An ultra-sensitive oxygen sensor developed by a researcher from Aarhus University in Demark may provide a new understanding of the importance of seas in the global nitrogen cycle

You cannot see it from the deck of the vessel, but the ocean off the west coast of South America is short on oxygen. Researchers tend to designate the area an “oxygen minimum zone”. However, as articles in the scientific journals PNAS and Science recently made clear, we need to rename the ecosystem – as there is quite simply no oxygen here. It was the invention of an extremely sensitive oxygen sensor that enabled researchers to make this surprising observation. The sensor was developed by Niels Peter Revsbech, Professor of Microbiology at Aarhus University.

The tiny measuring device is now setting the agenda for the future work of a range of leading researchers. Measurements taken using the oxygen sensor are to show what the concentration of oxygen means for the lives of micro-organisms in areas around oxygen minimum zones – and how the fact that these zones are expanding in step with the progress of global warming is affecting the global nitrogen cycle.

Zones remove nitrogen from the sea

Researchers currently know very little about conditions in the low-oxygen zones, which account for only approximately two per cent of the total area of the seas today. Nevertheless, it is in these zones that around half of all nitrogen removal from the oceans takes place.

“These oxygen minimum zones are natural phenomena, and seem to act as nature’s own purification plants. The marine currents supply nitrogen fertilizer, which has either been created through natural processes or produced industrially, and this is removed by the bacteria in the seawater,” explains Niels Peter Revsbech.

“Nitrogen is an important fertilizer for plant plankton, and an understanding of the limiting conditions for the production of plankton in the sea is the key to comprehending the role the seas play in the global environment.”

Reveals hardy bacteria

The results researchers have gleaned from the oxygen minimum zone off the west coast of South America are providing completely new knowledge about the lives of the organisms and the biological turnover in this special ecosystem.

“Our very precise measurements reveal that bacteria can utilise much lower concentrations of oxygen than we previously though possible. A common coli bacterium can divide and grow in an environment with less than one hundred-thousandth of the oxygen that is to be found in normally aerated water,” says Niels Peter Revsbech.

The new sensor has also made it possible for the researchers to measure oxygen turnover directly in the seawater and, for example, observe how the bacteria in the water react to the substances that micro-algae produce.

It has not previously been possible to observe the biological turnover in ocean water as directly as can now be done using the new sensor.

Key role for sensitive sensor in new projects

There will be no shortage of work for the sensor in the future, as it has been given a key role in numerous new research projects:

“The new technology has a crucial role to play in answering fundamental questions about how oxygen regulates the life and growth of marine organisms,” explains Donald Canfield, Professor of Biology at the University of Southern Denmark.

Together with Professor Niels Peter Revsbech and a number of other researchers, Professor Canfield has just been awarded a project grant of DKK 19 million from the European Research Council. The goal of the project, which the researchers simply call “Oxygen”, is to build up a complete picture of the significance of oxygen concentrations to the world’s microbial ecosystems.