[analog31]

I'm thinking mainly about the Haber-Bosch process, which runs on methane, and feeds more than half of the world's animal population.

As mentioned in a sibling comment, it could run on some other heat source, but that hasn't been demonstrated yet on the scale of agriculture.

[ben_w]

Indeed, that's one of the main possibilities I guessed you were thinking of; for triggering algal blooms, one of the things suggested was iron. (And given it was immediately going into salt water, ore would presumably have been fine… if the hypothesis was correct).