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Eddies: walls in the sea
An international team of researchers, participated by IFISC scientists (Institute of Cross-Disciplinary Physics and Complex Systems, joint center UIB-CSIC), has established the relationship between eddies and hypoxia areas in the oceans. Between the 7% and 8% of the oceans’ volume are zones with a very low content of oxygen and, therefore, there is practically no life. Now it has been discovered the mechanism that prevents oxygen to enter into these areas (by ocean currents, for example), despite that in the sea there are no barriers, apparently.
Nature Geoscience publishes this research developed at IFISC by Joao Bettencourt (now postdoctoral fellow at UCD, Ireland), Cristóbal López and Emilio Hernández-García; in collaboration with researchers from the Geophysical Institute of Peru, the Laboratoire de Études in Géophysique you Oceonographie Spatiales in Toulouse (France), and GEOMAR centre in Kiel (Germany) on the Peruvian oxygen minimum zone, studying the role developed by mesoscale structures, essentially eddies and marine fronts.
Through the application of mathematical numerical models (realistic models of ocean circulation and Biogeochemistry in the Peruvian area) and analyzing data with techniques of the Physics of chaos, the team has come to the conclusion that eddies, acting as walls, are the responsible to keep oxygen out of these regions. This study also reveals that, paradoxically, the same swirls sometimes, sporadically and quickly, introduce water with high amounts of oxygen in these areas.
The origin of the minimum oxygen area studied, a huge volume of water located between 300 and 600 meters depth from the Peruvian shores, is a natural phenomenon resulting from the interaction of the ocean currents and the biological productivity. But not all the hypoxia cases have a natural explanation. It is known that there exist other cases which are caused by human activity, such as in the Baltic or the Adriatic Sea. By all means, hypoxia always happens in quiet areas under organic matter-rich surfaces. It is precisely this large biological mass that, when it decomposes, makes a large number of bacteria to use dissolved oxygen from the water to feed, consuming practically all of it.
On the Balearic Islands coast there are no permanent and natural hypoxia areas, as the one studied in Peru. But sporadic hypoxia episodes happen, as for example the one happened in Portocolom (Manacor) in 2010.
The study warns of the growth in the proportion of poor oxygen areas into the planet waters and the need to track and analyze them, to foresee the consequences that can result in long-term on issues such as biodiversity and species disappearance. The result of this research show that, from now on, eddies must be taken into account in future analysis on the Peruvian coast and in all other places.
Agencia iberoamericana para la difusió de la ciencia y la tecnología
