- Javier Arístegui
Eddies in the Canary Islands: a Gaia perspective
We have been studying the eddies of the Canary Islands for more than 30 years, and during this time we have discovered many of their secrets. For example, that they are formed in the lee of the islands due to the disturbance of the flow of the Canary Current, producing cyclonic and anticyclonic “vortex streets”, which are released alternately – in some cases, such as in the south of Gran Canaria, with almost perfect symmetry – what is known in fluid dynamics as a “Von Kármán vortex street”. The cyclonic and anticyclonic eddies operate like a two-way pump, intensified by the effects of wind stress: the first, pumping nutrient-rich deep water into their centers, increasing plankton productivity, the latter, sinking organic matter to the bottom. The fronts between eddy pairs are regions of convergence where live, and inert, materials accumulate and can be transported by different mechanisms towards the deep ocean.
We know that eddies can connect with each other, exchanging water of different temperature and productivity; some even interacting with the productive waters of the African coastal upwelling, inducing the development of filaments of enriched waters that may reach the eastern islands. We also know that the eddies that detached off the islands months ago have undergone a metamorphosis in their structure and present physical processes that are very different from those that regulated their dynamics when they originated. What we still do not know is how these processes have evolved throughout the life history of the eddies, and this is part of what we want to study in the e-IMPACT project. We also want to find out what role eddies play in carbon sequestration in the deep ocean throughout its lifetime, in order to be able to extrapolate these processes to other ocean regions and see their impact at a global scale.
In this search for new secrets about the Canary eddies, we have embarked on our first project cruise, researchers and undergraduate and master's students from the University of Las Palmas de Gran Canaria (ULPGC), as well as scientists from the Spanish Research Council (CSIC). We have been studying three eddies for a month in their genesis processes, which we have named Nublo (in the south of Gran Canaria), Anaga (in the south of Tenerife) and Garajonay (between La Gomera and El Hierro). In four months we will study these same "mature" eddies, which will have travelled hundreds of miles along the so-called "Canary Eddy Corridor" and hopefully we will know how they have evolved throughout their life cycle. This journey into the unknown would not be possible without the support of high-resolution satellite images and models from the Copernicus service, as well as an underwater robot (glider) operated by the Canarian Oceanic Platform (PLOCAN).
The Canary eddies, however, do not function as isolated systems, they constitute a "circulatory system" with a multitude of hearts that pulsate with greater or lesser intensity in both directions, and which are connected by "arteries" to each other, exchanging heat, energy and biogeochemical properties. Some of these "hearts", such as Garajonay, beat with immense intensity at a fixed place, enriching the channels between some islands, like El Hierro, La Gomera and Tenerife, fading over time, until they are activated again. Other “hearts”, such as Nublo and Anaga, will drift towards the open ocean transporting their productivity and fertilizing more distant waters. All this circulatory system is in some way connected with the waters of the African coast, reminding us of the origin of the first inhabitants of the Canary Islands. It forms like a small Gaia, as our recently deceased James Lovelock would say, a nerve center of productivity, which gives meaning to the balance and fertility of the islands and their connection with the rest of the subtropical Atlantic Ocean.
To the left, the eddy corridor south of the islands. To the right, the Gaia connection.