Role of the marine biosphere in the global carbon cycle

Abstract

The geochemical disequilibrium of our planet is due mainly to carbon sequestration by marine organisms over geological time. Changes in atmospheric CO2 during interglacial-glacial transitions require biological sequestration of carbon in the oceans. Nutrient-limited export flux from new production in surface waters is the key process in this sequestration. The most common model for export flux ignores potentially important nutrient sources and export mechanisms. Export flux occurs as a result of biological processes whose complexity appears not to be accommodated by the principal classes of simulation models, this being especially true for food webs dominated by single-celled protists whose trophic function is more dispersed than among the multicelled metazoa. The fashionable question concerning a hypothetical “missing sink” for CO2 emissions is unanswerable because of imprecision in our knowledge of critical flux rates. This question also diverts attention from more relevant studies of how the biological pump may be perturbed by climatic consequences of CO2 emissions. Under available scenarios for climate change, such responses may seem more likely to reinforce, rather than mitigate, the rate of increase of atmospheric CO2.