A new study led by the UK's National Oceanography Centre (NOC) has discovered that tiny organisms living on particles in the water, such as sinking organic material, may be an important source of nitrogen in the Arctic Ocean.
The findings, published in Nature Communications, reveal a previously overlooked source of this vital nutrient, which could help scientists better understand how Arctic marine ecosystems respond to a warming climate.
Nitrogen is essential for marine life. Its availability can help determine how much life an ecosystem can support, from microscopic organisms at the base of the food web to the animals that depend on them.
Researchers studying the Barents Sea found significant levels of nitrogen fixation taking place below the ocean surface. Nitrogen fixation is a process in which specialised microorganisms convert nitrogen gas into forms that other organisms can use to grow.
The study found that microorganisms living on tiny particles play a key role in nitrogen fixation in the Barents Sea. This differs from patterns observed in warmer ocean regions, highlighting how the organisms responsible for supplying usable nitrogen vary between marine environments.
These findings provide an important new insight into how nitrogen is supplied in the Arctic Ocean and could help scientists understand how this may change as the region warms. As the Arctic changes, some of these processes could begin to resemble those already observed in warmer, subtropical oceans.
Dr Mar Benevides, lead author of the study, said: “Our findings reveal a previously overlooked source of nitrogen in the Arctic Ocean that is not currently accounted for in global estimates of nitrogen fixation. Nitrogen is a vital nutrient that supports marine food webs, so understanding where it comes from is essential to predicting how ocean ecosystems will respond as the Arctic warms.
As the Arctic becomes more nutrient poor in some areas, these sources of nitrogen could become increasingly important. Our research highlights how much we still need to understand about the processes sustaining life in a rapidly changing Arctic Ocean.
However, the researchers caution that the process observed in the Barents Sea may not occur in the same way across the entire Arctic Ocean.
Dr Benevides added:
The Barents Sea is strongly influenced by the inflow of Atlantic water, as well as changes in sea-ice extent and inputs from land. These factors influence nitrogen dynamics in different ways across the Arctic, meaning further research is needed to establish how widespread particle-associated nitrogen fixation is and what controls it.
The N-ARC project was funded by Natural Environment Research Council (NERC) Discovery grants for Nitrogen fixation in the Arctic Ocean (N-ARC; grant numbers NE/T001240/1 and NE/T000570/1), held at the University of Liverpool (CM), University of Southampton (MCL) and the National Oceanography Centre Liverpool (JEH). Funding was also provided by the BIOPOLE project, funded by NERC, under the National Capability Science Multi-Centre award scheme (NC-SM2).
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