374 



REINERS 



complicated by the fact that the carbonate which will undergo solution is generally 

 surrounded by a matrix of silicate detritus. If we are to make long-range predictions, 

 these kinetic questions must be studied. 



In summary, Broecker et al. 16 estimate that the sea will continue to remove 

 about 40% of excess carbon and that, within 200 years, marine acidity will reach 

 the point at which CaC0 3 sediments will begin to dissolve. At that time the sea 

 will be able to take up even larger amounts of C0 2 . Thus the ocean will 

 ultimately absorb enormous amounts of excess CO2 , but the kinetics are slow, 

 and, in the shorter run of the order of 100 years, the atmosphere will hold about 

 60% of excess C0 2 produced, and we must address ourselves to the climatic and 

 biological consequences of such a change. 



Clearly, there are many vital questions to be investigated in the marine 

 geochemistry of carbon. Perhaps the two broad areas requiring the most 

 attention are investigations of ocean mixing, particularly of carbon (compare 

 Stuiver, and Bacastow and Keeling, this volume), and elucidation of the kinetics 

 and controlling factors for dissolved C0 2 interaction with sediments (compare 

 Broecker, Cooke, this volume). In addition, considerable insight on the relation 

 of geotectonic plate movement to the lysoclinal boundary, and the long-term 

 stability of oceanic carbon dynamics can be gained by careful analysis of oxygen 

 and carbon isotope ratios in the sediments as explained by Broecker. 



Primary Production and Organic Sedimentation 



Eutrophication may be enhancing phytoplankton growth in certain areas. 

 The extent of increased primary production in coastal waters is not known. It is 

 important to know the amount of organic matter that is sedimented. This 

 question is discussed briefly in the papers by Stuiver, and Woodwell, Rich, and 

 Hall. 



The Biosphere 



Probably the largest single question involving the biosphere and the carbon 

 cycle concerns the extent to which the biota and detritus are acting as sinks for 

 excess atmospheric carbon. As shown in Fig. 1, 3.6 X 10 tons of carbon are 

 currently added to the atmosphere each year. Yet atmospheric content is 

 increasing by 0.7 to 1.5 ppM per year, or 1.8 to 3.6 X 10 9 tons. About half the 

 injected carbon is going into the oceans or the biota or both. Estimates on the 

 rate of carbon movement into the oceans based on l C gradients were presented 

 in several papers of the Brookhaven Symposium. These estimates indicated that 

 the biotic pool must be increasing in size (e.g., Bacastow and Keeling, this 

 volume). Whittaker and Likens, on the other hand, contend that biotic mass is 

 decreasing, not increasing, and that these decreases are due to man's activities, 

 principally through conversion of forest land to agriculture, decreases in 

 productivity, and general environmental toxification. Reiners supports the latter 



