They don't just gobble it up. Dead plankton, fish poop, and other organic material fall to the ocean floor and become another layer of sediment. Carbon is continually being removed from the atmosphere by biological processes. Those seams of coal we mine were, long ago, vegetation which got buried.
Yup.
Trying to keep this pithy. Could add lots of other facts but then it might become overlong. That said, might incorporate parts of what you said into the next time I post this info. Thanks!