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Here are the terrestrial flow processes once again, but this time with the estimated magnitudes of flows included. Most of these are very large flows, and they have a seasonality to them — photosynthesis is obviously big in the growing season, but it is small in the winter. If land masses and land plants were equally divided in the northern and southern hemispheres, this seasonality would cancel out, but in today's world, a large majority of land and plants are in the northern hemisphere, so around July, photosynthesis is very strong. In fact, this on and off aspect of photosynthesis is the primary reason for the seasonal changes in atmospheric CO2 concentrations seen in the Mauna Loa record.

Schematic illustration to show terrestrial process of carbon flow
Carbon Flow in Terrestrial Reservoirs showing Fluxes
Credit: David Bice

Check Your Understanding

Terrestrial carbon cycle question:

What is a simple formula for photosynthesis?

A. O2 + Cellulose = H2O + CO2
B. CO2 + O2 +H2 = H2O +CO3
C. Sun + Light = CO2 + Cellulose
D. CO2 + H2O = Sugar + O2


Click for answer.

ANSWER:
D. CO2 + H2O = Sugar + O2. Photosynthesis uses CO2 from the atmosphere and produces O2.