Hydrothermal marine environments

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, 

2-line ferrihydrite particles arranged in 2-300nm long chains were detected at the site of a hydrothermal vent (5-50 °C) on the Southern Explorer Ridge in the NW Pacific at a depth of ca. 1800m. Here, bacterial surfaces were suggested as the substrate for mineral nucleation (Fortin et al. 1998). 

It is obvious from these experiments that the absorption spectrum of the Martian red surface can be simulated reasonably well by a non-unique variety of Fe rich phases or their mixtures as can the weak magnetism, so that a positive identification will probably only be possible, following further in situ analyses and/or sample return and analysis in the lab.Two Mars Exploration Rovers (MERs) are due to arrive at Mars in 2004 and will attempt to analyze rocks and soils on the surface using several small spectrometers, including PanCAM (an extended visible region spectrometer), MiniTES (a thermal emission spectrometer), APXS (alpha proton X-ray spectrometer measuring the major elements), Mossbauer (run at current local temperature), as well as a 5-level magnet array similar to that on-board the Pathfinder Lander. 

As for soils, similar chemical extraction methods have been developed to determine the speciation of Fe in sediments (Heron et al. 1994 Kostka and Luther III, 1994). For Fe oxides, some modifications of the scheme used in soils are needed. In particular, oxalate may not be applied if large amounts of Fe are present because in oxalate solution, Fe will catalyze the dissolution of better crystalline Fe oxides such as goethite and, therefore, the method will not be be specific for ferrihydrite. Fe bound in sulphides and carbonate is extracted by HCl prior to dithionite which, as in soils, extracts most of the Fe oxides. The latter can also be extracted by a Ti -EDTA solu- 

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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. 

Chlorine isotope compositions vary by up to 15%o (Chapter 7 Stewart and Spivack 2004). These large variations in Cl isotope compositions are found in marine environments, including mid-ocean ridge basalts, seafloor and hydrothermal alteration products, and sedimentary pore... 

Hematitic iron ores of hydrothermal-sedimentary origin and Palaeozoic in age, are those of the Lahn-Dill-type in West and Central Europe (Harder, 1964). Hydro-thermal solutions associated with submarine volcanic activities have transported Fe (as FeCl3) into a marine environment, where after hydrolysis, hematite was formed (via ferrihydrite) at the margin of the basin, whereas siderite (after reduction) was formed in its centre. These ores are - in contrast to true sedimentary ores - low in Al,Ti and trace elements, which betrays their volcanic origin. 

The study of sulfide metabolism at hydrothermal vents dictated the development of methods that could process hundreds of samples which contain complex mixtures of sulfur compounds in a variety of blood, seawater and tissues samples. In addition, we needed the capability of using "S-radiolabeled compounds for the tracing of complex sulfur metabolic pathways in bacteria and animal compartments of the different hydrothermal vent symbioses. In some instances, in situ sampling by submersibles at depths of 2500 meters with associated recovery times of two hours necessitated the remote derivatization of samples at depth prior to recovery. None of the above methods completely met our needs. We have adapted the bimane-HPLC method (24.351 for shipboard use and have found it a particularly robust method for studying a number of questions concerning the role of reduced sulfur compounds in the marine environment. 

Normally weathered (subaerial, surface alteration) basalts can contain nontronite (a ferric smectite) and celadonite which form at the same time but by pseudomorphism of different basalt mineral grains during intermediate stages of alteration (i.e., between rock and soil) as summarized by Righi and Meunier (1995). These observations would lead one to beheve that celadonite can be formed in terrestrial environments. If so, celadonite is not entirely restricted to relatively low-temperature hydrothermal formations in marine environments. It does not, apparently, form a significant mixed layer mineral series with smectite minerals as do glauconite and ilhte. 

Many of these reactions are in the direction needed to close the marine mass balances for major ions (Fig. 2.4). The exceptions are that they supply an unnecessary additional siiik for SO4 (CaSO precipitation) and a vast additional source of K+. The additional sink for SO4 does little damage to the marine SO4 mass balance in Fig. 2.4 because its removal affects ordy Ca + and only at the level of about 15% of the Ca + riverine inflow. The hydrothermal source for K+ cannot be rationalized as easily, because there is no adequate sink in the marine environment. Research into the sources and sinks of alkali metals reveals that K+ (and other alkali metals) that are released from basalts at high temperature are reincorporated back into basaltic rock on the sea floor at low temperature. Thus, is recycled in the vicinity of hydrothermal vents. The rates of release and incorporation are uncertain enough to obscure whether the net K+ flux is into or from the ocean in these regions. It is possible that the low-temperature removal of K+ to basalt represents a net sink large enough to accommodate the river inflow. 

Injection of HCl from the hydrothermal weathering into marine water as well as dissolution of atmospheric SO2 steadily transformed the ocean s pH value from alkaline to acid. About 1 billion years ago the primitive soda Ocean was transformed into present salt sea. On other side, the changes in pH and possibly Eh have significantly altered the marine environment. This related mainly to carbonate system, which switched from sodium- to calcium- and magnesium-dominated mineral equilibrium about 1 billion years ago (Degens, 1989). 

However, amino acids are unlikely to form themselves into polymers without the help of some form of catalyst (Bada, 2004). Possible natural catalysts are mineral surfaces such as in the regular, repeating structure of clays although once bound to a clay the polymer has to be released. This is achieved in the laboratory with salt solutions and may, in nature, reflect an evaporative marine environment. An alternative venue is at hydrothermal vents where peptide bond formation is favored, and where catalysis may take place on sulfide mineral surfaces (Bada, 2004). Such a process has been described by Holm and Charlou (2001) who found linear saturated hydrocarbons with chain lengths of 16 to 29 carbon atoms in high-temperature hydrothermal fluids from a vent in the Mid-Atlantic Ridge. 

Most of the above diagenetic processes can occur in any of three environments. In the marine environment, the deposit is in contact with sea-water, which contains dissolved magnesium and may be either un-saturated, or super-saturated with respect to calcium carbonate species. In the ground-water environment, it is in contact with water, which is low in dissolved magnesium and is generally unsaturated with calcium carbonate. In the burial environment it is subject to high pressures and possibly elevated temperatures (or hydrothermal conditions) and is in contact with water, which may have a widely varying composition. 

Nichols, C. A. M., Guezennec, J., Bowman, J. P. Bacterial exopolysaccharides from extreme marine environments with special consideration of the southern ocean, sea ice and deep sea hydrothermal vents a review. Marine Biotechnol 2005, 7(4), 253-271. 

Holm NG (1992) Why are hydrothermal systems proposed as a plausible environment for the origin of life In Holm NG (Ed.) Marine Hydrothermal Systems and the Origin of Life. Kluwer, Dordrecht Boston London, p 5 Holm NG, Andersson EM (2005) Astrobiologie 5 444 Holm NG, Andersson EM (1995) Planet Space Sci 43 153... 

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