01 A current that lifts water

The Benguela Current flows northwards and forms the eastern part of the South Atlantic gyre. It runs from Cape Point to roughly 16 degrees south, and measures between 200 and 300 kilometres wide. Upwelling pulses propagate southwards along the coast at speeds of 5 to 8 metres per second.

And the effect on land is the one you notice the moment you look at the landscape: the cold current decisively influences the climate of Angola and Namibia, and contributes to the coast's aridity. It is why Luanda, less than nine degrees from the equator, receives 405 millimetres of rain a year.

Natural-colour satellite image of the south-west African coast: on the left the ocean in very dark blue with threads and swirls of pale turquoise green curling close to the shore; on the right, the land in sand, ochre and muted green tones, with a large patch of pale dunes beside the coast and scattered white clouds over the sea.
The green swirls hugging the coast are phytoplankton. It is the upwelling made visible from space.MODIS Land Rapid Response Team, NASA GSFC / Wikimedia Commons / dominio público·Dominio público

02 The productivity figure

Deep water is nutrient-rich because everything that sinks accumulates down there. When that water rises into the surface layer, where light penetrates, the phytoplankton has both things it needs at once: food and sun. And it explodes.

The Benguela system's annual biomass production is 4.7×10¹³ grams of carbon a year: between 30 and 65 times the global ocean average per unit area.

That range is worth pausing on. It is not that this sea is somewhat better than average: it produces an order of magnitude more, and at the top of the range almost two. The whole chain that follows — the fish, the birds, the marine mammals — rests on that figure.

Another satellite image of the same coast: the ocean fills the left half in deep navy, with a diffuse cloud of pale green spread in front of the shore; on the right, the land shows a continuous band of orange sand along the sea and, inland, a mosaic of brown and green tones with white clouds in the corners.
The contrast that defines this coast: desert on land and an explosion of life in the water, a few kilometres apart.MODIS Land Rapid Response Team, NASA GSFC / Wikimedia Commons / dominio público·Dominio público

03 The pilchard and the 1968 peak

Historically the system's fishery was dominated by pilchard of the genus Sardinops. Its peak came in 1968, with over 1.3 million tonnes taken in a single year. Today the dominant species in the catch is the anchovy, Engraulis capensis.

That shift from one species to another is the part of the story worth reading slowly. A fishery that goes from pilchard to anchovy has not changed its taste: it is an ecosystem that has changed state. And the peak of 1.3 million tonnes is, seen from here, more a warning than a record.

04 The year it fails

Roughly once a decade what is known as the Benguela Niño occurs: warm, nutrient-poor water from the Angola Current intrudes into the system and creates conditions similar to those of the Pacific El Niño.

When that happens the engine switches off: without cold water there are no nutrients, without nutrients no phytoplankton, and without phytoplankton none of what comes after. A coast that depends on an upwelling also depends on that upwelling not being interrupted.

Aerial view of the Bay of Luanda with the water in turquoise and blue-green tones filling the left half; the coastal avenue curves sharply between the water and the city, and to the right glass office towers and low blocks pile up to the horizon, with an ochre-walled fortress on a rise in the foreground.
The city and its bay. The colour of the water is not tropical: it is that of a cold current loaded with life.Délcio Geovany Borges / Wikimedia Commons / CC BY 4.0·CC BY 4.0

It is worth keeping in mind when you sit down to eat fish on the Ilha. What is on the plate does not come from any ordinary tropical sea: it comes from one of the most productive upwelling systems on the planet, and from a belt of cold water that is also the reason not a drop falls in June and July.

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Lucía Montes

Worth Knowing editor · Flowtravel

Lucía chases the story behind the everyday object.

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