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his_rotundity_ t1_is1rcg3 wrote

Cooled water from the poles sinks as a result of both its salinity and temperature profile. Cooler water is denser than warmer water. Cooler water with high amounts of salt is even more dense. So it sinks and is replaced by less dense and less saline (fresher) water. So yes, the salinity of water increases with depth. See this.

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GammaFork t1_is4j6lc wrote

Though oddly the densest, deepest class of global water, Antarctic Bottom Water, is actually fresher than the overlying Circumpolar Deep Water or North Atlantic Deep Water!

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CroStormShadow t1_is76unb wrote

What makes that possible?

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brunswick t1_isaflbs wrote

The density of seawater is affected by both temperature and salinity. The exact relationship is pretty complicated, but fresher water can be denser than more saline water if it's considerably colder. That's why physical oceanography has a concept of spiciness. Warm and salty water is 'spicy' while cold and fresher water is 'minty.' Because density is affected by both salinity and temperature, minty and spicy water can potentially have exactly the same density.

Here are a couple of figures I pulled from Talley's Descriptive Physical Oceanography textbook. Here's a map showing the temperature and the salinity of the circumpolar deep water around Antarctica. If you compare it to the Antarctic bottom water, you can see that the Antarctic bottom water is a little fresher than the CDW, but it's considerably colder.

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Gorstag t1_is4kzj5 wrote

Intuitively I would think the opposite would be true. For example sweet tea is heated to add more sugar. Your explanation allowed me to logically see why the phenomenon occurs with salt in the ocean. Kudos.

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Fun_Wind7710 t1_is55xj6 wrote

Different compounds have different temperatures where they have peak solubility in water. Oxygen is more soluble in cold water, for example.

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TrueBeluga t1_is5h47b wrote

That’s because oxygen is a gas. Gases are more soluble in cold water, solids more soluble in hot water.

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kawaiisatanu t1_is5cd22 wrote

No, the real answer is that salt (sea salt is mostly just NaCl) has a solubility way higher than the amount of salt in the sea, so of course you can have saltier colder water than less salty warm water.

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UtsuhoMori t1_is5dyd4 wrote

iirc it's more about the state of matter of the molecules being dissolved; As in oxygen is more soluble in cold water because it's a gas at room temp and salt is more soluble in hot water because it's a solid at room temp.

Excess heat energy in a liquid allows gas to escape easier, reducing solubility of gas in hot water. On the other hand, excess heat energy is needed in order to free more molecules from a solid like sodium chloride and keep them in solution.

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atomfullerene t1_is7rlm6 wrote

Heating things does let you dissolve more into it, but the ocean isn't near the maximum amount of salt that could be dissolved in it.

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