Abyss

* See also Persephone
* See also Geothermal_Power
* See also Sea Slugs
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Rapture Built Over a Glowey Biomass ... :
I forget if there is any mention (in the game) of a link between this 'glowing biomass' and the Sea Slugs miraculous ADAM venom. These Sea Slugs ( which are mollusks ) are too big and have the wrong body parts to be 'filter feeding' of any glowey' stuff floating in the water -- Assuming that imparts any of this ADAM-type properties.
A whole ecosystem of larger seabed living organisms thus is required instead of some stuff floating in the water. ( The Sea Slugs eat things that themselves absorb the 'glowey' weirdness ). 
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Oblivion as a name for a place near the Abyss ( when actually off the Volcano/Sea Mount Rapture is built upon, the seabed plunges to an average over 3000 feet deep ).
A bar overlooking "the Abyss" ( If its glowey in the water, then you really can't see much, and any detail fades away in about 200 feet anyway. ) Gimmick probably there is 'glass floors'.
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Plunging Into The Abyss - New Ride At BioShock-land :
How much of Persephone was lost when Sofia Lamb blew up some supports in her sour-grapes bid at extortion/suicide. It was first the Inner Persephone (North Cell Blocks), and then likely was only part of that set of buildings ( various sections were joined by those narrow easily broken connecting tubes ). The few explosions we heard were not enough to cut the supports on such a large massive building complex ( much of which is embedded in the cavern cliff faces ). I guess we will have to go back there to see what is left. Possibly the demolition was all a deception - yet another attempt to manipulate ( That 'last' pile of explosives wasn't even on a structural support of Persephone -- Sofia was herself a few dozen feet away, and would have been killed by a large explosion. Tip - fermented urine (amonium nitrate) mixed with fuel oil don't much make an effective explosive ).
Eleanor says the building will plunge miles deep (assuming ...), but if she has had the Big Sister changes, then she could probably survive it ( and depending on the Alpha conversions, so could Delta ).
I actually wonder why they (Rapturians) went to the effort to make the (BS2) Persephone Prison so fancy. You can't really see much of it from inside, and it is in a cavern, so is not visible from anywhere else in the City. Make it 'foreboding' looking ?? When it is mostly just the inmates who ever see it AFTER committing their criminal acts ?? Suspending it over the edge of the Abyss had to make it more expensive to construct - hardly anything you would think Sinclair would bother to pay extra for, so it had to have been built that way previous to his appointment as Rapture's jail-keeper. Originally a research center for the Abyss and a possible Tourist Attraction ?? Possibly. It would help explain those other oddities.
Basically : Pretty Game Scenery ...
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"The Abyss Elevator" 
Big Daddies ( and some purpose-built Submarines ) can withstand the pressure down to the much greater depths in the Abyss (4000+ foot) -- What is down there that you would want to go there for ( Hopefully NOT an Alien Spacecraft - not in this genre ) ???
* The Elevator descends down to various levels of the Abyss
* Bioluminescent Sea_Life organisms - Alot of research would be done on these in Rapture, eventually resulting in many low-power 'BioLume' lights.
* Sea Slug harvesting ( even the wrong types are used for research and some new technologies )
* An unique ecological zone ( the Abyss is shielded by the volcano sides and warmed by the nearby geothermal activity ). Some odd ancient lifeforms were starting to be found.
* Became a tourist 'adventure' with a 'fail-safe' elevator capsule ( which only failed once on that last trip ... )
* Rapture standard diver hard suits are limited to 1000 ft depth ( used within the City environs ), and special ( more expensive ) 'Deep Suits' allow to 6000 ft ( which Big Daddies can also withstand ).
* Fortunate that 'The Abyss' didn't turn into Rapture's "garbage dump" ( probably simply because it was far enough away to be inconvenient. )
* Still many mysteries are to be explored 'down there'.
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Rapture Built Over a Glowey Biomass ...
I forget if there is any mention (in the game) of a link between this 'glowing biomass' and the Sea Slugs miraculous venom. These Sea Slugs ( which are Mollusks ) are too large, and have the wrong body parts to be 'filter feeding' any glowey' stuff floating in the water ( assuming that imparts any of this ADAM type properties ).
A whole ecosystem of larger seabed living organisms thus is required instead of some stuff floating in the water.
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Magic Underwater Places (Abyss) :
Bioluminescence exists quite alot in nature, but its faint is light visible more than 20 feet away (basic physics/optics). The light diffuses in water so fast that a 'big' mass (glow) can't be seen from even rather close distances.
An organism Making itself glow wastes alot of energy, which is problematic in small/single celled organisms. Maybe the writers were thinking of the types of glowing algae seen flashing in some tropical waters ( of course that is a Sun-powered metabolism at the Ocean's surface with its plentiful resources ).
Assuming that there are any nutrients to support a 'big' mass of anything down there. I hope they didn't expect/think it to be 'nuclear radiation' to cause magical 'Mutations', cuz radiation kills off things really really well in most cases.
There are some (REAL) places they've found in the deep ocean, at volcanic vents on the seabed, with localized sulfur chemical leakage and warmth, which allow anaerobic bacteria to grow and thus a food chain. They have a quite close cluster of organisms eating that bacteria and each other. It all happens in the SMALL vent's immediate vicinity in a few places. If the vent is too big ( and a big volume of superheated water ), then the heat scalds to death everything nearby. Too far away ( the heat diffusing ) it is back to the ambient cold temperature and sterile low oxygen environment. There is a whole ocean full of near-ice-cold water to keep some large 'pocket' of warmth from stably forming. Caverns, with trapped water ? It is back to 'scalding'.
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Tourism Potential ...
I could see Sinclair having a tourist center in Persephone ( It is actually absurd that that HUGE place could possibly have been a "Secret" ).
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H P Lovecrafthttps://conservapedia.com/H._P._Lovecraft did not need Faux-Science for his storytelling. Seriously, the Fantasy type of things they had in Infinite BS's plot/story/interview-explanations was being REJECTED by Pulp Magazines back in the 1950's.
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