MAY 2009

A WHALE OF AN OCEANBY STEPHEN WHITT

But what makes these waters in the Antarctic so special that they were once home to such a huge concentration of the largest animals on Earth? There are two explanations. One is that the Earth is tilted, and the other is that cold water sinks.

Most places on Earth have regular cycles of day and night all year. At the North and South Poles, however, the tilt of the Earth means that each pole has both days and nights that last for months. In the Antarctic summer there is plenty of sunlight for the phytoplankton to make their food. But there is sunlight elsewhere, too. What else makes the Southern Ocean special? The answer is cold water.

Water is a little like air. Just as warmer air will rise above cooler air (think of a hot air balloon), warmer water rises above cooler water. In the tropics, where the Sun heats the water by day, warm water stays at the surface, while the colder water remains below.

In that deep water are nutrients that could help phytoplankton grow. But there is no sunlight there. The phytoplankton cannot grow. At the surface, there’s plenty of sunlight, but few nutrients. What’s a phytoplankton to do?

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http://beyondpenguins.nsdl.org

ABOUT THE AUTHOR

Stephen Whitt

Director of Experience Programs Teaching and Learning COSI

Supported by the National Science

Foundation

Licensed Under a Creative Commons license.

http://creativecommons.org/licenses/by-sa/3.0/

Find this story and others at:

http://beyondpenguins.nsdl.org/information.php?topic=storiesFlesch - Kincaid RL = 4.7

Issue 14: Polar Oceans (May 2009)Copyright May 2009 – The Ohio State University

Stephen Whitt has been with COSI since 1993, performing shows and demonstrations, writing exhibit signs and show scripts, and co-directing COSI’s f loor faculty. He has written over 40 articles for children’s science magazines, and his first book, called The Turtle and the Universe was published by Prometheus Books in 2008.

A WHALE OF AN OCEANA WHALE OF AN OCEAN

A WHALE OF AN OCEANA WHALE OF AN OCEAN

Krill eat tiny living things called phytoplankton. Phytoplankton float at the surface of the Southern Ocean. They use the energy of sunlight to make food. The krill eat the phytoplankton, and the blue whales eat the krill. It’s one of the simplest food chains on Earth.

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GLOSSARY

BALEEN – stif f, f lexible bristles inside a whale’s mouth

KRILL – small, shrimplike animals that live in the ocean

PHYTOPLANKTON – small f loating plants

Photo courtesy of T. Bjornstad, Wikimedia Commons

Plankton magnified.Blue whales eat krill. Krill eat phytoplankton. This is a simple food chain

Krill

Blue Whale

Phytoplankton

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A WHALE OF AN OCEANA WHALE OF AN OCEAN

Blue whales are known as baleen whales. Instead of teeth, baleen whales have f lexible bristles (called baleen) in their mouths. They use these bristles like a spaghetti strainer. When blue whales find a large school of krill, they gulp enormous mouthfuls of krill and water, then push the water back out with their tongues. The baleen traps the krill inside, just as a spaghetti strainer traps noodles. The whale then swallows the krill. Yum!

In the warm waters off the coast of Africa, a blue whale has just given birth. The baby is already twenty-six feet long and weighs six thousand pounds. She grows around eight pounds every hour. The mother weighs as much as twenty elephants. Yet she is starving.

The Southern Ocean is dif ferent. It doesn’t get as hot as the tropics. So even though there’s a lot of sunlight, the water doesn’t get warm. The cold water from the surface sinks down, pushing the deeper, nutrient-rich water back up. This means there are both lots of sunlight and lots of nutrients in the same place. With plentiful sunlight and plentiful nutrients, the phytoplankton grow like crazy! The krill population explodes. The whales come to feast.

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Baleen from a whale’s mouth. Photo courtesy of drgf lyorng, Flickr.

Photo courtesy of Jason Armstrong, Flickr.

Why doesn’t the mother blue whale grab a quick snack? Quite simply, there is no food for her here. She will survive on her thick coat of blubber. In a few months, she will take her calf to their feeding grounds at the bottom of the world, the Southern Ocean that surrounds Antarctica.

Before whale hunting nearly wiped them out, there were well over two hundred thousand blue whales living off Antarctica. By the time the slaughter stopped, there were fewer than a thousand left.

Why would any animal seek out the cold waters at the bottom of the world? The answer is simple: food. Blue whales are the largest animals on Earth. Yet they are adapted to eat just one kind of prey. That prey is a two-inch long animal called krill.

Or they once did. In the days before whaling, the Southern Ocean was alive with great whales. Some approached one hundred feet in length. In a single generation, human beings hunted these giant animals to the very edge of extinction. Today, while the blue whale is protected from hunters, its numbers remain low. A blue whale mother has just one calf every two to three years. At that rate, it will take many years for the blue whales to recover. But in time, perhaps, the whales in their thousands will again dine on krill in their millions at the bottom of the world.

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A WHALE OF AN OCEANA WHALE OF AN OCEAN

A WHALE OF AN OCEANA WHALE OF AN OCEAN

Whales eat krill. Photo courtesy of Wikipedia.

Antarctica and the oceans that surround it.

Photo courtesy of Seabass London, Flickr.

SOUTHAMERICA

ANTARCTICA

AFRICA

AUSTRALIA

ASIA

PACIFICOCEAN

ATLANTICOCEAN

SOUTHERNOCEANINDIAN

OCEAN

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