Ridge flank

James et al. (2003) inferred, on the basis of comparison between experimental results and natural data, that upwelling rate is another parameter that is critical to interpretation of Li isotope signatures of pore fluids. At low temperatures (<100°C), Li may be lost to fluids by sediments (Chan et al. 1994a). However, enrichment in Li of pore fluids to concentrations greater than that of seawater near basement contacts may more prevalently reflect slow rate of upwelling, as fluid-sediment interaction is thereby favored. This interpretation is consistent with data from a variety of samples from ridge flanks (e.g., Elderfield et al. 1999 Wheat and Mottl 2000). 

Wheat CG, Mottl MJ (2000) Composition of pore and spring waters from Baby Bare Global implications of geochemical fluxes from a ridge flank hydrothermal system. Geochim Cosmochim Acta 64 629-642 White DE, Thompson JM, Fournier RO (1976) Lithium contents of thermal and mineral waters. In Lithium Resources and Requirements by the Year 2000. Vine JD (ed) U.S. Geol Surv Prof Pap 1005 58-60 Xiao YK, Beary ES (1989) High-precision isotopic measurement of lithium by thermal ionization mass spectrometry. Int J Mass Spect Ion Proc 94 101-114... 

Matthews A, Zhu X-K, O Nions K (2001) Kinetic iron stable isotope fractionation between iron (—II) and (—III) complexes in solution. Earth Planet Sci Lett 192 81-92 McManus J, Nagler TE, Siebert C, Wheat CG, Hammond DE (2002) Oceanic molybdenum isotope fractionation Diagenesis and hydrothermal ridge-flank alteration. Geochem Geophys Geosys 3 2002GC000356... 

At all three sites, the six indirect indicators were found as listed in the Site 997 discussion. The similarity of the indicators in the three sites is exemplified by the chlorinity anomalies in the hydrate regions of Figure 7.22b. There is a minimum of approximately 1.4 vol%, 1.7% and 2.1% gas hydrate at Sites 994, 995, and 997, respectively assuming a low chlorinity baseline, and a sediment porosity of 50%. The amount of gas hydrate appears to increase from the ridge flank (Site 994) to the ridge crest (Site 997) with various indicators shown in Table 7.11. 

FIGURE 7.26 (See color insert following page 390.) Site 1245A southern Hydrate Ridge Flank logs (gammaray, density, Resistivity at Bit, and Archie water saturation). (T.S. Collett, Personal Communication, November 18, 2005, Leg 204, Scientific Party, 2005)... 

Lang, S. Q., Butterfield, D. A., Lilley, M. D., Johnson, H. D., and Hedges, J. I. (2006). Dissolved organic carbon in ridge-axis and ridge-flank hydrothermal systems. Geochim. Cosmochim. Acta 70, 3830-3842. 

Alt J. C., Teagle D. A. H., Laverne C., Vanko D. A., Bach W., Honnorez J., Becker K., Ayadi M., and Pezard P. A. (1996) Ridge flank alteration of upper oceanic crust in the Eastern Pacific synthesis of results fro volcanic rocks of holes 504B and 896A. Proc. ODP Sci. Results 148, 435-450. 

Wheat C. G. and Mottl M. J. (2000) Composition of pore and spring waters from Baby Bare global implications of geochemical fluxes from a ridge flank hydrothermal system. Geochim. Cosmochim. Acta 64(4), 629-642. 

Figure 13 Schematic representation of an MOR hydrothermal system and its effects on the overlying water column. Circulation of seawater occurs within the oceanic crust, and so far three types of fluids have been identified and are illustrated here high-temperature vent fluids that have likely reacted at >400 °C high-temperature fluids that have then mixed with seawater close to the seafloor fluids that have reacted at intermediate temperatures, perhaps 150 °C. When the fluids exit the seafloor, either as diffuse flow (where animal communities may live) or as black smokers, the water they emit rises and the hydrothermal plume then spreads out at its appropriate density level. Within the plume, sorption of aqueous oxyanions may occur onto the vent-derived particles (e.g., phosphate, vanadium, arsenic) making the plumes a sink for these elements biogeochemical transformations also occur. These particles eventually rain-out, forming metalliferous sediments on the seafloor. While hydrothermal circulation is known to occur far out onto the flanks of the ridges, little is known about the depth to which it extends or its overall chemical composition because few sites of active ridge-flank venting have yet been identified and sampled (Von Damm, unpublished).

Phosphorus and vanadium, which are typically present in seawater as dissolved oxyanion species, have been shown to exhibit systematic plume-particle P Fe and V Fe variations which differ from one ocean basin to another (e.g., Trefry and Metz, 1989 Feely et al., 1990). This has led to the hypothesis (Feely et al., 1998) that (i) plume P Fe and V Fe ratios may be directly linked to local deep-ocean dissolved phosphate concentrations and (ii) ridge-flank metalliferous sediments, preserved under oxic diagenesis, might faithfully record temporal variations in plume-particle P Fe... 

Maris C. R. P. and Bender M. L. (1982) Upwelfing of hydrothermal solutions through ridge flank sediments shown by pore-water profiles. Science 216, 623—626. 

Low-temperature ridge flank 0.65 Wheat et al. (1996) basalt seawater reactions during convective circulation of seawater in sediments and crust of flanks of MORs... 

Deep-sea vents have only been studied in the late twentieth century, so there is still much to learn in terms of their global contribution because of their inaccessibility. However, they can affect global fluxes, and some estimates would suggest that warm ridge-flank sites may remove each year, as much as 35% of the riverine flux of sulfur to the oceans (Wheat and Mottl, 2000). The hydrothermal vents are locally important sources of sulfide-containing materials. The black smokers yield polymetal sulfides, that will... 

C. G. Lilley, M. D. 1998. C02-depleted fluids from mid-ocean ridge-flank hydrothermal springs. Geochimica et Cosmochimica Acta, 62, 2247-2252. 

Estimates of water chemistry changes on the ridge flanks 55... 

A schematic representation of the categories of heat and water convection through the sediments and crust. Axiai (ridge crest) heat convection is divided into that from hlgh-temperature (c. 350 °C) and lower-temperature vents, and the rest is off-axis flow through the thin veneer of sediments on the ridge flank. 

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