An introduction to productivity and carbon cycling in aquatic ecosystems

Chapter 1. Productivity on planet Earth is largely dependent on the energy produced by hydrogen-fusion reactions in the Sun. Life is a key part of the carbon cycle. The abiotic input of CO2 degassing from volcanoes and metamorphism is only about one-thousandth of the biogenic exchange fluxes of CO2 through contemporary net primary production. Thus, one can view today's biosphere as a phenomenal carbon recycling system. Low rates of diffusion, the generation of low CO2 concentrations at times of high photoautotroph biomass and the kinetic properties of the primary carboxylation enzyme can limit aquatic productivity if this was based solely on inward passive diffusion of CO2 “pulled” in by carbon fixation. In aquatic environments, in contrast, especially in the oceans, most organisms possess a CCM to counter the low rates of CO2 diffusion in water and CO2 depletion when rapid CO2 uptake exceeds resupply.