5 Scientific Knowledge and Challenges Related to Hydrogen
93
hydrocarbon polymerisation could be catalysed by the surface of metals (Fe-Ni alloy) or oxides (magnetite) present in hydrated oceanic peridotites. However, the
very low outputs (less than 0.04 % dissolved CO 2 transformed into methane), dependence on the catalyst concentration, possible contamination and catalysis of the
experimental reactor by the metal are some of the parameters that are difficult to
control, therefore limiting the application of experimental data in the natural environment. This opens up a vast area for experimental and analytical research.
Quantities of Natural Hydrogen
Due to the dilution and gradual breakdown of hydrogen released into the deep sea,
flux calculations and estimations of hydrogen and other hydrocarbon gases are
difficult to make. However, we know that the hydrogen concentration extracted
from a hydrothermal vent in the mantle is around 10–16 mM/kg. A hydrothermal
vent around 40 cm in diameter releasing fluid at a rate of 1 m/s injects around
1 million m
3
of hydrogen a year into the water mass. By including all active, high
temperature vents within a site, and by taking into account all the related warm
diffusion areas, the hydrogen flux from serpentinization along the slow-spreading
Mid-Atlantic Ridge can be estimated at around 10
11
mol/year, with a range of estimations: 190 × 10
9
mol/year (Keir 2010), 167 × 10
9
mol/year (Cannat et al. 2010),
89 × 10
9
mol/year (Charlou et al. 2010).
The CH flux is estimated at around 84 × 10
9
mol/year by Emmanuel and Ague
(2007), 20 × 10
9
mol/year by Keir (2010), 25 × 10
9
mol/year by Cannat et al. (2010)
and 8 × 10
9
mol/year by Charlou et al. 2010.
However gas fluxes (H 2 , CH 4 ) from oceanic serpentinization remain poorly
known. The available data require confirmation by future studies. Nevertheless, it
is certain than slow-spreading ridges are a natural hydrogen source, indeed that is
not yet fully understood, but that represents a potential energy source that should be
considered in the Earth’s global energy balance.
Future Research Strategies
Currently, seven active sites producing large quantities of hydrogen have been discovered along the Mid-Atlantic Ridge between 8° S and Azores Triple Junction. Our
work shows that slow-spreading ridges have alternative natural hydrogen sources to
those derived from the burial and maturation of organic matter in sediment basins,
yet here this source is not mastered. What quantities of hydrogen and hydrocarbon gases are abiotically generated from the mineral ore? Estimations remain to be
made and can only be specified by continued exploration of slow-spreading ridges
and greater knowledge of the deep sea. Yet high hydrogen concentrations measured
in fluids on the seven active sites (Rainbow, Lost City, Ashadze 1 and 2, Logatchev
93
hydrocarbon polymerisation could be catalysed by the surface of metals (Fe-Ni alloy) or oxides (magnetite) present in hydrated oceanic peridotites. However, the
very low outputs (less than 0.04 % dissolved CO 2 transformed into methane), dependence on the catalyst concentration, possible contamination and catalysis of the
experimental reactor by the metal are some of the parameters that are difficult to
control, therefore limiting the application of experimental data in the natural environment. This opens up a vast area for experimental and analytical research.
Quantities of Natural Hydrogen
Due to the dilution and gradual breakdown of hydrogen released into the deep sea,
flux calculations and estimations of hydrogen and other hydrocarbon gases are
difficult to make. However, we know that the hydrogen concentration extracted
from a hydrothermal vent in the mantle is around 10–16 mM/kg. A hydrothermal
vent around 40 cm in diameter releasing fluid at a rate of 1 m/s injects around
1 million m
3
of hydrogen a year into the water mass. By including all active, high
temperature vents within a site, and by taking into account all the related warm
diffusion areas, the hydrogen flux from serpentinization along the slow-spreading
Mid-Atlantic Ridge can be estimated at around 10
11
mol/year, with a range of estimations: 190 × 10
9
mol/year (Keir 2010), 167 × 10
9
mol/year (Cannat et al. 2010),
89 × 10
9
mol/year (Charlou et al. 2010).
The CH flux is estimated at around 84 × 10
9
mol/year by Emmanuel and Ague
(2007), 20 × 10
9
mol/year by Keir (2010), 25 × 10
9
mol/year by Cannat et al. (2010)
and 8 × 10
9
mol/year by Charlou et al. 2010.
However gas fluxes (H 2 , CH 4 ) from oceanic serpentinization remain poorly
known. The available data require confirmation by future studies. Nevertheless, it
is certain than slow-spreading ridges are a natural hydrogen source, indeed that is
not yet fully understood, but that represents a potential energy source that should be
considered in the Earth’s global energy balance.
Future Research Strategies
Currently, seven active sites producing large quantities of hydrogen have been discovered along the Mid-Atlantic Ridge between 8° S and Azores Triple Junction. Our
work shows that slow-spreading ridges have alternative natural hydrogen sources to
those derived from the burial and maturation of organic matter in sediment basins,
yet here this source is not mastered. What quantities of hydrogen and hydrocarbon gases are abiotically generated from the mineral ore? Estimations remain to be
made and can only be specified by continued exploration of slow-spreading ridges
and greater knowledge of the deep sea. Yet high hydrogen concentrations measured
in fluids on the seven active sites (Rainbow, Lost City, Ashadze 1 and 2, Logatchev