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Place 05 · The Southern Ocean · Chapter 3 of 7
The Current That Never Hits Land
Around Antarctica runs a current carrying more than 100 times the flow of all the world’s rivers combined, and it never has to turn around.
About 15 minutes · 1 video · 1 live current map · 2 quick activities
Start here
A ring with no walls
Everywhere else, ocean currents run into continents and get bent back into giant loops called gyres. In the far south there is a band of latitudes with no land all the way around the planet, so the westerly winds can push the water around Antarctica, west to east, without end. The one tight squeeze is Drake Passage, the roughly 800 km gap between South America and the Antarctic Peninsula.
Watch this
See it move
SOCCOM Project — Deep Dive: Antarctic Circumpolar Current. A whirlwind tour, in under four minutes, of the biggest current on the planet, from a research project that sends robot floats into the Southern Ocean.
While you watch, look for
- What pushes the current around Antarctica, and which way it flows
- Why nothing ever gets in its way
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The wind
Roaring, furious, screaming
Sailors named the westerly winds of the far south by latitude: the Roaring Forties, the Furious Fifties and the Screaming Sixties. From about 40°S to the Antarctic Circle blow the strongest average winds on Earth, with hardly any land to slow them down. They drag the surface water eastward, and that endless drag keeps the whole current turning.
The size
Measured in sverdrups
Ocean currents are measured in sverdrups: 1 Sv is a million cubic meters of water every second, and all the rivers on Earth together add up to only about 1 Sv. Instruments moored across Drake Passage from 2007 to 2011 measured the Antarctic Circumpolar Current at about 173 Sv, 30% more than the textbook figure used before. It reaches from the surface to about 4,000 m down and runs about 21,000 km around the continent.
The border
The Polar Front
Inside the current runs the Polar Front, also called the Antarctic Convergence, where cold Antarctic surface water meets warmer water from the north and sinks beneath it. Cross it and the sea gets noticeably colder, and the wildlife changes: many birds, fish and other animals typical of Antarctic water are rare on the other side. The current and its fronts wall Antarctica off from warmer water, which helps keep it frozen.
Photos: Rachel Claire, Diego F. Parra, Nancy B. / Pexels
Play with it
Watch the current go around
This live map shows today’s ocean surface currents, seen from above the South Pole. Look for the ring of fast flow circling Antarctica from west to east, which looks clockwise from up here, then drag the globe until you find Drake Passage below the tip of South America.
Live map: earth.nullschool.net by Cameron Beccario, ocean currents from OSCAR (Earth & Space Research) and the Copernicus Marine Service.
Two questions to answer while you are in there
- Where around Antarctica does the flow look fastest and most tightly squeezed? Is that where South America comes closest?
- Follow one streak of flow as far as you can. Does it ever run into a coastline and turn back, the way currents in the other oceans do?
Try it yourself
Check yourself
Try it
True of the Current
Click every word that is true of the Antarctic Circumpolar Current, and leave the myths alone.
Try it · interactive
Circumpolar Current
Turn up the westerlies over a map of the Southern Ocean and watch the current speed up, read its flow in sverdrups, then close and reopen Drake Passage to see why only an unbroken ring of ocean lets a current circle the globe.
Open the Circumpolar Current in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Antarctic Circumpolar Current
Eastward current circling Antarctica; the world's largest
Sverdrup
One million cubic meters of water per second
Westerlies
Winds blowing from west to east at midlatitudes
Polar Front
Boundary where cold Antarctic water meets warmer water
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: The Current That Never Hits Land
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Our World Ocean 10.4 — Polar Ocean Currents — LibreTexts · 5 minutes
- Oceanography 101 (MiraCosta) 9.8 — The Gulf Stream and the Antarctic Circumpolar Currents — LibreTexts · 4 minutes
- The Conversation — Explainer: how the Antarctic Circumpolar Current helps keep Antarctica frozen — The Conversation · 6 minutes
Photo credits (Pexels): vasu jamwal, Jan Tang, Rachel Claire, Diego F. Parra, Nancy B..