Hi, this is Emily, from MinuteEarth.

Penguins like the cold - they're built for it, and most live in the cold waters near Antarctica.

But over 4000 miles north, in the tropical Galapagos Islands, you can also find penguins,

because of something called the Cromwell Current.

This cold-water current flows from west to east at about a hundred meters below the ocean surface,

until it collides with the underwater part of the Galapagos islands and turns upward towards the surface.

The current helps the penguins stay cool, but even more importantly, it helps them eat.

That's because it brings together nutrients and sunlight, the key ingredients that make green algae thrive, which allows penguins' food to thrive too.

Across most of the ocean, there's a sort of cruel separation between these ingredients, because sunlight only penetrates the top layer of water, while nutrients sink.

What's more, because the sun-warmed surface waters are less dense than the colder waters below, the two layers don't easily mix.

It takes winds or a current to bring the nutrient-rich waters up to the sunlit surface.

So, the ocean is like a salad dressing, where the denser vinegar stays trapped below the oil until you shake it up.

Where the ocean doesn't get shaken up, both green algae and the critters that eat it are relatively sparse.

But where it mixes, like at the Galapagos Islands, algae and the rest of the food chain can thrive.

Of course, penguins are more common in colder climates, partly because icy surface waters mix more readily with cold, nutrient-rich waters below.

But the world's cold, northern oceans don't have any penguins, because these flightless birds evolved in the South,

and it seems that although changes in climate over time may have helped them migrate northwards, there's simply too much warm, nutrient-poor water between them and the Arctic.

In fact, the world's only northern penguins are the Galapagos penguins that live at the tip of Isabela Island, just a hair – or a feather – above the equator.

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