Thirty to fifty percent of the global conversion of nutrients to nitrogen gas occurs in these areas. In ‘The Proceedings of the National Academy of Science of the United States (PNAS)’ of Tuesday 19 April, researchers from Bremen and Nijmegen state that this conversion is not carried out by denitrifying bacteria, as was believed for decades, but by anammox bacteria. Nitrogen compounds act as fertilizers and are the ecological basis for any lifeform on earth as these compounds limit the overall growth rate.
The researchers discovered this type of bacteria for the first time a few years ago in the oxygen poor Black Sea and now also in the open ocean. This discovery has major consequences for our understanding of the global nitrogen cycle. The Benguela current system leads to upwelling of nutrient-rich cold water off the coast of Namibia and acts as a kind of snackbar in the tropical ocean, which is visited by many animals including giant whales. The newly discovered anammox bacteria remove ammonium from the ocean, which as a result can not be taken up anymore by other organisms. Algae and cyanobacteria only partly succeed in fixing the released nitrogen gas to form new nutrients that can be fed into the nutrient cycle again.
In the article in PNAS, researchers from the Max Planck Institute for Marine Microbiology (Bremen, Germany) and the Institute of Water and Wetland Research (IWWR) of the Radboud University of Nijmegen show for the first time that anammox bacteria are present in the Atlantic ocean in oxygen poor waters at ~100 m depth. The number and activity of anammox bacteria present at this depth is sufficient to remove the ammonium that rises up from deeper waters and the seafloor. A unique combination of microbiological methods involving high resolution nutrient profiles, experiments with stable isotope labeled nutrients, depth profiles of unique membrane lipids (ladder molecules), fluorescence microscopy and DNA analyses of water samples was used to proof the abundance of anammox bacteria in the Atlantic Ocean. The discovery of anammox bacteria in the open ocean has major consequences for our understanding of the global nitrogen cycle. Models of global nitrogen budgets, which play an important role in long term climate predictions, will have to be revised. The discovered nitrogen loss has also consequences for the carbon cycle in marine ecosystems.
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