Methane Clathrate
en.wikipedia.orgI found this article while making my way about Wikipedia (as you do).
It's ice that burns: cages of water trapping methane, and indeed the largest non-atmospheric store of it on earth. It forms interesting fractals under a microscope, has subtle and historical climate effects, fosters methanotroph communities. It has commercial interest for methane extraction and may work well for static methane storage.
A fascinating topic to stumble upon!
Did you follow up to https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis ?
Not so subtle at all...