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Dead Pools

Short answer: Brine pools are lakes on the seafloor: pockets of brine so dense they don't mix with the seawater above, complete with shorelines and even waterfalls.

They form where seawater dissolves salt deposits buried under the seabed, such as the layers left when the ancient Gulf of Mexico evaporated, or the evaporites of the Red Sea rift. The best-known example, the Gulf of Mexico's 'Jacuzzi of Despair', lies about 1,000 m down and is about 30 m around. Its brine runs 80 to 110 psu (normal seawater is about 35). It's warm, nearly oxygen-free and charged with methane and hydrogen sulfide. Crabs, isopods and fish that wander in die, and their bodies are preserved along its rim.

VideoWrite-up5 sources

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What should you know about Dead Pools?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. The Gulf of Mexico's 'Jacuzzi of Despair' is a lake on the seafloor, about 1,000 m down, four to five times saltier than the ocean around it.

    DD-049-F01 · Write-up · Exhibit C (How salty)

  2. Animals that stray into seafloor brine pools die from the salt, low oxygen and toxic gases, and their bodies are preserved along the rim.

    DD-049-F02 · Write-up · Exhibit B (Where the salt comes from)

Video transcript: Dead Pools: There Are Lakes at the Bottom of the Sea

DID YOU KNOW? Underwater brine pools are extremely salty, dense bodies of water that form on the seafloor when salt-rich fluids seep out of the Earth's crust and settle into depressions, creating sharp, visible boundaries surrounding seawater. Because the salinity is several times higher than normal ocean water, these pools are toxic to most marine life, causing fish and other animals that fall in to become stunned or die. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 21.7s Reel ·

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Dead Pools: There Are Lakes at the Bottom of the Sea Instagram Reel · · 21.7s

The write-up

There are lakes at the bottom of the sea. Some are four to five times saltier than seawater, with little or no oxygen.

  1. Exhibit A

    Lakes under the sea

    Brine is so much denser than seawater that it pools on the seabed with its own shoreline. The Jacuzzi of Despair is a crater-like pool that rises 3 m above the seafloor and spills brine over one edge in a 'waterfall'.

  2. Exhibit B

    Where the salt comes from

    Millions of years ago the Gulf of Mexico was shallower, and evaporation left thick salt layers that were later buried. As those layers shift and crack, seawater dissolves the salt, and the brine collects on the seafloor along routes also used by rising oil and gas.

  3. Exhibit C

    How salty

    The top 3 m of the Jacuzzi of Despair measured 80 to 110 psu, about four to five times saltier than the surrounding ocean (about 35 psu). Beneath it was hydrocarbon-charged fluid mud at 19 °C.

  4. Exhibit D

    What makes them deadly

    It isn't only the salt. The brine has little or no oxygen and is rich in methane and hydrogen sulfide.

  5. Exhibit E

    Pickled remains

    Researchers found dead isopods and crabs preserved along the pool's edge. In the words of Woods Hole scientist Scott Wankel, creatures that fall in 'die and get pickled and preserved.'

  6. Exhibit F

    Bottomless

    A sensor lowered about 19 m into the pool never reached a hard bottom, and methane bubbles were seen rising from inside.

Questions people ask about Dead Pools

Why doesn't brine mix with the seawater above it?

It sits on the seabed with its own shoreline.

Source: Write-up · Exhibit A (Lakes under the sea) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

About how much saltier is the 'Jacuzzi of Despair' than the surrounding ocean?

It measured 80 to 110 psu vs about 35 for seawater.

Source: Write-up · Exhibit C (How salty) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

Where does the Gulf of Mexico's brine salt come from?

Seawater dissolves the salt as the layers crack.

Source: Write-up · Exhibit B (Where the salt comes from) · The Jacuzzi of Despair Is a Deadly Lake Within the Gulf of Mexico (Discovery); Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

Besides salt, what makes brine pools deadly?

Animals that fall in suffocate in a toxic chemical soup.

Source: Write-up · Exhibit D (What makes them deadly) · 'Jacuzzi of Despair' Found in Gulf of Mexico (VOA News, 2016); The Jacuzzi of Despair Is a Deadly Lake Within the Gulf of Mexico (Discovery)

What did scientists find along the Jacuzzi of Despair's edge?

The brine 'pickles' animals that fall in.

Source: Write-up · Exhibit E (Pickled remains) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); 'Jacuzzi of Despair' Found in Gulf of Mexico (VOA News, 2016)

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Why doesn't brine mix with the seawater above it?

    1. It's colder
    2. It's much denser
    3. It's magnetic
    4. It's frozen
    Show the answer

    Answer: B. It's much denser It sits on the seabed with its own shoreline. Source: Write-up · Exhibit A (Lakes under the sea) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

  2. About how much saltier is the 'Jacuzzi of Despair' than the surrounding ocean?

    1. The same
    2. About 10% saltier
    3. Four to five times
    4. 100 times
    Show the answer

    Answer: C. Four to five times It measured 80 to 110 psu vs about 35 for seawater. Source: Write-up · Exhibit C (How salty) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

  3. Where does the Gulf of Mexico's brine salt come from?

    1. Rivers
    2. Buried salt layers left by an evaporated ancient sea
    3. Ships
    4. Volcanoes
    Show the answer

    Answer: B. Buried salt layers left by an evaporated ancient sea Seawater dissolves the salt as the layers crack. Source: Write-up · Exhibit B (Where the salt comes from) · The Jacuzzi of Despair Is a Deadly Lake Within the Gulf of Mexico (Discovery); Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); How this 'Jacuzzi of Despair' formed beneath the Gulf of Mexico (Christian Science Monitor, 2016)

  4. Besides salt, what makes brine pools deadly?

    1. Radiation
    2. Little oxygen plus methane and hydrogen sulfide
    3. Electricity
    4. Sharp rocks
    Show the answer

    Answer: B. Little oxygen plus methane and hydrogen sulfide Animals that fall in suffocate in a toxic chemical soup. Source: Write-up · Exhibit D (What makes them deadly) · 'Jacuzzi of Despair' Found in Gulf of Mexico (VOA News, 2016); The Jacuzzi of Despair Is a Deadly Lake Within the Gulf of Mexico (Discovery)

  5. What did scientists find along the Jacuzzi of Despair's edge?

    1. Gold
    2. Preserved dead crabs and isopods
    3. Shipwrecks
    4. Ice
    Show the answer

    Answer: B. Preserved dead crabs and isopods The brine 'pickles' animals that fall in. Source: Write-up · Exhibit E (Pickled remains) · Wankel et al., ROV Hercules Investigates Brine Lakes on the Bottom of the Ocean (Oceanography, 2016); 'Jacuzzi of Despair' Found in Gulf of Mexico (VOA News, 2016)

Cite this case file

Easterling, Marcus. "Dead Pools." The Detail Department (DetailEnjoyer), case file DD-049, last updated Jan 19, 2026. https://detailenjoyer.com/case/dead-pools/

Permalink: https://detailenjoyer.com/case/dead-pools/ · Last updated

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