Ten ocean facts the source pages back up

The physical ocean is where the library keeps its most forwarded facts: sound that crosses basins, a waterfall taller than any on land, a sea that dried out. These are ten oceanography facts with sources attached. I read each source page, copied the sentence that carries the claim, and noted the one figure the source puts differently. [1]

The ocean library has more than these ten. I picked the ones about water, sound and the seafloor rather than the animals, which deserve their own list.

Sound in the sea

Sound moves four times faster underwater

The Wikipedia article on underwater acoustics gives the numbers: "Approximate values for fresh water and seawater, respectively, at atmospheric pressure are 1450 and 1500 m/s for the sound speed" [1]. The speed of sound in air at 20 degrees is about 343 metres a second, so seawater is a little over four times faster [2]. The fact page rounds that to four, which is fair.

Why it matters: it is the reason whales can be heard across an ocean basin, and the reason sonar works at all. The same article notes that the speed rises with pressure, temperature and salinity, so the ocean is not one medium but a stack of them [1].

A layer a kilometre down traps sound

The stack has a floor. Around a kilometre down, falling temperature and rising pressure combine to make a layer where sound travels slowest, and a sound wave that enters it bends back towards the middle instead of escaping. That is the SOFAR channel, and a low call that enters it can cross thousands of miles before it fades. Navies built listening networks on it in the Cold War, and fin whales appear to use it to sing to each other at long range.

The maps

We have better maps of Mars than of the seafloor

The seafloor-mapping article says it plainly: "the ocean seabed in many locations is less mapped than the topography of Mars" [3]. The reason is in the method. Radar from orbit scans a whole dry planet; sonar has to be dragged across the sea, boat by boat. The library fact says the same thing in two lines.

Most of the seafloor has never been seen

There is a difference between mapped and seen. NOAA's ocean exploration page says the whole seafloor has been mapped from satellites at coarse resolution, but that "explorers have seen less than 0.001% of the deep ocean seafloor" [4]. The library's companion fact puts the detailed sonar coverage at about a quarter, which is the figure the GEBCO project tracks. Three numbers, three meanings: seen, surveyed by ship, and guessed from gravity.

Water on the move

The Atlantic conveyor keeps Europe out of Siberia

The library's version is blunt: one ocean current is the reason Europe is not Siberia. The current is the Atlantic meridional overturning circulation, which carries warm surface water north and returns cold water at depth. I have not quoted its source page here, so this entry carries no number of its own. The library fact is the vivid version of a plain one: the current warms northern and western Europe, and the Siberia comparison is what that warming is worth. It stays on the list for the mechanism, which the other nine facts depend on too.

There is a waterfall in the ocean taller than any on land

Cold, dense water from the Nordic seas pours over a ridge between Iceland and Greenland and sinks into the deep Atlantic. Wikipedia's article on the Denmark Strait cataract says "the Denmark Strait overflow would be the tallest waterfall in the world were it on land" [5]. The water falls over 3.5 kilometres, more than three times the height of Angel Falls, and the flow is around 3.2 million cubic metres a second [5]. The fact page calls it two miles, which matches.

The Mediterranean dried out, then refilled

About 5.33 million years ago the Mediterranean was a basin of salt flats, cut off from the Atlantic. Then the Atlantic broke through at Gibraltar. The library says the basin may have refilled in a couple of years. The Zanclean flood article is more cautious: "Complete refilling of the Mediterranean may have taken about a decade." [6] It also notes the refilling may have come in several pulses. So the flood is real and fast by geological standards, but a decade is the better figure, and I would read the library's two years as the lower end of the models.

Scale

The longest mountain range on Earth is underwater

The mid-ocean ridge system runs through every ocean. Its article says "The continuous mountain range is 65,000 km (40,400 mi) long" [7], several times the length of the Andes, with the whole ridge system at about 80,000 kilometres [7]. The library fact gives 40,000 miles, which is the same number in different units.

The most abundant photosynthesiser was found in 1986

Prochlorococcus is a cyanobacterium so small it slipped through the filters oceanographers had used for a century. Its article says these bacteria "are probably the most abundant photosynthetic organism on Earth" [8] and dates the discovery to 1986, by Sallie Chisholm's group [8]. The fact page has the short version.

There is enough salt in the sea to bury every continent

The library says that if you dried out the oceans you could spread the salt 150 metres deep over all the land. I have not re-derived that figure for this post, so I am listing it as the library states it rather than as something I checked, and the fact page carries its source.

Questions

Which of these ocean facts has the weakest source?

The salt figure. The library says the sea holds enough salt to cover every continent to a depth of 150 metres, and I did not re-derive it from the seawater article for this post. The Mediterranean refill is the other soft spot: the Zanclean flood article says about a decade where the library says a couple of years [6].

How much of the ocean floor has actually been mapped?

It depends on what you count. NOAA says the whole seafloor has been mapped from satellites at coarse resolution, while explorers have seen less than 0.001% of the deep seafloor with their own instruments [4]. Ship-based sonar at useful detail covers about a quarter, which is the share the library's GEBCO fact reports.

How fast does sound travel in seawater compared with air?

About 1,500 metres a second in seawater at the surface, against about 343 metres a second in air at 20 degrees [1] [2]. That is a ratio of roughly 4.4, which the library rounds to four. The speed in water rises with pressure, temperature and salinity, so it changes with depth and season [1].