Sulfate reduction has been extensively studied (Berner, 1964) in 

 recent sediments. It would be valuable to know the kinetics of particulate 

 and dissolved organic carbon oxidation to complement such studies. 

 Silicates are being modeled for equilibrium and kinetic considerations 

 (Wollast, 1967; Helgeson, 1971; Luce et al., 1972), but the actual 

 kinetics have been studied on few of these minerals. In every study 

 using concentration gradients in sediments for modeling, the physical 

 properties of sediments should be determined to allow at least first-order 

 tortuosity corrections for the diffusion term using porosity measurements 



Estuarine and shelf sediments are less completely studied than deep- 

 sea sediments. Because of the higher sedimentation rates, larger pH-Eh 

 fluctuations, more active bioperturbation of sediments and their higher 

 organic contents, their chemistries are more varied and invite additional 

 study. The sediment-water interface must also be studied more closely 

 to understand the transition from particulate suspended matter to actual 

 sediment. Concentration profiles in the water above the sediment have 

 only been measured by sampling devices that disturb the system sampled. 

 While such devices provide useful information for large-scale gradients 

 (e.g., 1 to 10 m), it may be possible to observe the actual interface gradi- 

 ents only by using in-situ devices over 1- to 3-month periods. Measure- 

 ments of the radon flux should be attempted to estimate mixing and 

 turbulence for the bottom waters. 



DETERMINATION OF THE EXCHANGE OF GASES 

 BETWEEN THE ATMOSPHERE AND THE SEA 



Much remains to be learned about regional and mesoscale air-sea 

 transport of gases. Predictive models related to man's modification of 

 the atmosphere and ocean depend vitally on information of this sort. 



Human activities have brought about changes in the balance of gases 

 dissolved in the oceans and present in the atmosphere (Bolin and Eriks- 

 son, 1959; Broecker et al., 1971; and Machta, 1972). These changes 

 range from the introduction of trace and bulk constituents, such as 

 by-products of civilization, to the possible alteration of natural processes 

 by agricultural and industrial activities (Goldberg, 1971). Since the 

 International Geophysical Year, continuous clean-air baseline measure- 

 ments of several atmospheric gases have led to the discovery of secular 

 increases in their content in the atmosphere. These increases have 

 been most evident in the case of carbon dioxide (Brown and Keeling, 

 1965; Pales and KeeHng, 1965) and more recently in tropospheric 

 ozone (Komhyr et al., 1971; and Kelley, 1972). 



For carbon dioxide, it is estimated that 30 to 40% of the input by man 

 to the atmosphere has entered the sea (Machta, 1972; Broecker et al., 



39 



