Pore water chemistry sensitivity

Because diagenesis may alter only a small fraction of the solid phases, its impact may be difficult to detect from studies of solid phases alone. Pore water chemistry is much more sensitive to such changes. For example, in a sediment of 80% porosity, dissolution... 

The application of lanthanides as indicators of paleoredox conditions must take into consideration their diagenetic chemistry (German and Elderfield 1990). More sensitive analytical methods are required before the lanthanide pore water chemistry of deep ocean sediments can be studied. This research subject is challenging and would provide answers to the transport rate of lanthanides across the sediment/water interface in pelagic enviromnents. 

Most of our understanding of the marine chemistry of trace metals rests on research done since 1970. Prior to this, the accuracy of concentration measurements was limited by lack of instrumental sensitivity and contamination problems. The latter is a consequence of the ubiquitous presence of metal in the hulls of research vessels, paint, hydrowires, sampling bottles, and laboratories. To surmount these problems, ultra-clean sampling and analysis techniques have been developed. New methods such as anodic stripping voltammetry are providing a means by which concentration measurements can be made directly in seawater and pore waters. Most other methods require the laborious isolation of the trace metals from the sample prior to analysis to eliminate interferences caused by the highly concentrated major ions. 

The buildup of pore-water constituents in the bioturbated zone is extremely sensitive to the number and, to a lesser extent, size of burrows present. This demonstrates that at any given time sediment chemistry may vary in accordance with the abundance, individual size, and relative mobilities of the animals present. The often-observed decrease in population abundance during winter, for example, may in part be responsible for the reduction in biological influence on pore-water profiles at that time. The spatial variation in pore-water profiles in the Sound are shown to be consistent with the bathymetric variation in the animal communities present. 

As the precipitation of carbonates from the pore water is very sensitive to variables like porosity, permeability, texture and composition of the fill mass, the water depth, temperature and chemistry of the pore water and the burial depth, the resulting cementation may be highly variable as well, both in terms of strength and in terms of spatial distribution (vertical and lateral extent). 

The difficulty in direct synthesis of mesoporous transition metal oxides by soft templating (surfactant micelles) arises from their air- and moisture-sensitive sol-gel chemistry [4,10,11]. On the other hand, mesoporous silica materials can be synthesized in nimierous different solvent systems (i.e., water or water-alcohol mixtures), various synthetic conditions (Le., acidic or basic, various concentration and temperature ranges), and in the presence of organic (Le., TMB) and inorganic additives (e.g., CT, SO, and NOs ) [12-15]. The flexibility in synthesis conditions allows one to synthesize mesoporous silica materials with tunable pore sizes (2-50 nm), mesostructures (Le., 2D Hexagonal, FCC, and BCC), bimodal porosity, and morphologies (Le., spheres, rods, ropes, and cubes) [12,14,16-19]. Such a control on the physicochemical parameters of mesoporous TM oxides is desired for enhanced catalytic, electronic, magnetic, and optical properties. Therefore, use... 

---