[lemming]

> Any studies on the effect of of both marine animals and the beach/dune/fringe dwellers on this?

https://www.projectvesta.org are doing those studies, they've been on HN before: https://news.ycombinator.com/item?id=20403570, that thread answers a lot of your questions. It's based on very sound-looking science, pioneered by Olaf Schuiling in the Netherlands (see here for more explanations: https://greensand.com/en/pages/werking-olivijn-steen).

> What's the ratio of carbon-stored to carbon-released here?

There's about a 4% loss, mostly due to crushing the olivine and shipping it around. https://projectvesta.org/science/#dflip-df_978/1/.

According to Schuiling's calculations, about 7 cubic kilometres of olivine a year would offset all of humanity's emissions. For reference, the largest mine in the world is the Bingham copper mine in Utah, which is (IIRC) about 23 cubic kilometres. So, it's a lot, but it's within the reach of current technology. Schuiling estimated it would take an industry roughly the size of today's oil industry to operate, probably around a million employees. Again, it's big, but it doesn't require any new magic air-sucking machines or anything like that, it's just what we already know how to do, on a scale that we already do it. And hopefully we'll have lots of coal miners out of work soon who would know how to do it.