According to wikipedia, during the azolla event, the azolla would grow in a fresh water layer at the top of the arctic ocean and then sink when it died. There

According to wikipedia, during the azolla event, the azolla would grow in a fresh water layer at the top of the arctic ocean and then sink when it died. There was a layer of oxygen-free water at the bottom, preventing it from decomposing. https://en.wikipedia.org/wiki/Azolla_event https://en.wikipedia.org/wiki/Azolla_event Ideally if we had a large fresh-water lake with a layer of anoxic water at the bottom, we could use it as a carbon-sequestering azolla farm with hardly any human input. All the examples given in wikipedia are salt water, though. Apparently decomposition itself removes oxygen from the water, so I suppose you could use any sufficiently deep body of water as long as it has very little in the way of mixing currents. https://en.wikipedia.org/wiki/Anoxic_waters https://en.wikipedia.org/wiki/Anoxic_waters I imagine that trying to have, say, lake Superior designated as an official azolla farm and deliberately rendered anoxic probably wouldn't be popular, even if it's possible. I wonder if it's possible to make a salt-water tolerant variant of azolla or duckweed? (I actually have some practical experience with azolla and duckweed, thanks to a pond I made during the pandemic. One or the other of those usually takes over in the spring and early summer, and then dies off in late summer, presumably because the water lettuce and water hyacinth out-compete them for nutrients. Azolla can survive the winter but duckweed does not. They both make good chicken food, but azolla seems to have more bulk to it.)