Is There a Lake at the Bottom of the Ocean?
The short answer
Yes. About 1,000 m (3,300 ft) down in the Gulf of Mexico there's a small lake of brine on the sea floor. Scientists nicknamed it the Jacuzzi of Despair. It's about 30 m (100 ft) around, and its water is up to about three times saltier than the sea around it.
Brine that salty is heavier than seawater and barely mixes with it. So it pools on the sea floor like a lake, with its own surface and shoreline. This one fills a crater whose rim stands about 3 m (10 ft) above the sea floor, and brine spills over one side like a waterfall.
Where the salt comes from
In the Middle Jurassic, the Gulf of Mexico was a shallow sea. It was cut off from the world ocean and dried out, leaving thick layers of salt. That salt was laid down more than 160 million years ago, and it is now buried deep under the sea floor.
Water moving through the sediment dissolves the buried salt and seeps back up as brine. The Gulf has brine lakes as small as 1 m across and as long as 20 km. Brine is so heavy that a small submarine, the Johnson Sea Link, once floated on top of one of them, like a boat on a pond.
What's in the pool
The top 3 m of brine measured 80 to 110 on the salinity scale. Average seawater is about 35, so the brine is roughly 2 to 3 times saltier. The pool is saturated with methane, and bubbles were seen rising from two spots in it.
Below the brine is dense, soupy mud full of hydrocarbons. A sampling line went about 19 m (62 ft) into the pool and never reached a hard bottom. Oxygen was not reported for this pool, but deep brine pools studied elsewhere have almost none.
Deadly, but not hot
The salty brine can be fatal to many animals that fall in. The explorers saw dead crabs and large isopods preserved along the edge. That is the scientists' wording: many animals, not everything that enters. In brine pools in the Red Sea, an eel was seen dipping into the brine again and again, probably to grab animals the brine had stunned or killed.
The nickname refers to the pool's warm temperature of 19 °C (66 °F), but that reading came from the mud under the brine. The brine itself measured about 8 °C (46 °F). Both are far cooler than a real hot tub.
Key numbers
| What | Number | Source |
|---|---|---|
| Depth of the Jacuzzi of Despair | about 1,000 m (nearly 3,300 ft) | Ocean Exploration Trust, 2015 |
| Distance around the pool | about 30 m (100 ft) | Ocean Exploration Trust, 2015 |
| Height of the crater rim above the surrounding sea floor | 3 m (about 10 ft) | Cordes et al. 2016, Oceanography 29(1) supplement |
| Thickness of the brine layer, above the soupy mud | about 3 m | Cordes et al. 2016, Oceanography 29(1) supplement |
| Salinity of the top brine layer | 80 to 110 psu | Cordes et al. 2016, Oceanography 29(1) supplement |
| Average salinity of seawater | about 35 parts per thousand | NOAA Ocean Service, Why Is the Ocean Salty? |
| How much saltier the brine is than average seawater | roughly 2 to 3 times | Our arithmetic from Cordes et al. 2016, Oceanography 29(1) supplement and NOAA Ocean Service, Why Is the Ocean Salty? |
| Temperature of the brine | 7.8 °C (46 °F) | Cordes et al. 2016, Oceanography 29(1) supplement |
| Temperature of the mud under the brine | 19 °C (66 °F) | Cordes et al. 2016, Oceanography 29(1) supplement |
| How far a sampling line went into the pool without reaching a hard bottom | about 19 m (62 ft) | Cordes et al. 2016, Oceanography 29(1) supplement |
| Age of the buried Gulf of Mexico salt | more than 160 million years | Hudec et al. 2013, AAPG Bulletin |
| Size range of brine lakes in the Gulf of Mexico | from 1 m across to 20 km long | NOAA Ocean Explorer, Lakes Within Oceans, 2002 (archived) |
What the film simplifies
- The film says up to three times saltier. The measured top layer was 80 to 110 on the salinity scale, against about 35 for average seawater, so roughly 2 to 3 times. Press reports of 4 to 5 times saltier have no measurement behind them for this pool.
- The pool that talks, winks and sells itself like a spa is cartoon. So are the crab tourist in a towel, the rubber duck, the neon sign, the wine glass and the dinosaur licking salt.
- The jar of pickled crabs is a joke. Pickling means preserving in brine, and the explorers did see dead crabs preserved along the edge, but nobody bottled them.
- "Low oxygen" was not reported for this pool. It rests on studies of deep brine pools elsewhere, which have almost no oxygen.
- "Bottomless" is the pool's sales pitch. The sampling line stopped at about 19 m without touching a hard bottom, which is not the same as having no bottom.
- The glowing pool and the name suggest a hot tub. The brine measured about 8 °C (46 °F) and the mud under it about 19 °C (66 °F), far cooler than a real hot tub.
At a glance
Runtime 1 minute 2 seconds · Topics: Brine pools, Ocean chemistry, Deep sea life, Geology · Captions on YouTube · Full script below
Test yourself
Why doesn't the brine mix with the seawater above it?
Answer
It is much saltier, so it is heavier than seawater. It sinks and settles on the sea floor like a lake, with its own surface.
The top of the brine measured 80 to 110 on the salinity scale. Average seawater is about 35. About how many times saltier is the brine?
Answer
About 2 to 3 times. 80 divided by 35 is about 2.3, and 110 divided by 35 is about 3.1.
Where did the salt in the pool come from?
Answer
From a shallow sea that dried up here in the Middle Jurassic, more than 160 million years ago. Its salt was buried under the sea floor, and water seeping through it brings brine back up.
The script
The Jacuzzi: Come on in! The water's to die for.
Host: Stop! That's a lake... at the bottom of the ocean!
Host: Deep in the Gulf of Mexico. Scientists call it the Jacuzzi of Despair.
The Jacuzzi: Despair is such a strong word.
Crab: A lake? Does it have a beach?
Host: Kind of! Its water is up to three times saltier than the sea, so heavy it barely mixes.
Host: It pools up like a lake, and even spills over the side like a waterfall!
Host: The salt is from a sea that dried up here, about 160 million years ago.
The Jacuzzi: Vintage.
Crab: Sign me up!
The Jacuzzi: Bubbles!
Host: Methane.
The Jacuzzi: Bottomless!
Host: Really. A probe went down 19 meters and never found a solid bottom.
The Jacuzzi: Low oxygen... I mean, low stress!
Host: See the edge? Those are dead crabs, preserved by the brine.
Host: Basically... pickled.
The Jacuzzi: They loved it so much, they never left!
Crab: I'm good, thanks!
The Jacuzzi: Just a toe?
Sources
- The Jacuzzi of Despair: its nickname, the 3 m rim and the brine waterfall, 80 to 110 psu salinity, 7.8 °C brine over 19 °C mud, the 3 m brine layer, methane saturation and bubbles at two spots, the 19 m sampling line with no hard bottom, and dead crabs and isopods preserved along the edge.Cordes et al. 2016, Oceanography 29(1) supplement
- The pool lies nearly 3,300 ft down in the Gulf of Mexico, is 100 ft around, holds brine too dense to mix easily with seawater, and can be fatal to many animals that fall in.Ocean Exploration Trust, 2015
- Brine lakes have a distinct surface and shoreline; the Gulf was a shallow sea that dried out in the Middle Jurassic; Gulf brine lakes range from 1 m across to 20 km long.NOAA Ocean Explorer, Lakes Within Oceans, 2002 (archived)
- The submarine Johnson Sea Link floated on the surface of another Gulf of Mexico brine pool.NOAA Ocean Explorer, Johnson Sea Link photo caption, 2002 (archived)
- Average seawater salinity is about 35 parts per thousand.NOAA Ocean Service, Why Is the Ocean Salty?
- Deep brine pools have almost no oxygen; in the Red Sea pools an eel dipped into the brine, presumably for animals stunned or killed by it.Purkis et al. 2022, Communications Earth & Environment
- The Gulf of Mexico salt was laid down in the Callovian stage, more than 160 million years ago.Hudec et al. 2013, AAPG Bulletin