Hi George, marine phytoplankton primary production is approximately 50 Pg-C per year. The unit Pg-C is “peta-grams of carbon.” 1 PgC=1×10^15 grams. That is, 15 zeros. To give you some context, the global primary production is about 100 PgC per year. This means that land plants and ocean phytoplankton carry out CO2 absorption by photosynthesis about equally.

Photosynthesis is season-dependent. On both land and in the ocean, photosynthesis occurs more in the spring and summer than in the fall and winter. Globally though, the seasons are flipped by hemispheres, so that the growing season in, for example, northern hemisphere, occurs at the same time as the non-growing season in the southern hemisphere.

How much CO2 does plankton photosynthasize each year? Is it season dependent?