If you stretch out the timescale horizontally it is close to sinusoidal.
There does seem to be a slight sawtooth effect. A smoother rise followed by a more rapid fall.
But if you think about what vegetation is doing, that fits. Plants slowly gather resources and build structures for reproduction. This extra mass and activity absorbs CO2.
When the plants have successfully reproduced (spread fruit and seeds) the most efficient strategy is to quickly discard the reproductive support structure and processes that are no longer required. So the CO2 intake falls rapidly.
Autumn leaves falling are one of many symptoms of this, though decaying vegetation also releases CO2
There does seem to be a slight sawtooth effect. A smoother rise followed by a more rapid fall.
But if you think about what vegetation is doing, that fits. Plants slowly gather resources and build structures for reproduction. This extra mass and activity absorbs CO2.
When the plants have successfully reproduced (spread fruit and seeds) the most efficient strategy is to quickly discard the reproductive support structure and processes that are no longer required. So the CO2 intake falls rapidly.
Autumn leaves falling are one of many symptoms of this, though decaying vegetation also releases CO2