Pore fluid—sediment chemistries

Figure 4. Pore fluid/sediment chemistries and abundance of sulfate reducers from the various cores.

The main objective of this research effort was to characterize diagenetic transformations among the various sulfide phases and analyze pore fluid chemistry with respect to depth. In addition, it also examined if the overlying organic-rich Spartina marsh sediments affected the formation of iron sulfides in the underlying sediments. 

Even where it is not occluded, the mineral surface may not be reactive. In the va-dose zone, the surface may not be fully in contact with water or may contact water only intermittently. In the saturated zone, a mineral may touch virtually immobile water within isolated portions of the sediment s pore structure. Fluid chemistry in such microenvironments may bear little relationship to the bulk chemistry of the pore water. Since groundwater flow tends to be channeled through the most permeable portions of the subsurface, furthermore, fluids may bypass many or most of the mineral grains in a sediment or rock. The latter phenomenon is especially pronounced in fractured rocks, where only the mineral surfaces lining the fracture may be reactive. 

A significant amount of seawater is trapped in the open spaces that exist between the particles in marine sediments. This fluid is termed pore water or interstitial water. Marine sediments are the site of many chemical reactions, such as sulfate reduction, as well as mineral precipitation and dissolution. These sedimentary reactions can alter the major ion ratios. As a result, the chemical composition of pore water is usually quite different from that of seawater. The chemistry of marine sediments is the subject of Part 111. 

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