Fig 3 - uploaded by Cecile Konn
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A. Location map of the Atlantis Massif at 30°N along the Mid-Atlantic Ridge (MAR). The white box indicates the location of the Lost City Hydrothermal Field on the southern ridge of the massif. B. Southern wall of the Atlantis Massif. The white box shows the areal extent of the Lost City vent field, located on a terrace of the southern wall. From Kelley et al. (2005), Science, 307, p 1428.
Source publication
Natural gas, primarily methane (CH4), is produced in substantial amounts in ultramafic-hosted hydrothermal systems. These systems could also generate oil (heavier hydrocarbons) and the first building blocks of life (prebiotic molecules). In the presence of iron bearing minerals, serpentinisation reactions generate H2. Subsequently, CH4 could be syn...
Contexts in source publication
Context 1
... first hydrothermal system located on such an outcrop was identified in 1993 along the slow- spreading MAR. The Logatchev hydrothermal field was the first ultramafic-hosted vent area to be discovered of a series of five known today: Logatchev ( Batuev et al., 1994), Rainbow, Ashadze (Serpentine-Cruise-Ifremer, 2007), Lost City ( Kelley et al., 2001) and Nibelungen (Melchert et al., 2008) (Figure 3). The composition of the crust lying underneath those systems appears to be highly heterogeneous, unlike the basalt crust hosting mafic systems, and a well- constrained model has not yet been established. ...
Context 2
... Rainbow hydrothermal field is located on the Mid-Atlantic Ridge (MAR), south of the Azores at 36°14'N, 33°54'W at a 2300 m depth (Figure 3, Table 1) (German et al., 1996;Bougault et al., 1998;). It stands on the west-facing flank of the Rainbow ridge at the northeastern corner at the intersection between the Azores Mid-Atlantic Ridge (AMAR) segment and the south AMAR segment being also the intersection of the non-transform fault system and the ridge faults. ...
Context 3
... hydrothermal activity is concentrated at the southern edge of the Atlantis Massif located 15 km west of the MAR axis at 30°07N, 42°07W (Figure 3, Table 1). The massif rises to 700 m below the sea surface, is terminated in the south by the Atlantis transform fault, and is bounded to the East by a nodal basin that is down to 6000 m deep (Figure 7). ...
Context 4
... features about the Lost City hydrothermal system are its off-axis position, the low-temperature and high pH fluids, and the carbonate-brucite hydrothermal chimneys. The hydrothermal activity is concentrated at the southern edge of the Atlantis Massif located 15 km west of the MAR axis at 30°07N, 42°07W (Fig. 3). The massif rises at 700 m below the sea surface and is terminated in the south by a nodal basin that is up to 6000 m deep. The latter is formed by the intersection of the Atlantis Fracture Zone and the MAR ( Kelley et al., 2005). The field, which extends over 400 m in length, is composed of active, inactive, and fissure-filling ...
Citations
... SBSE was particularly suitable for this study which aimed at obtaining a broad qualitative overview of the organic composition of the resulting solutions after thermal degradation of P. abyssi. Moreover, the extraction protocol followed in the present work (detailed in the next §) is strictly the same as that described by Konn et al. (2009) who also showed its qualitative repeatability for the analyses of hydrothermal fluids (Konn, 2009;Konn et al., 2009). The extraction rates of compounds, especially polar molecules, by SBSE are mainly affected by the pH and the presence of salts in the solution (Pfannkoch et al., 2001). ...
Experiments on hydrothermal degradation of Pyrococcus abyssi biomass were conducted at elevated pressure (40 MPa) over a 200-450 °C temperature range in sapphire reaction cells. Few organic compounds could be detected in the 200 °C experiment. This lack was attributed to an incomplete degradation of P. abyssi cells. On the contrary, a wide range of soluble organic molecules were generated at temperatures ≥ 350 °C including toluene, styrene, C₈-C₁₆ alkyl-benzenes, naphthalene, C₁₁-C₁₆ alkyl-naphthalenes, even carbon number C₁₂-C₁₈ polycyclic aromatic hydrocarbons, C₁₅-C₁₈ alkyl-phenanthrenes and C₈:₀-C₁₆:₀ n-carboxylic acids. The effect of time on the final organic composition of the degraded P. abyssi solutions at 350 °C was also investigated. For that purpose the biomass was exposed for 10, 20, 60, 90, 270 and 720 min at 350 °C. We observed a similar effect of temperature and time on the chemical diversity obtained. In addition, temperature and time increased the degree of alkylation of alkyl-benzenes. This study offers additional evidence that a portion of the aliphatic hydrocarbons present in the fluids from the Rainbow ultramafic-hosted hydrothermal field may be abiogenic whereas a portion of the aromatic hydrocarbons and n-carboxylic acids may have a biogenic origin. We suggest that aromatic hydrocarbons and linear fatty acids at the Rainbow site may be derived directly from thermogenic alteration of material from the sub-seafloor biosphere. Yet we infer that the formation and dissolution of carboxylic acids in hydrothermal fluids may be controlled by other processes than in our experiments.
Between 12° and 40°N on the Mid-Atlantic Ridge (MAR), high- or
low-temperature hydrothermal activity and mantle degassing are
indicative of ongoing serpentinization process. Chemical composition of
fluids from ultramafic-hosted hydrothermal fields (Rainbow, 36°14'
N; Lost City, 30°N Logatchev I and II, 14°45' N; Ashadze I and
II, 12°58' N), all located along the MAR is compared here. The
uniformity in end-member major, minor element concentrations, and gas
contents suggest that, at each ultramafic field, all vented fluids are
issued from a nearly identical source. In all cases, vent fluids show
low H2S content (<1 mmol kg-1), extraordinary
high H2 (10 to 26 mmol kg-1) end-member
concentrations compared to basalt-hosted fluids. Hydrogen production
represents between 40% to 80% of the total extracted gas volume. The
total hydrogen discharge ΦH2 is found to be between 2.5
to 7.5 million standard cubic meters per year for the Rainbow single
site. Based on Rainbow H2/3He and
3He/heat ratios, a global H2 flux for slow
spreading ridges of 2 × 109 m3 STP
a-1 is estimated. Like basalt-hosted fluids, the
ultramafic-hosted fluids are controlled by phase separation. But
everywhere, H2 content is extraordinarily enriched in low or
high chlorinity phases, demonstrating that the serpentinization process
is mainly responsible for hydrogen production. As a consequence of the
high reducing power of these systems, isotopic measurements of light
hydrocarbons show that abiogenic hydrocarbons are generated by
Fischer-Tropsch type reaction. The serpentinization of ultramafics is a
common feature occurring along the MAR and strongly contributes to the
whole budget of hydrogen and abiogenic methane on Earth.
