The journal Nature Communications has just published a study by the University of Vigo, the Spanish Institute of Oceanography (IEO) and the Spanish National Council for Scientific Research (CSIC) that carries out an experimental assessment of nitrogen contributions to plankton in the global ocean. Nitrogen is an essential element for life, without which plankton algae would not be able to capture atmospheric CO2 through photosynthesis and feed the food web of marine ecosystems. “The biological productivity of a large part of our seas and oceans is naturally limited by the availability of nitrogen in the water,” explains Bea Mouriño-Carballido, professor at the Department of Ecology and Animal Biology at the University of Vigo. In the surface ocean, far from the coasts, the most important processes for the supply of nitrogen are diffusion from deep waters, rich in nitrate, and the incorporation and use of nitrogen gas from the air (N2), “something that only a few specialized microorganisms are capable of”, points out the researcher from the Biological Oceanography Group (GOB), Mouriño-Carballido.
The results of the research carried out during the Malaspina Expedition contradict previous studies and show that, although the use of atmospheric nitrogen is important, more than 80% of the nitrogen reaches the light zone by turbulent diffusion from deep waters. “Our data indicate that double diffusion processes mediated by what we call ‘salt fingers’ function as fast transport routes and contribute 20% of the nitrogen in tropical and subtropical regions of the Atlantic and Indian Oceans”, says Bieito Fernández, who is about to complete his doctoral thesis at the University of Vigo. The research was funded by research projects granted by the Ministry of Economy and Competitiveness and in addition to Bea Mouriño-Carballido and Bieito Fernández, the main author of the study, two other members of the research group, professor Emilio Marañón and technician Paloma Chouciño, who are co-authors of the work, participate in it.
The study, published Wednesday in the journal Nature Communications, was conducted during BIO Hespérides’ seven-month voyage around the world. Experiments were conducted to measure the use of atmospheric nitrogen, while observing the cyanobacteria responsible for this process under a microscope. Simultaneously, nitrate concentrations were measured from the surface to the dark waters, and instruments were launched to assess the level of turbulence and the vertical pumping capacity of nitrogen.
According to Rafael Simó, a researcher at the CSIC and one of the coordinators of the expedition, “we owe half of the planet’s oxygen production to the oceans and the removal of a significant part of the CO2 that humans release into the atmosphere, in addition to fishing resources; nitrogen acts as a key to regulating all of this, so understanding the nitrogen cycle is crucial to understanding and anticipating the role of the oceans in the climate and the food supply of future generations.” The nitrogen necessary for photosynthesis to occur in the illuminated surface part of the ocean comes from the use of N2 from the air by some microorganisms and the diffusion of nitrate from deep waters. The study published today evaluates both processes in the planet’s oceans.
