The ocean (Option A) is the largest carbon reservoir, storing about 39,000 gigatons of carbon—far more than forests or the atmosphere. It absorbs:

About 30% of human CO₂ emissions annually, buffering climate change.

Carbon through the biological pump, where plankton absorb CO₂.

Option B (Rainforests) are crucial carbon sinks, but they store significantly less carbon than oceans.

Option C (Atmosphere) holds about 750 gigatons of carbon, much less than the ocean reservoir.