In yet another entry in the "it is! It isn't! It is! It isn't" saga of global warming, we have this New Scientist article:

Antarctic krill appear to feed at the surface of the ocean and “parachute” down to deep waters more often than previously thought, a new study reveals, suggesting they take a bigger bite out of the carbon that contributes to global warming.

They're small, but there are a lot of them, so the carbon they're... umm... "depositing" comes out to (according to the article) about the same amount that 35 million cars emit in a year. Busy little critters, I'll give them that.