52 EKDAHL AND KEELING 



natural gas) has accumulated in the atmosphere. The remainder has been taken 

 up by the two other major pools in the short-term global carbon cycle — the 

 oceans and the land biota (biosphere). Two long series of direct measurements of 

 the rise in atmospheric carbon dioxide will now be used to establish the fraction 

 of industrial C0 2 remaining airborne. Knowledge of this fraction and of spatial 

 and temporal variations in natural radiocarbon will then be used in an attempt to 

 estimate how much industrial C0 2 is taken up separately by the oceans and land 

 biota. 



A central problem in producing this estimate is to formulate a satisfactory 

 model of the carbon cycle. The problem is difficult because certain experimental 

 parameters cannot be determined accurately. The modeling problem will be 

 considered in two parts. In the first, presented in this paper, two determinative 

 attributes of the carbon cycle will be examined separately: (1) the ability of the 

 atmosphere, coupled with the ocean and land biota, to attenuate stratospheric 

 oscillations in natural radiocarbon and (2) the ability of the same reservoirs to 

 redistribute an exponentially growing source of inactive industrial CO2 injected 

 into the lower atmosphere. We seek to establish how predictions of attenuation 

 and redistribution are affected bv assumed transfer times, reservoir sizes, and 

 growth rates, when these parameters are varied over a wide range of values. By 

 using a mathematical technique involving a transfer function (equivalent to an 

 integral transform), we gain this information without solving completely the set 

 of governing differential equations of the model under investigation. 



In part II of this study, presented in the next paper, 1 the geochemical 

 models examined in this paper are used together with estimates of the annual 

 rates of production of radiocarbon and industrial C0 2 to make year-to-year 

 predictions. These predictions are then compared with direct observations as a 

 means of further testing of the models. Finally a narrow range of model 

 parameters is selected and used in predicting future changes in the short-term 

 global carbon cycle. 



DIRECT MEASUREMENTS OF ATMOSPHERIC C0 2 



Annual changes in atmospheric C0 2 concentration have been documented 

 by Bolin and Bischof using discrete-sample analysis of air collected on aircraft, 

 as well as by Kelley 3 and Keeling 4 ' 5 and their coworkers using continuous 

 recording ground-based gas analyzers supplemented by discrete samples. The two 

 longest and most continuous records will now be discussed in detail. Both 

 records are extensions of earlier published data and are expressed on the basis of 

 the same provisional absolute calibration. 6 ' 7 



A nearly uninterrupted series of atmospheric C0 2 measurements made with 

 a continuous C0 2 gas analyzer at the Mauna Loa high-altitude observatory on 

 the island of Hawaii now extends over a period of 14 years. This record was 

 gained by comparison of the concentration of atmospheric C0 2 up to 96 times 

 per day with reference gas mixtures calibrated at the Scripps Institution of 



