Marine hydrothermal waters

Average seawater Residence time River water (Luce R.) Marine hydrothermal water Continental high pH hydrothermal Continental low pH hydrothermal... 

Seawater and marine pore fluids. As discussed above, the chlorine isotopic composition of modem seawater does not vary measurably. This is not surprising in light of its long residence hme (approximately 90 million years) and its conservative behavior in the water column. In contrast, marine pore fluids have been demonstrated to vary considerably. There is also the likelihood that hydrothermal fluids may be fractionated as a result of exchange with mineral phases, as phase separation under marine hydrothermal conditions does not appear to lead to measurable fractionation (e.g., Magenheim et al. 1995). However, to date no stable-chlorine isotopic compositions of marine hydrothermal fluids have been reported in the literature. 

A 2-line ferrihydrite deposit is also formed from hydrothermal fluids at 60-93 °C upon mixing with sea water near the coast of Amberlite Island, Papua New Guinea. The hydrothermal waters are rich in As which is almost completely captured by the ferrihydrite (50-60 g As/kg), thereby hindering the formation of better crystalline Fe oxides and also preventing any toxic effects on the marine biota (Pichler, et al. 1999 Pichler and Veizer, 1999 Rancourt et al. 2001). Spherical, lOnm-sized, Si-containing,... 

There are three environments on Earth where microbes have been identified with temperature tolerances in a range of 100°C to 121 °C, namely, submarine hydrothermal vents, the subterranean deep biosphere, and terrestrial hot springs (Table 4.1). The highest temperature tolerances (110-121 °C) are found in microbes from marine hydrothermal vents and the subterranean deep biosphere high pressures prevent these waters from boiling at 100 °C, the normal boiling point of water at 1.01 bar (1 atm) pressure. From terrestrial hot springs, microbes have been isolated that can tolerate temperatures up to 103°C (Table 4.1). 

Alt J. C. and Bach W. (2003) Alteration of oceanic crust subsurface rock—water interactions. In Energy and Mass Tranter in Marine Hydrothermal Systems (eds. P. Halbach, V. Tunnichffe, and J. Hein). DUP, Berlin, pp. 7—28. 

The other most likely explanation for the mass imbalance of major ions in Fig. 2.4 is that there are substantial fluxes of seawater into hydrothermal areas where the chemistries of dissolved constituents are amended by contact with basalt at high temperatures and pressures. This phenomenon is described here by first reviewing the most important chemical changes in hydrothermal waters, and then discussing what these changes mean in terms of fluxes to and from the ocean. We shall see that the chemical aspects of this question are pretty well understood. However, as is usual in marine chemistry, estimation of fluxes has proven to be more difficult. 

The highest content was found in formation waters at depths of 2-3 km, and in hydrothermal waters from 200-400 to 500-700 ppm. The content of silicic acid in some sodium carbonate-bicarbonate brines can be as high as 2 700 ppm at pH 10 (Jones et al. 1969). However, natural waters usually show a concentration of silicic acid considerably lower than the solubility limit of amorphous silica under the same conditions (Fournier and Rowe 1962 Table 3.5). Consequently, modern subsurface waters are undersaturated with respect to amorphous silica, while marine water is unsaturated also with respect to quartz (Fournier and Rowe 1977). 

Oceans comprise 96.8% of the Earth s near-surfece water and accordingly, completely dominate the REE mass balance in the global hydrosphere. A thorough review of the geochemistry of REE in natural waters can be found in Byrne and Sholkovitz. Most REE in both terrestrial and marine waters are derived ultimately from the upper continental crust and accordingly, normalization to average shale is most informative. One notable exception is that REE in marine hydrothermal fluids are derived ultimately from interactions with oceanic basalts. 

This handbook article combines an up-to-date tabulation of the lanthanide composition of the ocean with a description of lanthanide distributions in the context of physical, chemical and biogeochemical processes controlling these distributions. The focus of this chapter is water column biogeochemistry. While pore waters and hydrothermal waters will be considered in this article, the extensive literature on the lanthanide geochemistry of minerals and marine sediments will not be discussed. 

Lanthanide cycling in anoxic marine basins, pore waters and hydrothermal waters... 

In summary, extensive research has been carried out on the lanthanide geochemistry of marine hydrothermal vent systems. Lanthanides are good indicators of water/rock reactions between hydrothermal fluids and basalt, and reactions between Fe oxide particles and seawater. While the lanthanides undergo an active geochemical cycle in and above venting fluids, this cycle is not quantitatively significant with respect to river water fluxes and oceanic cycles and inventory. 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

The first substantive report of Li isotopes in any Earth materials (Chan and Edmond 1988) largely presaged what was to come in Li isotope research in the oceans. The interpretations therein, based on a handful of data from seawater, fresh and altered basalt, hydrothermal fluids and lake waters, laid out the foundation to what has come since, in terms of natural and laboratory-based studies of the marine geochemistry of Li isotopes. 

An especially intriguing pair of products obtained from marine organisms in recent years are Vent and Deep Vent DNA polymerase. These products are used in DNA research studies. Their special feature is that they are at least 10 times as efficient as other similar products in polymerase chain reactions because they can tolerate temperatures just below the boiling point of water, a characteristic that comparable research tools lack. Vent and Deep Vent DNA polymerases are obtained from the bacterium Thermococcus litoralis, which is found around deep-sea hydrothermal vents at the bottom of the ocean. 

Figure 6.2 Hydrothermal vents are cracks in the Earth s surface generally found within deep ocean waters. Hot magma enters the cracks and heats the icy water, allowing bacteria to grow and feed a vast array of marine life.

---