APPENDIX 373 



itself would take up only about one-tenth of the increase. Thus transfer to the 

 deep sea is an important limiting process for distribution of excess carbon. 

 Broecker et al. 16 also calculated that the surface layer comes to relatively rapid 

 equilibration with the atmosphere, indicating that it is not an important 

 rate-limiting barrier to movement of atmospheric CO2 into deep water. The 

 expanding coverage of petroleum films on the ocean surface may become of 

 increasing significance in this respect. 



The Deep Layer 



Carbon from the shallow layer mixes with deep water through advection, 

 diffusion, and sinking remains of the biota. Deep-water outcrops and advective 

 processes make calculation of mixing an extremely complex process. The 

 technique of measuring 14 C/ 12 C isotopic ratios is especially complicated by 

 outcrop exposure to the atmosphere and the poor understanding that exists on 

 exchange in these outcrops. Broecker et al. 16 calculated that, as fossil fuels are 

 burned, the percentage distribution of excess carbon will remain the same as at 

 present in the order of 50 to 67% in the atmosphere, 5 to 7% in the warm ocean 

 layer, 23 to 28% in the thermocline, and to 20% in the deep ocean. 



Sedimentation 



As the acidity of the ocean rises from increased C0 2 solution, sedimented 

 CaC0 3 will begin to dissolve. The conversion of CaC0 3 to Ca 2+ and 2HC0 3 

 through acid solution effectively doubles the capacity for dissolved C0 2 . . f^ 

 Carbonate solubility appears to be a complex function of temperature, salinity,"^ " 

 and pressure and does not increase linearly with depth. Instead, there is a 

 distinct boundary, termed the "lysocline," above which carbonate precipitation 

 predominates and below which carbonate dissolution predominates. The depth 

 of this lysocline can rise or fall as a function of dissolved C0 2 and other factors 

 and thus act as a negative-feedback-control mechanism. According to Broecker 

 et al., 1 6 there is sufficient CaC0 3 in the upper centimeter of marine sediment to 

 neutralize all the excess C0 2 already produced by man. Therefore carbonate 

 sediments represent an enormous pool that can buffer C0 2 changes in the 

 atmosphere. 



The kinetics of this buffering capacity are poorly understood. Some of the 



uncertainties were discussed by Broecker et al. 



Considerably smaller amounts of C0 2 are needed to bring deeper waters to 

 undersaturation. However, considerably smaller amounts of C0 2 have been made 

 available at these depths. The question as to whether solution will commence first in 

 the deep sea or in the surface water thus involves a detailed knowledge as to how 

 C0 2 penetrates into the sea. As we are not currently in a position to do any more 

 than guess, this question is best left undiscussed. 



Another problem that arises is how fast the neutralization will proceed once 

 undersaturation is achieved at any given depth. Very little is known regarding the 

 rates of solution of calcium carbonate in seawater. The problem is further 



