User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-24769282-20140810040047/@comment-75.36.142.53-20140810161631

Stuff brought from the surface would include things you (individuals, businesses, industries) need and just cant get from the ocean. A toolmaker would bring his own supply of special tool materials - a whole stockpile of them - knowing that replacement materials would likely be non-existant, inferior, or horribly expensive.

Organics are often the base materials of plastics and  materials like carbon used in numerous industrial processes can be charcoal - made from heat purified  organic matter.

As for soils, their nutrients commonly need to be replenished (as the plants absorb them and the endproduct goes out the cities sewers  (recycling potential there -- Sinclair no doubt)

Some materials like copper/rubber are used in large amounts in the modern world, and even on the surface the places producing copper/rubber are far between. SO again many materails will simply have to be massively stockpiled - sufficient replacement for Raptures lifetime (100 years?)

And some of the items made from those special materials you might as well have them built-up into the endproduct on the surface where it can be done cheaper (so hard-to-make spare parts might also be stockpiled). Remember alot of industrial processes used to produce  the materials (and parts) is quite specialized,  requiring skills that there just wouldnt be enough people in Rapture with for so many (its not JUST the material, but all the tools required for those processes). Scale of production also is a factor, economy of scale on the surface can be magnitudes more cost effective than a small scale shop/craftsman operation.