Hot vents

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. 

Independently, there was the discovery in 1979 of the richness of organic compounds in hydrothermal hot vents (see for example Holm et al., 1992, and Chapter 3). The idea was fully developed by Wachtershauser (1988) and Cairns-Smith et al. (1992), and (of course) became another world. Life then began with the reduction of CO2 and N2 coupled with the reducing power of pyrite formation - and so was born the iron-sulfur-world hypothesis. Thus, the work of Wachtershauser also represents a link between the field of surface catalysis and the field of hydrothermal vents. 

The theory is based on the autotrophic metabolism of low-molecular-weight constituents in an environment of iron sulfide and hot vents. Figure 2.4 gives an illustration of one reaction pathway. It is worthwhile to consider that the metabolism is a surface metabolism, namely with a two-dimensional order, based on negatively charged constituents on a positively charged mineral surface. Actually Wachtershauser sees this as an interesting part of a broader philosophical view (Huber and Wachtershauser, 1997). 

A large number of successful experimental studies which tried to work out plausible chemical scenarios for the origin of life have been conducted in the past (Mason, 1991). A sketch of a possible sequence of events in prebiotic evolution is shown in Figure 3. Most of the building blocks of present day biomolecules are available from different prebiotic sources, from extraterrestrial origins as well as from processes taking place in the primordial atmosphere or near hot vents in deep oceans. Condensation reactions and polymerization reactions formed non-in-structed polymers, for example random oligopeptides of the protenoid type (Fox... 

Ogata Y, Imai E, Honda H, Hatori K, Matsuno K. Hydrothermal circulation of seawater through hot vents and contribution of interface chemistry to prebiotic synthesis. Orig. Life Evol. Biosph. 2000 30 527-537. 

Herzig P. M. and Hannington M. D. (2000) Input from the deep hot vents and cold seeps. In Marine Geochemistry (eds. H. D. Schultz and M. Zabel). Springer, Heidelberg, pp. 397-416. 

Standard rRNA molecular phylogeny (Woese, 1987 Barnes et al, 1996 Stetter, 1996 Pace, 1997) implies the antiquity of hyperthermophile organisms. Though there has been much dispute about the rRNA interpretation, there is some consensus that, whether or not it is the very most ancient, life around hot-water vents is certainly of great antiquity. The implication is that by mid-Archean, hyperthermophile habitats around hot vents were populated by microbial mats, and the waters around hot vents were occupied by free-swimming cells. Mesophile prephotosynthetic plankton probably existed in the open seas, and, distal to the thermophile life in the surroundings of vents, the mesophile habitats further from the hot springs were also occupied. 

For many years, one way to solve these drawbacks has been the identification and isolation of new biocatalysts with the desired characteristics. The most common procedure for isolation and identification of biocatalysts has also been applied to microbial populations living in harsh environments such as hot springs, abyssal hot vents or geothermal power plants. These microorganisms, known as extremophiles can be foimd in environments of extreme temperature, ionic strength, pH, pressure, metal concentrations or radiation levels. These natural reservoirs of extremozymes directly offer new activities and extreme stabilities but these microorganisms also offer novel metabolic pathways. Table 10.11 summarizes the identified extremoz5mies found in some extremophiles. 

For the sake of completeness, advective effusions also need to be mentioned here (see Chapters 13 and 14). Although their signifieanee for global balances of materials (e.g. CO, see Chapter 5) has been hardly investigated yet, the hot vents and cold seeps, usually locally confined, seem to be rather unimportant for the interaction described here. Nevertheless, they may be relevant when looking on specific element cycles (e.g. Li, B or Ba). 

Input from the Deep Hot Vents and Cold Seeps... 

If the hot vent lies in a depression such as the Atlantis II Deep in the Red Sea, the results of the hydrothermal reactions are very evident (see Figure 1). Water is removed together with magnesium and sulfate, and calcium is released from the basalt. Rock salt (NaCl), anhydrite (CaS04), and silica (SiOa) are formed and the brine becomes saturated with these solids. Sulfide metals are coprecipitated with iron sulfide (FeS). 

Hot Vent Radiation Level Analog 0to+4VDC Area Monitor... 

Orders of kingdom nanoarchaeota Found in hot vent off coast of Iceland... 

Little is known about the kingdoms korarchaeota and nanoarchaeota. Genetic characteristics indicate that they are distinct kingdoms (or phyla) from each other and from the other kingdoms of the Archaea. Both are thermophilous. The former was discovered in a terrestrial hot spring in Yellowstone National Park, USA, while the discovery of the latter in a hot vent off the coast of Iceland occurred in 2002. Huber et ai, (2002) report that it is a symbiont with a member of the igneococcales. 

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