Vents, ocean

See also Abyssal plain Coast and beach Hydrothermal vents Ocean zones Oceanography Sea level Seamounts Tides. 

Fig. 2. Distribution of ( ) known and (o) suspected metalliferous sulfide deposits and active hydrothermal vents in the Pacific Ocean (42).

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

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. 

Sulfur dioxide occurs in industrial and urban atmospheres at 1 ppb—1 ppm and in remote areas of the earth at 50—120 ppt (27). Plants and animals have a natural tolerance to low levels of sulfur dioxide. Natural sources include volcanoes and volcanic vents, decaying organic matter, and solar action on seawater (28,290,291). Sulfur dioxide is beHeved to be the main sulfur species produced by oxidation of dimethyl sulfide that is emitted from the ocean. 

The flow of hydrothermal solutions iato the oceans from hydrothermal vents, ie, springs coming from the sea floor ia areas of active volcanism, and the chemical reactions occurring there by high temperature alteration of basalts ate of significance ia the mass balance of and. Eurthermore,... 

There is some debate about what controls the magnesium concentration in seawater. The main input is rivers. The main removal is by hydrothermal processes (the concentration of Mg in hot vent solutions is essentially zero). First, calculate the residence time of water in the ocean due to (1) river input and (2) hydro-thermal circulation. Second, calculate the residence time of magnesium in seawater with respect to these two processes. Third, draw a sketch to show this box model calculation schematically. You can assume that uncertainties in river input and hydrothermal circulation are 5% and 10%, respectively. What does this tell you about controls on the magnesium concentration Do these calculations support the input/removal balance proposed above Do any questions come to mind Volume of ocean = 1.4 x 10 L River input = 3.2 x lO L/yr Hydrothermal circulation = 1.0 x 10 L/yr Mg concentration in river water = 1.7 X 10 M Mg concentration in seawater = 0.053 M. 

Rathgeber C, N Yurkova, E Stackebrandt, JT Beatty, V Yurkov (2002) Isolation of tellurite and selenite-resistant bacteria from hydrothermal vents of the Juan de Fuca Ridge in the Pacific Ocean. Appl Environ Microbiol 68 4613-4622. 

Butterfield, V.A., McDuff, R.E., Franklin, J. and Wheat, C.G. (1994) Geochemistry of hydrothermal vent fluids from Middle Valley, Juan de Fuca Ridge. In Mottl, M.J., Davis, E.E., Fi.sher, A.T. and Slack, J.F. (eds.). Proceedings of the Ocean Drilling Program. Sci. Proc., 139, 395-410. 

The discovery of hydrothermal vents on the ocean floor has led some biogenesis researchers to turn their attention to the hydrosphere (see Sect. 7.2) and to the processes occurring there at a depth of 2-3 km. 

The same problem, the stability of the nucleobases, was taken up by Levi and Miller (1998). They wanted to show that a synthesis of these compounds at high temperatures is unrealistic, and thus they took a critical look at the high temperature biogenesis theories, such as the formation of biomolecules at hydrothermal vents (see Sect. 7.2). The half-life of adenine and guanine at 373 K is about a year, that of uracil about 12 years and of the labile cytosine only 19 days. Such temperatures could have easily been reached when planetoids impacted the primeval ocean. 

In the same year, Miller and the biologist Antonio Lazcano (National Autonomous University of Mexico) spoke out against hypotheses that life could have originated at hydrothermal vents. They believe that the presence of thermophilic bacteria (the oldest life forms) does not prove that biogenesis occurred in the depths of the oceans. Stanley Miller sees a greater chance for successful pre-biotic chemistry under the conditions of a cold primeval Earth rather than at high temperatures in hydrothermal regions (Miller and Lazcano, 1995). 

The processes occurring at hydrothermal systems in prebiotic periods were without doubt highly complex, as was the chemistry of such systems this is due to the different gradients, for example, of pH or temperature, present near hydrothermal vents. Studies of the behaviour of amino acids under simulated hydrothermal conditions showed that d- and L-alanine molecules were racemised at different rates the process was clearly concentration-dependent. L-Alanine showed a low enantiomeric excess (ee) over D-alanine at increasing alanine concentrations. The same effect was observed with metal ions such as Zn2+ in the amino acid solution. Thus, homochi-ral enrichment of biomolecules in the primeval ocean could have resulted under the conditions present in hydrothermal systems (Nemoto et al., 2005). 

Were the first biomolecules formed in the primeval atmosphere or At hydrothermal vents in the depths of the primeval oceans or On the surface of the young Earth, at clay mineral surfaces or Via thioesters ... 

In this chapter, we develop geochemical models of two hydrothermal processes the formation of fluorite veins in the Albigeois ore district and the origin of black smokers, a name given to hydrothermal vents found along the ocean floor at midocean ridges. 

Where fluids discharge from hot springs and mix with seawater, they cool quickly and precipitate clouds of fine-grained minerals. The clouds are commonly black with metal sulfides, giving rise to the term black smokers. Some vents give off clouds of white anhydrite these are known as white smokers. Structures composed of chemical precipitates tend to form at the vents, where the hot fluids discharge into the ocean. The structures can extend upward into the ocean for several meters or more, and are composed largely of anhydrite and, in some cases, sulfide minerals. 

Subsea hydrothermal vents, as mentioned in the previous section, are sites of intense biological activity, relative to the rest of the ocean floor (e.g., Van Dover, 2000 Zierenberg et al., 2000). Life here ranges in complexity from single cells to higher forms such as tubeworms. The vent ecosystems are unique in many ways, including the fact that the primary producers create biomass not by photosynthesis, as is familiar in more accessible environments, but by chemosynthesis. 

Figure 14. Plot of Li isotopic composition vs. concentration of thermal waters from the continents and the oceans (see text for references). Differences between the isotopic range of marine versus non-marine fluids emphasizes the variability in 5 Li of continental rocks compared to oceanic basalt. The dilution of the continental fluids goes along with their lower temperatures vent fluids are the only truly geothermal samples here, with temperatures in excess of 300°C.

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... 

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