The crazy richness of the Humboldt sea current, at the origin of a miraculous fishery now threatened

2023-08-21 19:00:00
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It is neither the strongest nor the widest of ocean currents. Even less one of those fundamental pulsations that punctuate the life of our planet, like the famous Gulf Stream. “Frankly, the impact of the Humboldt current on the global climate is not very importantagree oceanographers and climatologists François Colas and Vincent Echevin. It would disappear – which will probably not happen – that the major physical balances would not be upset. » Suffice to say that one might wonder what this 50 to 200 kilometer wide strip of cold water that borders the western coast of South America is doing in a series of articles devoted to the deep breathing of the planet. Except that researchers from the Research Institute for Development (IRD) continue: “On the other hand, its impact on the ecological, biological and economic level is major, essential for South America, but, more broadly, for the world. »

We have been warned. With the Humboldt current, we enter not a land of contrasts, but of paradoxes and exceptions. Its origin, its operation, its consequences, its very name make it a phenomenon apart. The case seems settled: a powerful flow of cold water from Antarctica would run along the Pacific coast for 5,000 kilometres, boosting the ocean food chain to the point of having enabled the construction since the middle of the 20th century of the industrial fishery most productive in the world, from Chile to Peru.

This overview of the phenomenon can still be found today in a number of works intended for the general public. However, it is both incomplete on its consequences and false on its causes. Humans did not wait until the 1950s and the second agricultural revolution to understand what they could get from the exceptional natural resources of this region. From their arrival on the continent, at least fourteen thousand years ago, to the guano collectors of the 19th century, passing through the first real cities erected more than five thousand years ago and even to the Incas, who nevertheless settled in the mountains. , some 200 kilometers from the coast, the history of the presence of sapiens in this part of the new world was in reality, we will come back to it, shaped by the ocean.

« Molle » circulation

But let’s first rectify the main error in our short definition: a powerful current of cold water from Antarctica. Well no ! First the circulation observed along the east coast « molle », insists François Colas: a few centimeters per second, where the Gulf Stream pushes water at more than 1 meter per second. Above all, the cold water does not come from the south but… from the bottom. In their laboratory on the Jussieu campus in Paris, François Colas and Vincent Echevin explain, with supporting drawings, the sequence of phenomena. First, there is the wind, which turns counter-clockwise around the huge anticyclone installed in the middle of the South Pacific. On this side of the ocean, it therefore blows from south to north. It should push the water along the coast. Except he’s not alone. Added to this is the Coriolis force, created by the rotation of the Earth. All this leads to pushing the surface waters not towards the north but towards the open sea. And as it is necessary to balance the level of the sea, water rises from the depths. A slow movement, very slow even, of about 1 meter per day, but relentlessly.

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