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Where the tides turn

Amphidromic points

How high does the high tide go? In the Bay of Fundy, Canada, the difference between high and low tides is more than 16 metres. But at several points in the world’s oceans, called the tidal nodes, the sea level doesn’t change at all.

Largest ocean current

Southern Ocean

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.

Underwater unknown

Paleodictyon

A strange honeycomb pattern appears on sea ridges around the world. We think that it is created by living creatures, but no-one has ever seen one. Oh, and there are fossils of the patterns going back 500 million years.

Saltiest ponds

Don Juan Pond

We’ve all heard of the Dead Sea, so salty that people naturally float in it. But the Gaet’ale Pond in Ethiopia is saltier, and the Don Juan Pond in Antarctica is so salty that it doesn’t freeze, even at -50°C.

The world wonders

Samar

In World War II, it was standard practice to add nonsense phrases to coded messages in transit, in order to thwart decryption efforts. One of those phrases accidentally changed the course of the largest naval battle in history.