waters, where methane-oxidizing bacteria convert part of it to carbon 

 dioxide. In the Red Sea, hydrocarbon gases (methane through the 

 butanes) are brought up by hot springs in contact with organic sediment 

 at depth. Major rivers carry dissolved methane from the continents 

 to the oceans. The movement of hydrocarbon gases has been traced 

 in a few specific areas, but httle is known of fluxes in and out of the 

 oceans. 



Transport of dissolved hydrocarbon gases from more deeply buried, 

 compacting sediments to permeable, near-surface beds is particularly 

 important. A phenomenon of these accumulations is the formation 

 of gas hydrates (solids resembling ice), with the approximate formula 

 CH4(H20)6. Methane hydrates form from 0° to 24°C and at pressures of 

 400 to 6000 psi (equivalent to a total water-sediment column of about 300 

 to 4667 meters). They are believed to be widespread in sediments of 

 continental margins, where bottom temperatures and pressures are 

 conducive to their formation. They can cause sub-bottom reflections 

 because of the high velocity of seismic waves in the crystalline hydrate 

 layers, which can reach thicknesses of 500 meters. We need to know 

 more about the origin, occurrence, and distribution of these gas hydrate 

 layers in sub-bottom sediments. Core barrels need to be built that can 

 take and retain samples at their subsurface pressures. Such equipment 

 is available from the oil industry, but it needs modification for research 

 programs. 



REDOX POTENTIAL, pH AND ALKALINITY 



For some elements the formation and concentration of chemical 

 species depend on biological processes that directly or indirectly alter 

 the redox potential, the pH, and the alkalinity. These processes can be 

 nonbiological, biological, or some combination of both. 



Redox Potential 



The oceans are in a dynamic state with respect to oxidation and 

 reduction. There are significant differences in the redox environment 

 of the surface in contact with oxygen in the atmosphere, the deep waters 

 that bathe the sediments. In between are intermediate zones resulting 

 from diff"usion and advection, or the lack of them, and from varying 

 biological activities. Most redox reactions in the oceans depend on the 

 activities of the biota. Redox levels within microenvironments close to 

 biological surfaces may diff"er from those in the macroenvironment. 

 Marine organisms internally mediate redox reactions by acting as 

 centers of variant oxidation potential (e.g., the photosynthesizing cell 

 is a center of low pE, permitting the reduction of CO2 to glucose). 



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