Underwater physics and dynamics

[Vvashjr]

Hello all, in the story that I am writing, I'm having some of my main characters visit an underwater kingdom, specifically a mer kingdom, as one of them is actually half mer. Im curious and slightly challenged how to handle to presence of sunlight down on the ocean floor.

Obviously it cannot be too deep until it's abyssal dark. But neither can it sit on somewhere so shallow that beachgoers can easily access it. How would you recommend I "place" it, and the issue with light?

What about water pressure? I read a few novels that has underwater cities(Forgotten Realm's Queen of the Depths, Dragonlance's The Alien Sea etc) and they seem to disregard that either. I would like to know if you do so too to minimise too much complications and doubts

Also have anyone dealt with sea(water) species, especially half human/mammalian. Did anyone of you touch on how the humanoid part of the body deals with immersion in water or usually writers skim over that? Im also trying to decide should I touch on that aspect, because if I do bring up that topic, I also have to deal with my land-dwellers' skin and hair being submerged for at least a week in sea-water(they are visiting the undersea kingdom).

Would appreciate your thoughts on these. Feel free to raise any possible issues from an underwater realm for me too.

 

[Russ]

What a great question.

I don't actually have any answers for you, as I know squat about underwater physics etc. But if I was interested in building a moderately realistic underwater city and have people visit it, I would be concerned about the bends etc.

I would think you could get lots of good info on this kind of stuff at some scuba diving sites.

How much "sciency" stuff you put in your fantasy is a very personal choice, so you have lots of room to work here with your own style. You can do everything from ignoring it, magically handwaving it away, all the way to using hard science to figure it all out.

Any which way you go it sounds like a fun project.

 

[Svrtnsse]

I wouldn't worry too much about the light and the water pressure.

If the underwater city is deep enough that sunlight wouldn't reach it you can just handle it in the same way you would an underground city, or a city shrouded in perpetual night. You'd add some kind of local light source, like luminescent shrimp or something. The pressure would be an issue if you were to actually account for it, but you can magic it away in some fashion - perhaps have the visitors consume something that strengthens their bodies or lowers the pressure around them.

As for placement: the seas have shallow areas even far from land. There are underwater mountain ranges, and while some of them reach above the surface to create islands, there's no reason they can't reach only to just below the surface.

When it comes to half-breeds I would just skim over the effect of the water on the land-dwelling part of the body and hair. I find it pretty easy to accept that the humanoid part of a merperson has adapted to constant submersion. When it comes to land-dwellers it's more of an interesting question. You can add a little depth (no pun intended) to the story by showing how they handle the constant contact with water.

Another thing that may be worth considering is underwater movement for land dwellers. You move much slower under water than on land, and activities like fighting or fleeing will be very different.

 

[Vvashjr]

What a great question.

I don't actually have any answers for you, as I know squat about underwater physics etc. But if I was interested in building a moderately realistic underwater city and have people visit it, I would be concerned about the bends etc.

I would think you could get lots of good info on this kind of stuff at some scuba diving sites.

How much "sciency" stuff you put in your fantasy is a very personal choice, so you have lots of room to work here with your own style. You can do everything from ignoring it, magically handwaving it away, all the way to using hard science to figure it all out.

Any which way you go it sounds like a fun project.

Oh right I forgot about the bends. Hmmm...

I'll try to browse some diving sites and

I wouldn't worry too much about the light and the water pressure.

If the underwater city is deep enough that sunlight wouldn't reach it you can just handle it in the same way you would an underground city, or a city shrouded in perpetual night. You'd add some kind of local light source, like luminescent shrimp or something. The pressure would be an issue if you were to actually account for it, but you can magic it away in some fashion - perhaps have the visitors consume something that strengthens their bodies or lowers the pressure around them.

As for placement: the seas have shallow areas even far from land. There are underwater mountain ranges, and while some of them reach above the surface to create islands, there's no reason they can't reach only to just below the surface.

When it comes to half-breeds I would just skim over the effect of the water on the land-dwelling part of the body and hair. I find it pretty easy to accept that the humanoid part of a merperson has adapted to constant submersion. When it comes to land-dwellers it's more of an interesting question. You can add a little depth (no pun intended) to the story by showing how they handle the constant contact with water.

Another thing that may be worth considering is underwater movement for land dwellers. You move much slower under water than on land, and activities like fighting or fleeing will be very different.

Thanks for the advise on shallow seas that are far out. I nvr thought of tht before.

 

[Svrtnsse]

One more thing to consider - refraction. When light moves from one medium (like air) to another (like water) it changes direction based on the angle it enters at. If everything in the city is underwater this isn't an issue, but if there are areas that are filled with air (like for example sleeping quarters for visiting land-dwellers) it might potentially be an issue.

 

[psychotick]

Hi,

Light and water depth is a strange mix.First the sunlight generally only penetrates the ocean in any appreciable amount to a depth of two hundred metres. Beyond this it's pretty much black. But on the way down the colours change as the water filters out the different light spectra. So early on it's the reds that vanish, but as you go deeper the colours keep getting progressively filtered out until at two hundred metres you're fairly much left with blue. Of course if you have torches suddenly you have white light again. But at a distance the light from the torch will slowly appear to become blue.

The other thing to remember is refraction as was mentioned before. One interesting thing about this is that if you're underwater looking up, from certain angles the ocean surface starts to look like a mirror.

Bends are an issue, but most sea life has certain physiological adaptations that make this less of an issue for them. For example whales have very high haemoglobin levels in their blood to store oxygen and can collapse their lungs at depths (sounds worse than it is - it just means that they can essentially squeeze the alveoli of their lungs so that the air in their lungs doesn't reach them - which in turn means that the eighty percent of it that's nitrogen doesn't cause them problems).

Cheers, Greg.

 

[Vvashjr]

Thank you so much guys. Lots of invaluable information.

So I shld just ignore pressure to make things easy?

 

[psychotick]

Hi,

No, I wouldn't. Most life in the oceans finds certain levels / depths where it is most suited to live. Go deeper and the pressure increases and some critters won't like it. Go shallower and other critters won't like it. Think of it as sort of like different terrain. Some people are better adapted to deserts, some to beaches, some to forests. So maybe your merfolk are the same. Some like it deeper - maybe they have physical adaptations that separate them from others of their people. Some like it shallower - and again they look a little different. Suddenly you have different races / sub-races of merfolk. And they might differ in other ways too - such as their level of tolerance for surface dwellers!

Cheers, Greg.

 

[Vvashjr]

Hi,

No, I wouldn't. Most life in the oceans finds certain levels / depths where it is most suited to live. Go deeper and the pressure increases and some critters won't like it. Go shallower and other critters won't like it. Think of it as sort of like different terrain. Some people are better adapted to deserts, some to beaches, some to forests. So maybe your merfolk are the same. Some like it deeper - maybe they have physical adaptations that separate them from others of their people. Some like it shallower - and again they look a little different. Suddenly you have different races / sub-races of merfolk. And they might differ in other ways too - such as their level of tolerance for surface dwellers!

Cheers, Greg.

Ahhhh makes sense! Thanks! Didnt think of the sub-races yet as I keep thinking of sea races as homogeneous like whole races of mer, sea elves, sea goblins etc. Didnt occur to me to sub-race them.

 

[Chekaman]

Merskin will be different to cope with water and the cold as well.