Ocean and coastline facts
The ocean covers most of the planet and is measured far less precisely than the land. Even the length of a coastline has no single correct answer, which is a genuine mathematical property rather than a shortcoming of the survey.
Roughly how much of the ocean floor has been mapped in high resolution?
About a quarter
Around 25 percent of the seabed has been mapped to modern standards, a figure that has risen sharply since 2017 but still leaves most of the planet's surface unsurveyed in detail.
Source: Seabed 2030 project progress reports
What is unusual about the Sargasso Sea?
It has no coastline
Bounded by four ocean currents rather than land, it is the only sea defined without a shore. Eels from Europe and America both migrate there to spawn.
Source: NOAA Ocean Service; Sargasso Sea Commission
What is unusual about the deep water of the Black Sea?
It has almost no oxygen
Fresh river water floats above dense salt water from the Mediterranean and the layers barely mix. Below about 150 m there is no oxygen, which preserves shipwrecks remarkably well.
Source: Black Sea oceanographic surveys
Where are the world's largest tides?
The Bay of Fundy
Fundy, on Canada's Atlantic coast, has a tidal range reaching about 16 m. The bay's length and depth give it a natural resonance close to the tidal period, amplifying the range dramatically.
Source: Canadian Hydrographic Service
The Mediterranean is thought to have almost completely dried out. When?
About 5 to 6 million years ago
The Messinian salinity crisis: the Strait of Gibraltar closed and the sea evaporated, leaving kilometre-thick salt deposits. It refilled catastrophically when the Atlantic broke back through.
Source: Deep Sea Drilling Project cores; Messinian stratigraphy
The doldrums, feared by sailing ships, are what?
A belt of calm
The intertropical convergence zone, where trade winds from both hemispheres meet and rise, leaving little horizontal wind. Sailing ships could be becalmed there for weeks.
Source: Standard meteorology; historical navigation accounts
The Great Pacific Garbage Patch is best described as what?
A diffuse soup of plastic fragments
It is not a visible island. Most of it is fragments suspended near the surface across an area sometimes quoted as three times the size of France, at low concentration.
Source: The Ocean Cleanup surveys; NOAA Marine Debris Program
Rogue waves were dismissed as sailors' tales until when?
1995
The Draupner wave, a 26 m peak measured by a laser instrument on a North Sea platform on New Year's Day 1995, confirmed that waves far larger than surrounding seas genuinely occur.
Source: Draupner platform instrument records, 1 January 1995