The possibility that changes in the ocean's Redfield ratios, in the ocean's plant productivity, or in the extent to which organic material is recycled within the ocean have significantly altered the atmosphere's CO2 content over the past century is examined. Models show that the magnitudes of the alterations in these processes necessary to produce significant CO2 changes are unreasonably large. For those who do not wish to accept this theoretical approach, we offer a means to directly monitor the impacts of life cycle changes. It involves determining temporal trends in the dissolved O2, NO3, and PO4 contents of thermocline waters. While surveys carried out in 1972 (GEOSECS) and in 1981 (Transient Tracers in the Ocean) reveal no significant trend for the thermocline of the North Atlantic over this 9-year period, a longer period of observations will be necessary before film limits can be placed through this observational approach.