Why is shallow water more dense than deep water? Shouldn’t it be the opposite?

I think that shallow water is subjected to evaporation almost in its totality and tends to get denser almost uniformly as water evaporates and the concentration of carbonates/salts increases....

Deep water can mix letting the denser superficial portion (from evaporation) to sink and mix with the less dense below...

But mind you, this is only my guess….

Interesting question. I thought water was totally incompressible (or perhaps I forgot anything I may have briefly learned about compressibility). Click on this link for a discussion on Wikipedia: https://tutor.hix.ai

This Wikipedia webpage convinces me that water is compressed slightly under pressure. Scroll down to the Contents table and click the section on Compressibility. But what I see there does not suggest that the density decreases as pressure increases. I have to ask why you have the feeling that shallow water is more dense than deep water.

For density to decrease as pressure increases, volume would have to increase. Notice that it says

I believe that means that as pressure increases, the compressibility and volume decreases.

Any time it is compressed the least bit under higher pressures, that would mean that the density increases. If compressibility decreased to zero at some point as pressure increased, that would mean that volume no longer changed in response to the increasing pressure.

I hope this helps, Steve

Shallow water can be denser than deep water due to temperature and salinity variations. When water is shallow, it is more exposed to external factors such as sunlight and atmospheric conditions. As a result, shallow water can experience higher rates of evaporation, which increases the concentration of dissolved salts and minerals, leading to greater density. Additionally, shallow water bodies may also have more organic matter and sedimentation, further contributing to density.

Furthermore, in certain situations, temperature differences can play a significant role. For example, during periods of stratification, where warmer water sits atop cooler water, the warmer surface water may become denser due to higher levels of dissolved salts or other factors, resulting in a denser layer at the top.

Overall, while deep water can have greater pressure from the weight of the water column above it, which can compress it and increase its density, shallow water bodies are subject to various other factors that can outweigh this effect and lead to higher density.