Anoxic bottom water

Shanks, W.C., III, Woodruff, L.G., Jilson, G.A., Jennings, D.S., Modene, J.S., Ryan, B.D. 1987. Sulfur and lead isotope studies of stratiform Zn-Pb-Ag deposits. Anvil Range, Yukon Basinal brine exhalation and anoxic bottom-water mixing. Economic Geology, 82, 600-634. 

It has been shown by mineralogical, chemical and X-ray-diffraction analyses that the major part of reduced sulfur occurs in the form of pyrite in ancient sediments (Lein, 1978)81). It has been also established that pyrite may form rapidly in muds of recent sediments. In anoxic bottom waters, pyrite formation can take place before and after burial even during sedimentation (Berner, 1984)89). Also the geological occurrence and chemical stability relations indicate that authigenic pyrites can be synsedimentary or diagenetic (Kalliokosky, 1966)90). 

Figure 11.4 Negative log correlation between concentrations of sulfide (pmol L 1) and of Fe2+ (pmol L 1) in anoxic bottom waters in marine and freshwater systems. (Modified from Gunnars et al., 2004.)...

Roden, E.E., and Tuttle, J.H. (1992) Sulfide release from estuarine sediments underlying anoxic bottom water. Limnol. Oceanogr. 37, 725-738. 

Hoeft, S.E., Lucas, F., Hollibaugh, J.T., Oremland, R.S. (2002). Characterization of microbial arsenate reduction in the anoxic bottom waters of Mono Lake, California. Geomicrobiol. J. 19 23-40. 

Similary, in freshwater and non-sulfidic brackish environments with strong O2 demand, dissolved ferrous-iron may accumulate in groundwaters and anoxic bottom waters. Significant iron oxidation will occur where the water... 

Sediment anaerobic processes anoxic bottom water 437... 

Research in anoxic environments has suggested that some minor and trace elements are precipitated where free dissolved sulfide is present without undergoing a valency change, whereas others undergo a change in valency and are either more efficiently adsorbed onto solid surfaces under oxic or anoxic conditions or are precipitated under anoxic conditions. Therefore, the enrichment of many trace elements relative to their crustal abundances indicates only that the sediments accumulated under anoxic conditions, although not necessarily under anoxic bottom waters. However, Calvert and Pedersen (1993) demonstrated that I and Mn enrichments are reliable indicators of bottom... 

A comparison of organic matter (OM) components in cores from Dabob Bay (oxic bottom waters) and Saanich Inlet (anoxic bottom waters) indicates that 02 availability ultimately has little or no independent effect on OM preservation in these environments (Cowie Hedges, 1992). Comparative analyses of organic compounds in sediment traps and bottom sediments from Saanich Inlet indicates that the anoxic benthic interface is an important site of diagenesis, and that selective removal takes place at both compound-class and molecular levels (Cowie etal., 1992). Preferential loss of marine organic material is indicated by the calculated delta-C-13 value and biochemical composition of the substrate. 

Saelen, G., Bottrell, S.H., Raiswell, R., Talbot, M.R. and Skei, J.M. (1993) Heavy sedimentary sulfur isotopes as indicators of super-anoxic bottom-water conditions. Geology, 21, 1091-1094. 

Would you expect a higher (than Redfield) ratio in marine sediments under oxic or anoxic bottom water conditions ... 

There are other such examples. Many unsaturated soils are known to convert to N2(g> via NO3 (i.e., nitrification then denitrification). They achieve this because there are local oxic and anoxic environments in the soil waters that, respectively, allow nitrification and denitrification to proceed. In stratified lakes, nitrification may occur in the oxygenated epilimnion (upper layer) and denitrification in the hypolimnion (bottom water) and in the sediment pore water where dissolved oxygen concentrations fall to zero. The nitrification and denitrification process is important in preserving the fishery in Indian Creek Reservoir in the Sierra Nevada mountains. This reservoir is fed by the tertiary effluent from the City of South Lake Tahoe sewage treatment plant. The effluent has at times contained 15 to 20 mg NH4 N/liter. Levels of ammonia of this magnitude are toxic to fish, yet in the reservoir there is a thriving fishery. This is achieved because the top waters of the lake nitrify the ammonia to nitrate and this is reduced to N2(g) by the anoxic bottom waters. The summer concentrations of nitrogen species of the reservoir are approximately 4 mg NOa -N/Iiter and 4 mg NH4-N/liter. 

A modeling of the fate of carbon from primary productivity to the final preservation in the sediment revealed a clear view that the today s E.M. environment will not produce a sapropel even if the bottom water was turned anoxic. The most important factor is most likely the intensity of the primary production, which must be in the order of 3-4 times higher than the present in combination with anoxic bottom water. This is also in agreement with the present situation in the Baltic Sea. 

Shale-normalized patterns quantify the extent of fractionation during periods of anoxia as illustrated by the water column data collected from different depths of Chesapeake Bay on 26 July 1988 (fig. 38). The oxic surface water exhibits a heavy-enrichment and large negative Ce anomaly while anoxic bottom water has an almost flat pattern and a small negative Ce anomaly. Hence the lanthanide composition shifts away from the heavy-enriched pattern of oxic seawater toward one that is more crust-like. As redox conditions become more reducing, the relative order of trivalent lanthanide release to the... 

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