What should an inactive planet's topography be for nutrient circulation?

Question

I'm trying to engineer an Earth mass planet built initially out of pure silicon dioxide (silica). So basically, imagine a glass sphere slightly larger than Earth somewhere in the Goldilocks zone, preferably closer to the outer region. Keep in mind that this planet has no moon, so there is no tidal heating. The inside of my glass ball is cold (and I want to keep it that way). The tilt of the planet is something smaller than Earth's, around 15°. Then, out of the same silica I need to shape the relief (well get back here in a second). Afterwards, my engineers build an equatorial magnetic ring system, which is basically a conductive ring on tall stilts that circulates current around the equator, powered by solar panels (also highly elevated) that are in the immediate vicinity of the ring, on both sides. The width of this solar panel fields should be enough to power the ring in order to obtain a magnetic field a few times (maybe 20?) more powerful than Earth's (since we have no atmosphere at the start so we need to collect the solar wind at a high rate for hydrogen, oxygen and nitrogen).

So, up to this point we have a smooth glass ball with a planetary magnetic shield generator that can be powered on anytime. As you might have guessed, I'm trying to make the planet habitable, and as a matter of fact very comfortable (nice and mild temp. range, no extreme weather phenomena).

Issues/Questions:

1. Question was moved here: How to stabilize the tilt of a planet without heating its core from tidal forces
2. Since there is no plate tectonics and volcanism, there is no natural circulation for elements such as carbon, calcium and nitrogen. This is the most important part and the core of this post: How should I design the topography of the planet (altitudes in every point, from the lowest point of reference - since there is no water yet), so that when I add the water (some will be formed from the captured solar wind, but it will be a very long process, so I'll just transfer an ocean of unsalted water to my paradise in the making) there will be no "dead zones" in the ocean where the nutrients get deposited and there are no currents to move it in a coastal region or even just the surface so plankton gets access to them?

My ideas for the second question were that:

• I could add a "cone hat" continent on each pole, covering the entire polar circle (here between 75° and 90° latitude) that would facilitate the formation of ice. When it would "slide off the cone hat's edge" (polar cap meets the ocean of fresh water and does the iceberg thingy) the melting of the ice would create a current in the ocean. If it needs to be focused in order to have a direction, then I could make the said continents more horseshoe shaped, so that ice falls off and meets the water predominantly in a certain region.
• I could make the ocean shallow (what was again the maximum depth at which sunlight can reach? 200 meters?) and also flat (so there will be no deposition zones designated by topography)
• I could make the entire dryland areas to be at most Madagascar sized islands equally distributed on the surface and placed in such a way as to not create any calm areas in the water around them (such as deviating a current from the water area between island A and island B - then that area would become a deposition area, which is not wanted).
• I could add genetically engineered species that feed in the ocean but live, die, breed on land, or marine species that commit suicide on the shores so that nutrients would be continually moved from the ocean to the continents.
• I could design the continents/islands with an edge on their perimeter (just a few tens of meters tall, not Km) so that they act as food plates and not spill the nutrients into the ocean too readily

Notes:

• I do not want to create a textbook planet, I want to make an engineered resort planet kind of thing
• all the other elements needed for life (iron, sulfur, carbon, phosphorus, etc.) will be added in "perfect quantities as to generate biosphere" (meaning that I don't need a few billion tons of iron if the biosphere's weight is limited by another element [most likely phosphorous])
• I will add mountain ranges on the continents/islands keeping in mind the Hadley cells in order to avoid the generation of arid areas/deserts.
• the end salinity of the ocean would be something along the lines of 0.1%-0.25% - so it will actually be barely drinkable by humans
• once the atmosphere reaches 1-1.2 atm. of pressure, the magnetic shield can be toned down to something similar to Earth, so we avoid gaining any more atmospheric mass.
• I think this is a good thought experiment for when we try to terraform Mars (since the plate tectonics and volcanism are gone) as well as for when Earth will go through a similar state (long after the Sun explodes, but whatever).

Bonus question: what would you recommend as a chemical insulant between the planet body and the highly reactive chemistry of the biosphere/ocean/atmosphere? Is silicon dioxide inert enough to leave it unprotected, or I would need to add protection so the planet doesn't get corroded? (I'm afraid of the occasional spontaneous production of nitrous acid, which AFAIK melts/eats glass).

If every issue is resolved then we will end-up with an ultra stable, predictable, and unchanging planet designed with habitability in mind. Which will be preferable to the ever-changing ever-dying planet that we are on right now.

Bottom line: I want to change the paradigm of the concept of a planet from a chemical actor in the surface processes, into just the structural body on which those processes take place (so I want to un-involve/isolate the planet from the water-air-biosphere chemistry happening above, but still make those processes work, although maybe altered)

Answer 1

There are a few things you can do to ensure nutrient circulation on your planet. First, you can make sure that the continents are evenly distributed and not too large. This will prevent areas of the ocean from becoming stagnant. Second, you can add mountain ranges on the continents to help circulate nutrients. Third, you can add genetically engineered species that feed in the ocean but live, die, and breed on land. This will help to move nutrients from the ocean to the continents. Finally, you can design the continents with an edge on their perimeter so that they act as food plates and not spill the nutrients into the ocean too readily.

Answer 2

You have a few misunderstandings.

1. Solar wind doesn't deposit elements, it blows them away. That's why the inner planets aren't gas giants. Our magnetic field actually keeps our lighter elements from getting blown away. Without it, we might look more like Venus.

2. You don't need moons for tidal force. If the planet rotates, then the star will create tidal force, slowly turning rotational momentum into heat through deforming the shape of the sphere as it rotates.

3. Air is circulated due to uneven heating between the equator and the poles. Hot air at the equator rises and flows towards the poles, then drops down at around 30 degrees latitude. Planetary rotation then makes a chaotic mess of this.

Cool water surfaces don't create updrafts, so the warm tropical air comes down from the Hadley cells over large bodies of water in the 30-60 degree latitude range, which is what makes the west coast of North America warmer than it should be around Washington and Oregon, and warms the Mediterranean and Black seas. If you wanted to evenly distribute heat across the planet, then you'd want to put a ring of maybe six bodies of water across the 50 degree mark.

Not sure how that would translate into water currents, but you'd probably wind up with something that looked like a Faberge Egg.

On the magnetic field thing, the calculations that I've seen suggest that solar power wouldn't be enough to maintain a magnetic field. The back-of-napkin calculation suggests that photovoltaics would need somewhere around 110% of the Earth's surface to power your ring, assuming that the entire surface were laid flat, facing the sun. If your race can create planets, then they might also create a Dyson Swarm to power it, use fusion powered, or just inserting an iron core in the planet and spin it.

The latter would also solve some of your density problems. Glass has slightly less than half of the density of the Earth, so you'd need a much larger sphere to generate 1G.