Why build underwater outposts, rather than ocean-surface settlements?
Suppose we've colonized a planet with 99% of the surface area covered by oceans. It has submerged continental crusts, averaging 200-500m underwater, with the average depth of open ocean being 1000-1500m. Other than the difference in surface geography, consider the planet generally earthlike (unless deviating from Earth-normal conditions is necessary to answer the question).
Colonization was via slower-than-light generation ship, so this colony must be self-sufficient. Natural resources are mined from the rock of the continental shelf, which requires either above-water mining rigs or seafloor bases at shallowest parts of the ocean.
In the real world, surface ships and installations are far, far easier to build and sustain than their underwater equivalents. They don't need to be sealed against intense pressure and they're less mechanically complex to maintain, even if I posit a non-breathable atmosphere to eliminate the advantage of not needing to be sealed at all. But I'm looking for a reason or reasons to justify this colonial civilization being primarily aquatic, living in submarines and undersea installations exclusively, rather than ships and oversized oil rigs.
The best justification I've been able to come up with is extreme weather on the surface. According to this question/answer, a mere 133m depth is sufficient to ride out the worst storms overhead. However, since oil rigs seem able to survive hurricanes as long as they're built tall enough to avoid the worst of the waves, I'm skeptical that all the headache of an underwater city would be more attractive than just building a more storm-resistant above-water installation.
Simply put: Why live underwater, rather than on the surface of the ocean?
This post was sourced from https://worldbuilding.stackexchange.com/q/121226. It is licensed under CC BY-SA 4.0.
1 answer
Size, space, the room to breathe, and the necessity of dirt. They don't just want to be underwater (for protection from storms and radiation), they actually want to be in million-strong cities on land, they want space. On the ocean floor they can burrow to create underground caverns miles across and a mile deep, so they can have industrial zones, residential zones, business zones, government zones, various recreation zones, and farming and ranch zones, just like we do on Earth. With advanced scifi tech, this can all be fusion powered (fusion being performed in its own safe power generation zone), and lit up like daylight. With enough power, you could have a cold zone in there, for skiing or other snow sports.
The only thing you really need access to the actual sky for is astronomy and security for look out or receiving remote signals; that could all be done on ships, in person or remotely piloted. The ships and submarines can dock at the port to the underground city; which can be more like the size of one of our stadiums; not ten times the size of New York City like the actual underground city.
Underground their robot farms and ranches grow straight up Earth food, cucumbers and lettuce, apples and oranges and bananas. Chickens and eggs, butter and milk, if they haven't gone vegan. They've got robotic bees with photo-electric wings to gather power, for pollinations.
Even if they don't burrow in; it would be easier and more efficient and safer to maintain a thousand closely spaced domes underwater on the ground than to try and do the same thing with floating ships, subject to storms and waves.
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