Coastal waters are unexpected hotspots for nitrogen fixation

ScienceDaily | 2/21/2019 | Staff
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Knowing where and when nitrogen fixation is occurring will help scientists better quantify coastal waters' ability to absorb and store carbon dioxide and aid in future climate predictions.

"Past models suggested most nitrogen fixation occurred in the open ocean. We found the opposite: Rates are actually higher in coastal areas. They've just been mostly overlooked until now," said Nicolas Cassar, professor of biogeochemistry at Duke's Nicholas School of the Environment, who was senior author on the study.

Activity - Microbes - Diazotrophs - Waters - Study

Most of this overlooked activity is being driven by microbes known as cyanobacterial diazotrophs that live in coastal waters, the study shows.

The tiny organisms take in nitrogen gas (N2) and convert it into ammonia (NH3), a form of nitrogen that phytoplankton, the base of the marine food web, can use as food. This in turn fuels photosynthesis by the phytoplankton and the uptake of CO2.

Distribution - Marine - N2 - Fixation - Role

"This means that we have to revisit the global distribution of marine N2 fixation and re-evaluate its role in the coastal carbon cycle," said Weiyi Tang, a Ph.D. student in Earth and Ocean Sciences at Duke's Nicholas School, who conducted the research as part of his doctoral dissertation.

Cassar and Tang published their peer-reviewed study Feb. 19 in Nature Communications.

Findings - Thousands - Seawater - Samples - Kilometers

Their findings are based on thousands of seawater samples collected from across 6,000 kilometers of the western North Atlantic during two 10-day research cruises in 2015 and 2016.

Collecting that unprecedented volume of data in such a short amount of time at sea was possible, Cassar explained, because his lab team has developed an instrument that allows them to do near-continuous real-time analysis of N2 fixation. They use a method called FARACAS, or flow-through incubation acetylene reduction assays by cavity ring-down laser...
(Excerpt) Read more at: ScienceDaily
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