Mid-ocean ridges, hydrothermal vents

Bouman C, Vroon PZ, Elliott TR, Schwieters JB, Hamester M (2002) Determination of lithium isotope compositions by MC-ICPMS (Thermo Finnigan MAT Neptune). Geochim Cosmochim Acta 66 A97 Bray AM (2001) The geochemistry of boron and lithium in mid-ocean ridge hydrothermal vent fluids. PhD thesis. University of New Hampshire, 125 p... 

To relate the isotopic composition of marine calcium to variations in the calcium cycle requires characterization of the 5 Ca values of the sources and sinks of Ca to the oceans, and estimates of the Ca fluxes. Neither is well documented presently. Estimates of the calcium fluxes from Milliman (1993) are shown in Table 3. There are six analyses of 5 Ca from mid-ocean ridge hydrothermal vents, and these average -1-0.2 + 0.2 (Zhu and MacDougall... 

Bray A. M. and Von Damm K. L. (2003a) The role of phase separation and water—rock reactions in controlling the boron content of mid-ocean ridge hydrothermal vent fluids. Geochim. Cosmochim. Acta (in revision). 

Stable isotope (5 0, 5D summarized in Figure 18 from Alt et al. (1996). The important thing to take from this comprehensive data set is that the sheeted dike complex, especially the lower dikes, is representative of the deep reaction zone beneath a mid-ocean ridge hydrothermal vent... 

Fig. 2.2 Black smoker at a mid-ocean ridge hydrothermal vent. Credit OAR/National Undersea Research Program (NURP) NOAA...

Hydrothermal plumes are the water column manifestation of mid-ocean ridge hydrothermal activity (e.g. Baker etal., 1995). They form above areas of venting as a result of the buoyancy of the heated fluids as the fluids rise, they entrain ambient seawater, thus continuously increasing the plume volume until neutral buoyancy is achieved and the plume disperses laterally (Baker etal., 1995). These warm, buoyant plumes rise up to several hundred metres above the seafloor and extend for several kilometres away from vents [e.g. see reviews by Baker... 

Bowers TS (1989) Stable isotope signatures of water-rock interaction in mid-ocean ridge hydrothermal systems sulfur, oxygen, and hydrogen. J Geophys Res 94(B5) 5775-5786 Bowers TS, Campbell AC, Measures Cl, Spivack AJ, Khadem M, Edmond JM (1988) Chemical controls on the composition of vent fluids at 13°N-11°N and 21°N, East Pacific Rise. J Geophys Res 93 4522-... 

Haymon R. M., Fornari D. J., Edwards M. H., Carbotte S., Wright D., and Macdonald K. C. (1991) Hydrothermal vent distribution along the East Pacific Rise crest (9°09 -54 N) and its relationship to magmatic and tectonic processes on fast-spreading mid-ocean ridges. Earth Planet. Sci. Lett. 104, 513-534. 

Fig. 8.1 Diagram illustrating the major geochemical and microbial processes associated with seawater circulation in the crust and hydrothermal activity at mid-ocean ridges. Not all processes or features are found at all hydrothermal vent sites. Diagram not to scale (see text for further details).

Evidence for a subsurface biosphere at deep-sea hydrothermal vents Deming and Baross (1993) proposed the study of accessible black smokers and the ejecta of seafloor diking eruptive events (see below) as indirect windows to the subsurface. Since then, numerous studies have documented a variety of evidence supporting the existence of a subsurface biosphere below mid-ocean ridges, although the quantitative importance of this biosphere remains to be established (Kelley etal., 2002). 

Adiabatic-mixing pathways, where seawater (2°C) mixes into hydrothermal fluid (350°C), have been successfully used to model formation of sulfide minerals associated with venting hydrothermal solutions at mid-ocean ridges (9). Sulfate reduction can be quantitatively and isotopically important in such reactions (. Combinations of three types of isotopic path constraints discussed above have been examined, using the mixing reaction pathways calculated by Janecky and Seyfried ( ) for chemical equilibrium and initial sulfur isotopic compositions of 1 per mil for the hydrothermal solution and 21 per mil for seawater (Figure 1). 

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