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The Ocean in Seven Places · Place 05
The Southern Ocean
When seawater freezes, the salt is left behind, and that single fact drives the circulation of every ocean on Earth. It starts here, around Antarctica.
Seven short chapters · about 15 minutes each · a practice set at the end of every chapter
Start here
What you are walking into
Seven short chapters. Each one has a video, a few pictures, something to play with and a quick activity, and very little reading. The first four follow the water itself: how seawater freezes and throws its salt away, why the heavy water left behind sinks to the bottom of the world, the current that circles Antarctica without ever touching land, and the wind that builds some of the biggest waves on Earth. That bottom water is the same cold water you just met filling the deep basins of Place 04.
The last three are about what lives here and what melts here. Cold water soaks up carbon dioxide, the gas behind the ocean acidification you met on the reef in Place 01. A food chain with just three links feeds the biggest animal that has ever lived. And the ice on Antarctica, up to about 4.8 km thick, will help decide where the world’s coastlines are in 2100. By the end you will understand the engine room of the world ocean. You will also have picked up a fair amount of physical oceanography. Nobody has to know.
Before you start
Watch this first
Luke Maximo Bell — ANTARCTICA: The Frozen Continent. Three minutes of drone footage over the ice. No notes, no questions. Just get cold.
And then this: the currents, from above
NCI Australia — Circulation of the Southern Ocean. Four minutes of a supercomputer model of the currents swirling around Antarctica, made with Dr Andy Hogg’s team at the Australian National University. Watch the eddies; they never stop.
The seven chapters
Your route around the bottom of the world
Chapter 1
When Seawater Freezes
Seawater freezes at about −1.8 °C and throws most of its salt away. Every winter it does this over an area bigger than Antarctica.
Chapter 2
The Water That Sinks
Cold, salty water is heavy water. Some of it sinks off Antarctica and spends centuries creeping along the bottom of the world.
Chapter 3
The Current That Never Hits Land
Nothing gets in its way: the biggest current on Earth carries about 173 million cubic meters of water a second, all the way around the planet.
Chapter 4
The Biggest Waves on Earth
With no land to stop them, the westerlies build waves as tall as an eight-story building, and send their swell all the way to California.
Chapter 5
Cold Water Holds More
Cold water holds more gas. That is why about 40% of the carbon dioxide humans have added to the ocean went in down here.
Chapter 6
The Shortest Food Chain in the Sea
Diatoms, krill, whale. The biggest animal that has ever lived is only three links away from the Sun.
Chapter 7
The Ice That Decides the Coastline
Antarctica holds enough ice to raise the seas by about 58 m. Whether that ice floats or sits on rock makes all the difference.
Photos: Igor Dudkovskiy, Jonathan Cooper, vasu jamwal, Magda Ehlers, David Kanigan, Silvana Palacios, Francesco Ungaro / Pexels
Play with it
Visit a ship the ice ate
In 1915 Ernest Shackleton’s ship Endurance was trapped, squeezed and finally crushed by pack ice in the Weddell Sea; the crew escaped across the ice and every one of them survived. In March 2022 an expedition found the wreck 3,008 m down, upright and in remarkable condition. This 3D model was built from images released after the discovery: spin it, and look for the ship’s wheel and the name on the stern.
3D model: “Endurance Ship Wreck discovered” by Simeon Schmauß on Sketchfab (CC BY), built from images by the Falklands Maritime Heritage Trust / National Geographic.
How to use these pages
Watch it, read it, try it
Every chapter has the same rhythm: a video, three short cards, something live to explore, and a couple of hands-on activities. The last activity on each page is an eight-question practice set that covers the whole chapter. Do every one, retry anything you miss, and read the feedback. The wrap-up page ends with a twenty-question review of the whole Southern Ocean.
Warm-up
What do you already know?
Six true-or-false guesses before you start. Getting some wrong right now is the point: each answer tells you which chapter explains it.
Ready?
Chapter 1 is fifteen minutes and mostly pictures
Photo credits (Pexels): Francesco Ungaro, Markku Soini, Igor Dudkovskiy, Jonathan Cooper, vasu jamwal, Magda Ehlers, David Kanigan, Silvana Palacios.