Glud.

Specific questions of this research trip are:

  • Which sedimentary processes provide the nourishment for the hadal community in the Atacama Trench?

  • How do the biodiversity, diversity and community structure of microorganisms, meio- and macrofauna in the Atacama Trench differ from trenches in less productive regions and nearby deep-sea and shelf areas?

  • What are the general biogeochemical characteristics of the surface and deep sediments and the water column in the eutrophic atacama trench?

  • How exactly does the mineralization proceed during the decomposition of organic material in the eutrophic atacama trench?

  • How efficiently do the microbial communities work under extreme hydrostatic pressure conditions in the mineralization of organic material compared to communities in shallower areas? And to what extent do specialized, previously unknown, extremophilic microbial communities influence these processes?

Past and future expeditions in deep sea trenches

In 2010, Glud and Wenzhöfer took part in a Japanese-led expedition into the Mariana Trench and recovered sediments from the deepest part of the world, the Challenger Depth at a depth of almost 11,000 meters. They found a surprisingly high level of microbial activity in this hostile, extremely high pressure environment (the pressure is almost 1,100 times higher than at sea level). Since then they have participated in various other research trips into hadale rift systems.

In 2017 Glud carried out an expedition into the Kermadec Trench and recovered sediments from a depth of 9994 meters. He used it to research the conditions in a trench that is characterized by a relatively low input of organic material. In addition to the upcoming expedition in the Atacama Trench, there will be another one in the Japan Trenches.

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