Massive plankton blooms are the plague of the oceans. They starve local species by exhausting an ocean of its food and oxygen, they turn vast areas of sea to the colour of milk and have a profound effect on the ocean food web.

But where do they come from? Nobody knows. At least they didn’t until Mathias Sandulescu and buddies from Carl-von-Ossietzky Universitat in Oldenburg Germany, started hunting for the origin. And they reckon they’ve found it.

Plankton blooms, it turns out, are born in the wake vortices that form downstream of islands. But there’s a caveat: the blooms only form in certain circumstances.

Sandulescu says that the essential extra factor is an upwelling of nutrient rich waters upstream of the islands and has tested the idea using mathematical models of the ocean currents around the Canary Islands off the coast of Africa.

The model shows how nutrients become trapped in the downstream vortices and provide a steady source food on which the plankton feast as they bloom. When the bloom gets large enough, it escapes from the vortex and heads out into open water.

Of course, this is a perfectly normal process. Most blooms never get to the size of small countries and never wipe out entire ecosystems of ocean life.But now we know where they come from, it may be possible to monitor their production and the way in which they grow after their birth.

Ref: arxiv.org/abs/0802.3532: Biological Activity in the Wake of an Island Close to a Coastal Upwelling

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