How do you measure ocean flow? One sverdrup equals a million cubic metres of water per second. All of the world’s rivers emptying into the ocean is 1.2 sverdrups; the largest current in the world is more than a hundred times larger.
The usual way to measure water flow is in cubic metres per second. This works fine to measure rivers: the Amazon clocks in at 290,000 m3s-1, for example, which is equivalent to more than 80 Olympic-sized swimming pools every second. It’s also larger than the flow of the next largest seven rivers combined.
It gets a bit trickier when it comes to oceans. Unless you want to employ a lot of zeroes and a lot of commas, it’s useful to have a unit of measurement that’s a bit bigger. 1,000,000 cubic metres of water per second equals one sverdrup. It’s a unit named after Harald Sverdrup, a Norwegian oceanographer. (He’s also the namesake of the Sverdrup balance, an important precursor to our understanding of global ocean flow.)
The discharge of the Amazon River into the ocean equals 0.29 sverdrups. All of the rivers in the world together are 1.2 sverdrups. The Gulf Stream, one of the more significant ocean currents for humans, begins at around 30 sverdrups – the equivalent of 30,000,000 cubic metres of water every second. It ends much higher, but it’s still not the biggest ocean current in the world.
The Antarctic Circumpolar Current sweeps all around the continent of Antarctica, propelled by wind and unimpeded by land. It connects all the other major oceans together and actually keeps Antarctica cold and isolated by pushing warmer waters around it rather than into it. This current is at least 150 sverdrups, making it the largest in the world.
(An end note: the refilling of the Mediterranean was equal to 100 sverdrups, and that took less than two years.)