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  • Writer's pictureIanna Luna

Where are the shearwaters?

Yesterday as I crashed into sleep, during the last conscious seconds, my charger looked like a tube and silver water went through it. I just accepted it as I drifted into silent darkness.

The filtering system that messes up my conception of reality.

Later, when I was up again and wouldn't have accepted as easily that my charger was filtering water through the wall, I crouched beside the Niskin bottle and poured a bit of water into a sampling bottle, but something felt different. The water wasn't nearly as cold as in earlier days when we cruised through Nublo, a cyclonic, cold core eddy.

When our shift was done, Álvaro, Aja and I found a spot on deck to relax on for a few minutes. Somehow, Javier knew how to find us. He had a strange look on his face, a pensive look, as he looked at the horizon and back at our expectant faces. "Have you noticed there aren't any shearwaters?" he asked, smirking.

There wasn't one in sight.

As we stared on, maybe one or two appeared, but the poor things were either lost or unlucky. This meant we had arrived at Anaga, our anticyclonic eddy. These kind of eddies suck surface water into the deep through a process called downwelling, burying nutrients deep in the water column, turning themselves into productivity deserts. Less primary production means zooplankton will have less food, and so will the fish, so... there's no food for the shearwaters here.

Jelly critters from Anaga fished with our zooplankton net.

Cyclonic eddies are a different story. These bring nutrient-rich cold waters to the surface through a process called upwelling, increasing productivity, and therefore, life abundance.

Effect of (a) a cyclonic and (b) an anticyclonic wind on the surface of the ocean in the Northern Hemisphere. Taken from The Open University course The Oceans.

Eddy dynamics are intrinsically related to the richness of biological communities. At the warm core of Anaga all we could find were jelly creatures, debris and plastic. But Nublo? What an explosion of life. Our filters were screaming ENOUGH! I mean... look at that burst of chlorophyll:

Chlorophyll satellite image of our eddies. From: Copernicus.

As our shift ends, the sun peeks from behind the clouds like a shiny egg yolk. The night is gone as we reach one of the last of our sampling stations: Garajonay is upon us!

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