There are 5 carbon sinks that are actuatable on a short time scale:
- Atmosphere (smallest sink)
- Surface ocean layers
- Fossil Fuel Reserves (largest sink)
Carbonate rock and deep ocean are both long-term sinks that change on the order of 1000s of years.
However, recent advancements mean capturing CO2 in Carbonate rock has become a possibility. The CarbFix project capured and calcified 95% of the carbon emissions of a coal plant in Iceland. Of course, this process requires energy too, but it's one more tool in the swiss-army knife.