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I'm designing a scuba-diving expedition in the Permian sea Panthalassa. Pre-dive planning for the optimal gas mix and critical pressures requires factoring in gas available but also readings on the environment. In terms of composition, it appears that Permian seawater is virtually identical to that of the modern ocean, according to this study. However, the Permian ocean temperature was notably higher than the modern ocean (80°F+/26.7°C+ versus 60.9°F/16.1°C). This would predispose divers to overheating more, perhaps, but this isn't that special when examining regional differences in today's oceans.

It sounds so well and good, but the similarities actually undermine things. I want special boutiques of diving companies to offer diving solutions specifically for swimming in the Permian seas.

  • I had imagined their value-add to be mostly in the form of cost-savings: maximize dive time given volume of gas.
  • Their knowledge of the world was supposed to afford them an edge over normal scuba companies who just use conventional gas mixes and critical pressures.

Clearly, the issue is that if conditions are more or less the same, then anyone with diving expertise would be able to design pre-dive plans for the Permian seas. To them, the Permian would just be a new location where all the old rules apply. I definitely don't want that for my world.

Question

Granted there will be regional/location differences (just as there are in today's oceans), but based on empirical findings, is there universally unique about the Permian seas that would prompt adjustments of 'present-day' calculations of gas mixes and critical-pressures?

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is there [anything] universally unique about the Permian seas that would prompt adjustments of 'present-day' calculations of gas mixes and critical-pressures?

Nope. Gas mixtures are primarily driven by water pressure after all, and water pressure isn't going to be noticeably different.

What is different though is the composition of the atmosphere. "Permian" is a bit of a broad time period (nearly 50 million years) but it included times when atmospheric O2 was very high (~30%) and times when it was very low (~15%), and also periods of lower atmospheric CO2. This is going to have very important knock-on effects on post-dive offgassing, treatment of various kinds of diving accident, and operation of compressors to refill gas bottles locally. Clearly, dive operations will benefit from some surface operations expertise and equipment.

I suspect (but I'm definitely not certain) that this will have a greater effect on free-diving, especially the circumstances under which the swimmer will black out mid-dive. This would seem to increase the hazard for more experienced people. I don't believe that regular diving would be affected to nearly the same extent, however.

To them, the Permian would just be a new location where all the old rules apply. I definitely don't want that for my world.

Then you'll need to find a substantially more alien ocean in which to swim. The Permian sea just ain't different enough, and even the atmosphere isn't going to be that different for very broad swathes of time within the period.

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Add value by knowing the ecosystem

Before the days of the dinosaurs, there was a time when the ancestors of mammals ruled. Permian sharks had reason to fear the Dimetrodon and Tappenosaurus, among others. Not that the sharks should be taken lightly - I would hate to be the fellow in the shark cage when Helicoprion comes calling, with a coiled toothy plumbing snake ready to scrape the tasty meat out of that hard shell.

Then there is the question of venom. Even in our time it is very hard to predict when you're going to pick up a worm-like amphibian or cute cuddly primate only to find out it has a nasty surprise. Someone could have studied old fossils all their life and still not expect the poisonous spine that ends the expedition. You want to have trustworthy dive guides to help keep you out of trouble.

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