Researchers discover new source of nitrogen in the Arctic

Without a nitrogen source, phytoplankton in the Arctic has always been limited by the amount of carbon that it can extract from the top layer of the ocean and the atmosphere. The new nitrogen source offered by UCYN-A could make Arctic phytoplankton more productive and, ultimately, reduce carbon levels in the atmosphere.

"It was shocking to find this process in the Arctic," said Deborah Bronk, one of the study's authors and chief executive officer of the Bigelow Laboratory for Ocean Sciences. "We thought that nitrogen fixation only occurred in tropical and subtropical waters, and this discovery could have enormous implications for the ocean's chemical cycles and climate."

Just as garden flowers and other terrestrial plants need nitrogen to grow, this element is also essential for microscopic oceanic plants called phytoplankton. However, most of the nitrogen in the ocean comes in the form of a gas that most organisms, including humans, can not use. Only a few types of microorganisms are able to undertake this task. Scientists have long thought that the main phytoplankton fixing the nitrogen from the ocean lived only in warm waters and that nitrogen fixation was virtually non – existent in the Arctic Ocean.

In 2017, Bronk and his colleagues published an article revealing that nitrogen fixation was actually occurring in the Arctic Ocean, but they still did not know which organism was responsible for the process. They were surprised to discover that the source was UCYN-A, a unicellular cyanobacterium that lives in symbiosis with an algae and usually develops in warm waters.

"One of the things that this study has shown is that our preconceptions keep us from looking for things we do not expect to find," Bronk said. "The more we learn about the ocean, the more we realize that organisms are incredibly plastic in everything they can do and where they can live."

As the Arctic Ocean heats up and the sea ice melts, the phytoplankton growing season lengthens. The research team believes that while UCYN-A has been around for some time in the Arctic, the warming caused by climate change has prompted it to begin repairing nitrogen. They also believe that this change in activity of UCYN-A could, in turn, influence the global climate. As phytoplankton grow, they remove carbon from the ocean and eventually from the atmosphere, but they need nitrogen to do this, which UCYN-A can provide more and more. more.

The researchers estimate that the Arctic UCYN-A currently accounts for about 2% of the world's nitrogen fixation. Continuing to study this process and integrate it into global biogeochemical models will improve climate prediction and understanding of important ocean cycles. The researchers believe that this increase in available Arctic nitrogen could affect biogeochemical cycles in the North Atlantic, resulting in further changes in ocean cycles.

"It's only thanks to previous research that we've been able to identify that this process is new," Bronk said. "This study highlights the fact that it is sometimes extremely important not to find the process you are looking for.We need to preserve the data and make it available to people so that we can actually learn how the ocean evolved."

Explore further:
The fertilization of the ocean by unusual microbes extends to the icy waters of the Arctic Ocean

More information:
Katie Harding et al, Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073 / pnas.1813658115