effect of the terrestrial vegetation to the amplitude increase in atmospheric CO, at Mauna Loa Observatory

An observed increase of the amplitude of the seasonal cycle of atmospheric COz at Mauna Loa Observatory has been examined. Previous global carbon cycle studies seemed to suggest, at least qualitatively, that the observed increase may be entirely due to a C 0 2 fertilization effect on the terrestrial biota. The present detailed theoretical investigation shows that a pure C 0 2 stimulation of the net primary production may indeed lead to an amplitude increase of 0.15 plus 0.17 % yr-1 and minus 0.10 % yr-l as compared to the measured value of 0.67 f 0.25 % yr-l for the period between ~ ~ J 9 5 8 and AD 1987. This result is based on the assumption of a long term fertilization factor B with a range between 0.15 and 0.60, taken to be equal to the mesaured short term fertilization factor 8, obtained in C 0 2 enrichment studies with exposure times generally smaller than 1 year. The experimental evaluation of the difference between the relative increase of the summer (peak to trough) and winter (trough to peak) amplitude gives information on the carbon sequestered annually by the terrestrial ecosystems. With the estimated respiration response factor, which characterizes the fraction of the additional production that is consumed _ by ecosystem respiration, equal to 0.75, and a