Their existence isn't intuitive. You'd expect diffusion to dilute the pools and yet they seem to last a very long time somewhere on the order of thousands of years. It's not immediately obvious to me how the physics of these pools functions because there is a persistent interface as if the brine is another liquid entirely. From another paper, "Discovery of the deep-sea NEOM Brine Pools in the Gulf of Aqaba, Red Sea,"
The CTD measurements from 1200 m depth, through the brine pool interface (1769.46 m) and 2 m below (1771.50 m) revealed that the bathyal water column above the brine pool has a stable 21.33 °C temperature, the salinity of 40 PSU, and dissolved oxygen of 180 μmol L−1.
but if you sample the pool itself,
Within 15 cm beneath the brine interface, salinity rose from 40 PSU to values higher than the limits of the conductivity probe (120 PSU). Subsequent lab analysis of the brine provided actual salinity values of 160 PSU. Dissolved oxygen values fell more than 75% at the interface, reaching 50 μmol L−1 by 20 cm submergence into the brine, and further falling to a minimum value of <10 μmol L−1 by 50 cm below the interface.
The brine is also hotter than the water just above it,
Unlike salinity and dissolved oxygen, the temperature did not abruptly change across the brine interface. Instead, the temperature gradually increases below the brine interface at a rate of 0.1 °C per 20 cm depth increase, reaching an increment of 1.0 °C above the temperature of ambient seawater by 2 m depth into the brine (Fig. 4). The temperature differential to ambient did not increase with deeper submergence. Such a modest warming increment suggests the lack of proximal hydrothermal heating of the brine.
> You'd expect diffusion to dilute the pools and yet they seem to last a very long time somewhere on the order of thousands of years.
What I've learned from things like this is that my intuition for when diffusion should work, and how fast, is just busted.
The biggest example in my mind is pyroclastic flows from a volcano. For years (mostly as a kid), I didn't understand what they were because I kept thinking roughly "if it was just gas it couldn't hold together into a coherent flow, right?" Well, as far as I can tell, yeah, they're basically just gas, but really hot and full of rocks. I still don't really get why they hold together instead of poofing out into clouds, except that it has something to do with how they're denser than the surrounding atmosphere. They're sometimes also referred to as "pyroclastic density currents", go figure. https://en.wikipedia.org/wiki/Pyroclastic_flow
Another big one that threw me for a loop as a kid was "warm/cold air masses" interacting in a way that kept their identity. "why does the warm air mass ride up on top of the cool air instead of just mixing?" I guess the answer here is that they're just too big for the mixing to happen faster than the bulk motion.
Anyway, it seems like fluids, especially fluids of very different properties, especially different density, take their time mixing, sometimes long enough to let them act like separate objects in contact for much longer than I, for one, would think. Thousands of years in the case of these brine pools (though in this case, they're being at least partially refreshed). I wish I understood it better.
There's actually an even more common example that what you've described: water heaters. The cold inlet at the bottom and the hot outlet at the top prevent mixing, and the two waters of different temperatures can maintain their difference for a surprisingly long time.
« pyroclastic flows … basically just gas, but really hot and full of rocks »
Rocks fall to the ground (too heavy), but the eruptive cloud is still full of matter heavier/denser than air (e.g. CO2, volcanic dust and gas, forming crystal needles and “stone flakes” when cooling), and all this is thrown up miles high by thermics into a towering mushroom cloud, which eventually collapses, gaining speed on the vertical, and then flowing horizontally on hitting the relief. At least that's my understanding, assembling bits and pieces from documentaries over the years (Pompeii etc), but I have never seriously “studied” it.
These clouds (on the rise) and flows (on the way down) hold together because of density and gravity, and also because the volcano thermics have locality, perhaps not unlike a huge man-made fire (like in Hamburg or Dresden) creates its own local weather, resulting in a firestorm.
« why does the warm air mass ride up on top of the cool air instead of just mixing? » — Well, because it is lighter. Whereas a cold front moves like a wedge into warm air, throwing it up while staying close to the ground (cold = heavy), and thereby sometimes provoking frontal thunderstorms.
zeumo 1 hours ago [-]
An example that comes to mind is layered cocktails: the syrup layer will not diffuse into the upper layer (and vice versa) on a surprisingly long timescale (at least overnight)
There is a saying: you can't step into the same river twice. And I wonder if these pools aren't the same. Like there is constant mixing, but some other force maintains the conditions of the pool. Those particular water molecules and sodium ions haven't been there for a thousand years but were gradually replaced. That's my guess, anyway.
nephihaha 14 hours ago [-]
Extremely interesting page, thank you, am reading through it.
It's amazing what can live where. There are microbes a mile down and a mile up, in near boiling water and in subzero conditions.
14 hours ago [-]
ihsw 11 hours ago [-]
[dead]
ironqcold 13 hours ago [-]
That was interesting
13 hours ago [-]
Rendered at 09:48:13 GMT+0000 (UTC) with Wasmer Edge.
From the exploration vehicle Nautilus, https://www.youtube.com/watch?v=nGLtMWx28hs
Their existence isn't intuitive. You'd expect diffusion to dilute the pools and yet they seem to last a very long time somewhere on the order of thousands of years. It's not immediately obvious to me how the physics of these pools functions because there is a persistent interface as if the brine is another liquid entirely. From another paper, "Discovery of the deep-sea NEOM Brine Pools in the Gulf of Aqaba, Red Sea,"
but if you sample the pool itself, The brine is also hotter than the water just above it, from, https://www.nature.com/articles/s43247-022-00482-xNature is beautiful.
What I've learned from things like this is that my intuition for when diffusion should work, and how fast, is just busted.
The biggest example in my mind is pyroclastic flows from a volcano. For years (mostly as a kid), I didn't understand what they were because I kept thinking roughly "if it was just gas it couldn't hold together into a coherent flow, right?" Well, as far as I can tell, yeah, they're basically just gas, but really hot and full of rocks. I still don't really get why they hold together instead of poofing out into clouds, except that it has something to do with how they're denser than the surrounding atmosphere. They're sometimes also referred to as "pyroclastic density currents", go figure. https://en.wikipedia.org/wiki/Pyroclastic_flow
Another big one that threw me for a loop as a kid was "warm/cold air masses" interacting in a way that kept their identity. "why does the warm air mass ride up on top of the cool air instead of just mixing?" I guess the answer here is that they're just too big for the mixing to happen faster than the bulk motion.
Anyway, it seems like fluids, especially fluids of very different properties, especially different density, take their time mixing, sometimes long enough to let them act like separate objects in contact for much longer than I, for one, would think. Thousands of years in the case of these brine pools (though in this case, they're being at least partially refreshed). I wish I understood it better.
PS: I was half expecting this EV Nautilus brine pool video. Grim comedy of a sort. https://youtu.be/9ZYJAmAmFPw
https://www.youtube.com/watch?v=Bm7L-2J52GU
(technology connections describing it)
Rocks fall to the ground (too heavy), but the eruptive cloud is still full of matter heavier/denser than air (e.g. CO2, volcanic dust and gas, forming crystal needles and “stone flakes” when cooling), and all this is thrown up miles high by thermics into a towering mushroom cloud, which eventually collapses, gaining speed on the vertical, and then flowing horizontally on hitting the relief. At least that's my understanding, assembling bits and pieces from documentaries over the years (Pompeii etc), but I have never seriously “studied” it.
These clouds (on the rise) and flows (on the way down) hold together because of density and gravity, and also because the volcano thermics have locality, perhaps not unlike a huge man-made fire (like in Hamburg or Dresden) creates its own local weather, resulting in a firestorm.
« why does the warm air mass ride up on top of the cool air instead of just mixing? » — Well, because it is lighter. Whereas a cold front moves like a wedge into warm air, throwing it up while staying close to the ground (cold = heavy), and thereby sometimes provoking frontal thunderstorms.
It's amazing what can live where. There are microbes a mile down and a mile up, in near boiling water and in subzero conditions.