Into The Oceanic Abyss - an idea

I've been watching a lot of David Atenborough documentaries lately, particularly the Blue Planet series, and I think the deep sea is an area for adventure that's not been covered much, particularly in the OSR. I'm tempted to write something up for it once the library module's done, so here's my thoughts.

Adventuring underwater is weird enough that I'd probably knock together a simple little system that goes in the front of the book for it, and notes for how to adapt it for other OSR stuff. Features would include a blend of LotFP and ItO, and then:

• Access to the deep sea is granted by 'pressurized diving suits' that are worn like armour. Each comes with air tanks that limit how long you can spend down there. The type of diving suit you wear is a function of your class (like armour is in normal games) and sets your AC, carrying capacity, manoeuvrability, and amount of air (which limits the time you can spend without surfacing).
• Air is a resource. You have X turns of air before you need to surface or start drowning. Exertion might use up turns of air.
• Injuries have a chance to damage your suit, resulting in loss of air, or even drowning. Maybe as a result of critical hits, or as part of an injury table when you hit 0 HP, or a chance on every hit.
• Weapons and other gear set up for underwater adventuring.
• Drowning and breath-holding will get more detail.
• XP for treasure, but you get paid by land-bound scientists for mapping and doccumenting the weird shit at the bottom of the sea (on commission, of course), and this pay counts as treasure for XP purposes. So you get XP just for exploring and recording what you find.

The setup is likely to be a hexcrawl, roughly dividing the map into a few biomes (chosen because I like them). You sail your little boat out to an area and plunge down to the ocean floor to explore. The biomes are probably going to be:
Coral reefs - close to the surface, lots of life and light, tight areas and 'rooted' animals (sea anemones etc) that act a lot like traps.
Coastal areas - close to the surface, lots of life and light, dangerous tides and currents.
The abyssal plain - deep down (getting that deep takes a turn of air, as does returning), no light, a vast wasteland. Spooky.
Geothermal areas -  deep down again, volcanic stuff, vents, and other weird hazards.
Abyssal chasms - giant canyons with Nasty Shit at the bottom. Rocky, dangerous, super deep super dark.

Each biome has an encounter table (of course) of different types of wildlife. Each plunge into a biome also roles on a 'location' table that gives you some specifics for where you are. Start exploring down there, and you roll up new 'locations' as you travel across the seabed.

There'll be a little port you can return to where you can recruit new PCs or NPC crew for your boat, trade your maps/drawings for money, buy gear, etc etc. But stuff above the surface is basically downtime.
Some hexes - a lot of them, probably - will have some unique features on them. These are little adventure sites, such as:
Underwater caves.
Whale carcasses- crawl into their innards and explore them like a mini-dungeon, maybe they swallowed cool shit worth looting. Maybe carcasses of other sea-monsters too.
Shipwrecks. A pretty straightforward minidungeon and an excuse for skeleton pirates. Super spooky haunted wrecks in the lightless abyss.
Cyclopean ruins constructed in the distant past by Aboleths. Lovecraftian nastiness and SUPER COOL loot. Possibility of Deep Ones. I should ask Kelvin green about having them be the same deep ones as in Fish Fuckers.

No central conceit really, just an excuse to run around in the deep ocean because seriously that shit is COOL AS FUCK and full of weird shit. Like the deep ocean is literally full of boggle-eyed tentacle monsters that eat each other constantly and glow in the dark, and there are giant smoking volcanic vents and leviathan carcasses that form year-long banquets where even the bones get devoured and that shit is RIPE for adventure.
Also there's a fuck ton of good public domain art of the deep sea, so that's a plus 'cos I do love using old public domain art. Like even if I wasn't writing stuff I'd have huge collections of illustrations from, like, the 1880s to 1930s, there's so much good stuff.
Also I have been bingeing nature documentaries and not slept in twenty hours, I am made of caffeine and inspiration.