About a day’s sailing from New Orleans, roughly a thousand metres down on the floor of the Gulf of Mexico, there is a pool of brine dense enough to sit on the seabed as a lake with its own surface and its own shoreline. The crew aboard the exploration vessel Nautilus called it the Jacuzzi of Despair, and the nickname has travelled a great deal further than the material behind it.

That material is thinner than most of the coverage suggests, and more interesting.

What the 2015 survey actually recorded

The pool was examined in May 2015 across two cruise legs of the Nautilus field season, using the remotely operated vehicle Hercules, during work on the cold seep and brine features of the deep Gulf. In its own account of the dive, the Ocean Exploration Trust gives the dimensions without decoration: a circular pool about 30 metres (100 feet) in circumference and roughly 3.7 metres (12 feet) deep, found nearly 3,300 feet below the surface, at 19 degrees Celsius, with what the Trust describes as high salt content. That temperature is what earned the jacuzzi comparison, since the water around it at that depth is far colder.

The often-repeated figure of four times the salinity of seawater comes from the same page, where it describes what brine at seep sites of this kind can reach. A measured salinity for this particular pool does not appear in any of the accounts we have read.

The write-up appeared not as a standalone peer-reviewed paper but as a short entry in the Oceanography 29(1) supplement, the annual field-season booklet edited that year by Katherine Bell, Michael Brennan, Joanne Flanders, Nicole Raineault and Katie Wagner. Supplements of that kind report preliminary results. Much of the 2016 press coverage described it as findings published in the journal Oceanography, which is true in the narrow sense and misleading in the useful one.

Depth figures in the coverage also fail to agree: the Trust says nearly 3,300 feet, while several outlets, including the Christian Science Monitor, reported 4,200 feet. We would use the expedition page, which is the operator’s own.

The salt is Jurassic

None of this is exotic chemistry, and the mechanism behind it is old, slow and well documented.

During the middle Jurassic, the Gulf was a shallow sea that lost its connection to the world ocean and dried out, leaving a salt layer described by Bob Carney of Louisiana State University, writing for NOAA’s Ocean Explorer programme, as up to eight kilometres thick. Rifting broke that layer into two sheets, the Louann in the north and the Campeche off western Yucatán. Sediment buried them, then loaded them, then deformed them. Where the salt now meets seawater it dissolves, and the resulting brine flows out across the seafloor in puddles, pools and channels that in some cases run for tens of kilometres.

So the Gulf floor is not dotted with anomalies. It is a salt province doing what salt provinces do, and the Jacuzzi of Despair is one legible instance of it.

The rim is the interesting part

The lethal reading is accurate as far as it goes. Crabs, amphipods and the occasional fish that stray in do not come out, and the brine that kills them also preserves them, which is why the images show intact bodies.

What the same footage shows, and what tends to get cropped out of the retelling, is that the margins are populated. Mussel beds and tube worm fields live at the rim, per the Trust’s account, sustained by chemosynthesis: bacterial symbionts converting methane and hydrogen sulphide from the seep into usable energy.

Rim ecology of this kind has been documented for decades. In 1990, Ian MacDonald and colleagues reported in Science a 540 square metre mussel bed ringing a brine-filled pockmark at 650 metres depth on the Louisiana slope, with brine measured at 121.35 practical salinity units and dissolved oxygen at or below 0.17 millilitres per litre. Twenty-five years of subsequent work on Gulf seeps sits between that paper and the 2015 dive. The pool visited by Hercules was new to that survey. Brine pools as a class were not new to anyone.

Why brine pools keep turning up in ocean-world conversations

Erik Cordes, an associate professor of biology at Temple University who worked on the site, put the appeal plainly in 2016. Speaking to Seeker, in remarks the Monitor relayed, he noted that many people study extreme habitats on Earth as models for what might be found elsewhere, and expected deep-sea technology development to be applied to those worlds.

The analogy is a research convention rather than a result, and papers on these sites routinely open with it. A hypersaline, anoxic, methane-charged pool on the Gulf seabed is somewhere to test instruments, sampling methods and assumptions about what tolerances life can hold, which argues for better tools rather than for conclusions about Europa, Enceladus or Martian brines.

What a lethal pool is good for

The most useful property of these features may have nothing to do with what dies in them.

Because the brine is anoxic, burrowing animals cannot occupy the sediment beneath it, so layers stay in the order they were laid down. Sam Purkis and colleagues at the University of Miami used that in a 2022 paper in Communications Earth and Environment, coring the NEOM brine pools in the Gulf of Aqaba and recovering a stratigraphy spanning at least 1,200 years. Turbidite beds appeared roughly every 25 years, attributed to flash floods and to the seismicity of the pull-apart basin the pools sit in. Coarse terrestrial material turned up about once a century, read as tsunami deposits.

The Gulf of Mexico has been running that experiment for longer, in a different pool. Orca Basin, about 350 kilometres southwest of New Orleans, holds a brine pool covering some 123 square kilometres and reaching 220 metres deep, at roughly eight times seawater salinity, fed by a Jurassic salt diapir outcropping on the basin’s eastern flank. Its anoxic bottom and near-absent bioturbation have made it a reference site for palaeoceanographic work on the last deglaciation of the Laurentide ice sheet.

Preservation there has proved less clean than the logic promises. Deep Sea Drilling Project Leg 96 recovered 92.5 metres of continuous core at Site 618 inside the pool, expecting a clean upper Neogene sequence, and hit a 16-metre landslide deposit at the seafloor. In a 2019 paper in Scientific Reports, Derek Sawyer, Alan Mason, Ann Cook and Alexey Portnov argue that landslides striking the Orca pool can raise waves in the brine with amplitudes on the order of hundreds of metres, enough to disturb the stratification these records depend on, and enough in principle to spill brine into the basin next door.

That puts the small pool back in proportion. It is a well-imaged instance of a common Gulf feature, surveyed once and written up in two pages of a field-season booklet. The Ocean Exploration Trust listed its own open questions after the 2015 dive: how these pools form, how they change over time, and how the organisms at the rim survive. Eleven years on, the middle question is the one to watch, and whether anyone has been back with a second high-resolution map is the first thing we would want to know.