Submareef

The vast majority of the open ocean is relatively barren. There are a few good reasons for humans to want to change this; solar powered sequestration of CO2, food production, the ability to provide new stable habitat for ocean organisms. All ideas involving adding nutrients from external sources fail because the ecosystem is entirely dependent on the external source of nutriment. I propose an effective, if somewhat complicated alternative. Submerged floating landmass. A massive buoyant structure submerged to the depth of a reef, in the light zone but deep enough for substantial upward growth. This structure would allow the formation of reef organisms which would filter out and retain much of the material that fell down from the ecosystem above, thus conserving the minerals. Since the majority of the elements needed to sustain life are available in ocean water, a submerged island would also serve to aggregate the more unavailable nutrients allowing for a life supporting surplus in the surrounding region. To adapt to the fact that the weight of the Submareef will increase as it establishes, I recommend that it be made in a mesh pattern that will gradually fill in and become solid. This mesh should have a bell shape that will eventually allow the underside surface to retain a substantial pocket of air which would need to be added by human means.

To maximize the viability of the concept I would recommend considering something in the scale of a quarter mile round. Once the reef reached a critical size it could be allowed to sink or towed into an area of shallow water. Reefs of this size could also be sunk atop one another to form atolls in areas of relatively shallow depth.