19. May 2014 How does Nitrogen get into the Ocean?

Nitrogen is essential for most organisms, on land and in water. However nitrogen generally occurs as a gas which is not accessible for many organisms. Only a few microorganisms are able to access gaseous nitrogen and thus they must supply the entire ecosystem. So far the general belief has been that these organisms exist mainly at the surface of the oceans since they simultaneously conduct photosynthesis and need light for this.


Scientists from the Collaborative Research Center 754 “Climate - Biogeochemistry Interactions in the Tropical Ocean“ from Kiel University, GEOMAR Helmholtz Centre for Ocean Research Kiel and the Max Planck Institute for Marine Microbiology in Bremen, funded by the German Research Foundation (DFG), found that there is a much larger spectrum of organisms that can access nitrogen in deep waters. They have published their discovery in the current issue of the renowned journal “ISMEj”.

An important task of modern marine research is improving the predictions of climate change. The nitrogen cycle plays an especially important role in this because nitrogen is a limited nutrient for all life forms in the sea. Particular microorganisms can access nitrogen gas from the atmosphere and store it as biomass. This nitrogen is then supplied to the ecosystem through the food chain and organic compounds. However, so far there has been a great problem with calculating the nitrogen equation. Measurements have indicated that the ocean emitted more nitrogen than it absorbed. In 2010 the marine biologist Wiebke Mohr from GEOMAR pointed out that this imbalance is at least partly due to the methods with which the biological nitrogen fixation process is measured. These methods had underestimated the amount of nitrogen absorbed in the ocean and this seemed to explain the imbalanced nitrogen equation.

The data measured by the new methods is more exact. “Despite the improved measuring of nitrogen fixation, the imbalance in the ocean’s nitrogen equation still could not be completely explained,” says Dr. Carolin Löscher, first author of the published research paper, explaining the impulse for the joint, international study. The team from Kiel University, GEOMAR, the MPI for Marine Microbiology in Bremen, Dalhousie University in Canada, the National University of Ireland, Galway and the University of Southampton in Great Britain succeeded in demonstrating that this discrepancy can be mainly attributed to the fact that not all organisms, involved in these processes are known. "Furthermore, until recently the habitat adopted for the nitrogen fixing was too small. In our study we present a combination of genetic data and measurements from the so-called oxygen minimum zone (OMZ) off the coast of Peru, that has led us to this conclusion," says Dr. Löscher. The OMZs are maritime areas with a very low to non-measureable oxygen concentration levels, although the eastern tropical OMZ in the South Pacific is one of the largest OMZs in the world. The aim of the study was to quantify the nitrogen fixation in this OMZ and to identify key species.

A number of expeditions from the Collaborative Research Center 754 led scientists and scholars to the OMZ in the South Pacific. From the research vessel "Meteor", they took repeated samples, that they later analyzed in the laboratories of the Institute of Microbiology of Kiel University, the MPI Bremen and GEOMAR. The results showed a surprising new diversity of nitrogen-fixing organisms within the OMZ that didn’t have a lot of similar characteristics with the classical nitrogen-fixing organisms. Direct nitrogen-fixing measurements showed rates in the OMZ that usually only occur in large cyanobacterial blooms – which are relatively rare in oceans.

“These results surprised us, since up to now deeper waters were considered unimportant for nitrogen-fixation. The study therefore contributes substantially to closing the gap in the nitrogen budget of the ocean," says Löscher. The results will therefore be used to predict nitrogen-fixation in all the OMZs and oceans because just how productive the ocean will be in the future and how much carbon dioxide can be absorbed from the atmosphere depends critically on this.

Original Publication:
Löscher, C., Großkopf, T., Desai, F., Gill, D., Schunck, H., Croot, P., Schlosser, C., Neulinger, S., Pinnow, N., Lavik, G., Kuypers, M. M. M., LaRoche, J. and Schmitz-Streit, R. (2014) Facets of diazotrophy in the oxygen minimum zone waters off Peru. The ISME Journal, 1-13. DOI 10.1038/ismej.2014.71.

Contact Details

Dr. Carolin Löscher, Tel.: 0431 880-1648

Dr. Boris Pawlowski (Press, Communications and Marketing at Kiel University), Tel.: 0431 880-2104