Bottom-water oxygen

McConnaughey T (1989b) C and 0 disequilibrium in biological carbonates. II. In vitro simulation of kinetic isotope effects. Geochim Cosmochim Acta 53 163-171 McCorkle DC, Emerson SR (1988) The relationship between pore water isotopic composition and bottom water oxygen concentration. Geochim Cosmochim Acta 52 1169-1178 McCorkle DC, Emerson SR, Quay P (1985) Carbon isotopes in marine porewaters. Earth Planet Sci Lett 74 13-26... 

Figure 6. The degree of pyritization, defined as the fraction of reactive iron present as pyrite, is a measure of the extent to which available iron has reacted with sulfur (226). In lake sediments, iron monosulfides frequently are as abundant as pyrite and hence were included with pyrite in the values calculated for surface sediments from 13 lakes and presented here. Even this correction neglects Fe(II) that may have been reduced by sulfide but may be present as siderite. Availability of iron appears to be more important than bottom-water oxygenation in determining the degree of pyritization. In the right-hand graph, darkened squares represent sediments known to experience seasonal anoxia only the uppermost point experiences permanent anoxia. (Data are from references 30, 34, 56, and 61.)...

It has been suggested that sulfones represent a stable form of oxidized organic S (184). Because of a lack of analytical techniques, such forms have been tentatively identified in only two studies (32, 207). Additional data are needed to determine if the abundance of these forms can serve as an indicator of bottom-water oxygenation. 

The emergence of DS from sediments into stratified bottom waters has been shown to contribute significantly to bottom-water oxygen depletion in estuaries. 

As one approaches continents from the deep ocean, overlying productivity becomes greater and the water depth shoals so that particles are degraded less while sinking. Both factors increase the particulate organic matter flux to the sediment-water interface. This creates more extensive anoxia in the sediments, which is sometimes compounded on continental slopes by low bottom-water oxygen conditions. A natural... 

The most direct field evidence that the extent of sedimentary organic matter preservation is affected by exposure to bottom-water oxygen comes from oxidation fronts in deepsea turbidites of various ages and depositional settings (Wilson et al., 1985 Weaver and Rothwell, 1987). One of these deposits in which the timing of the exposure to oxic and anoxic conditions is well documented, is the relict f-turbidite from the Madeira abyssal plain (MAP) —700 km offshore... 

Gong C. and Hollander D. J. (1999) Evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction. Geochim. Cosmochim. Acta 63, 405 -411. 

Raiswell R., Buckley F., Berner R. A., and Anderson T. E. (1988) Degree of pyritization of iron as a paleoenviron-mental indicator of bottom-water oxygenation. J. Sedim. Petrol. 58(5), 812-819. 

Hines M. E., Eaganeh J., and Planinc R. (1997) Sedimentary anaerobic microbial biogeochemistry in the Gulf of Trieste, northern Adriatic Sea influences of bottom water oxygen depletion. Biogeochemistry 39, 65 - 86. 

In near-shore regions where organic matter flux to the sediments is high or bottom water oxygen concentrations are low and horizontal sediment transport does not dominate, sulfate reduction and subsequent methane formation are important processes. Early measurements of S04 and CH4 in marine porewaters indicated that methane appears only after most of the SO " has been reduced... 

The oxygen penetration depth in the ocean calculated from bottom water oxygen concentration and the particulate rain rate of organic matter to ocean sediments. Penetration depths less than I -2 cm are concentrated in the continental margin regions. From Morford and Emerson (1999). 

Deep seafloor communities are shaped by a number of key parameters that directly affect the nature and abundance of living organisms and their interactions with seafloor geochemistry. These parameters include (a) substratum type, (b) near-bottom hydrodynamic regime, (c) bottom-water oxygen concentration, (d) sinking particulate-organic-carbon (POC) flux, and (e) sediment redox conditions. Below, we describe these parameters and their variation in the northeastern abyssal Pacific. 

Although bottom-water masses are relatively old in the NEPAP, bottom-water oxygen concentrations remain well above 2mil-1 and hence they probably do not influence benthic community structure (Levin Gage, 1998). In the eastern tropical Pacific, oxygen-minimum zones appear in mid-water (100-1000m) due to intense water column decomposition but they do not extend to abyssal depths (Wishner etal., 1990). 

Fig. 6.19 Ratio of carbon oxidation by denitrification and oxic respiration as a function of bottom water oxygen content (after Canfield 1993).

In regions without limitation by bottom water oxygen depletion, as prevailing in large portions of the Southern and Northern Atlantic, Equation 6.14 can be simplified to... 

McCorkle, D.C., Emerson, S.R., 1988. The relationship between pore water carbon isotopic composition and bottom water oxygen concentration. Geochimica et Cosmochimica Acta 52 1169-1178. 

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