Rainforests, and the Sargasso Sea, continue to have very impressive amounts of plant biomass, despite the best efforts of all animals combined to eat them. It'

Rainforests, and the Sargasso Sea, continue to have very impressive amounts of plant biomass, despite the best efforts of all animals combined to eat them. It's easy to imagine a current which sunk a Sargasso's worth of algae every year removing carbon. There's not enough oxygen on the bottom to support metabolizing that much sugar.