15:45 〜 16:00
[SGC35-08] That other kind of oil; trans fatty acids and hydrogenation in the subseafloor hydrothermal system of Iheya Knoll
キーワード：Organic Geochemistry, Hydrothermal, IODP, fatty acid, resource provision
The hydrogenation sequence for fatty acids (that other kind of oil) involves several reactions with the formation of fully saturated fatty acids being the ultimate end-stage. In the context of “oil-upgrading” mixtures of mostly saturated n-alkanoic acids and cis isomers of alkenoic acids are the main feedstock. The trans isomers of alkenoic acids are not commonly de novo synthesised and instead are intermediate products of hydrogenation processes. Thus except where found in certain specifc cases (e.g. in ruminants such as cows and sheep), trans alkenoic acids can be considered markers for the operation of an abiotic hydrogenation processes.
IODP Expedition 331 (the Deep Hot Biosphere) collected subsurface samples of the Iheya North Hydrothermal system. Trans n-alkenoic acids are present in hydrothermally altered sediments of the Iheya Knoll hydrothermal field. They are not found exclusively at a single site, location or depth, but instead occur where favourable conditions permitted their transformation from cis precursors, but conditions did not enable conversion to fully saturated counterparts. When considered in the context of thermal maturity (combinations of time and temperature), the greatest proportion of trans n-alkenoic acids are found at medial levels of organic matter thermal alteration (a vitrinite reflectance equivalence of 0.7 to 0.9 %VRE). Fully saturated alkanoic acids predominate in the most thermally altered sediments. (VRE > 0.9 %) Therefore, as is the case for industrial hydrogenation, trans fatty acids are intermediaries in the thermal alteration of fatty acids in hydrothermal systems.
This strongly indicates that subseafloor hydrothermal processes at Iheya Knoll emulates to at least some degree an important industrial process used by society to upgrade non-petroleum oils. Based on what is known from industrial hydrogenation, this is likely a result of high temperatures, high water pressures, hydrogen availability and an open system with reactive-surfaces that can catalyse processes. As society looks for sustainable sources of essential materials to support modern standards of living, it could be beneficial to identify natural systems that can not only provide energy but also other things needed for manufacture. In the case of the Iheya field the quantities of fatty acid are low, and the process is sub-optimal compared to an optimised industrial process, but the other necessary components such as elemental feedstocks (hydrogen) and catalytic surfaces (phyolosilicates) are present. Consequently, if the natural system was supplied with the material that needed to be hydrogenated, such a hydrothermal system could be used to perform this industrial process. From a proof of concept point of view, the stepwise hydrogen of fatty acids at Iheya North hydrothermal field demonstrate that this is reasonable.
Humans have a long history of utilising circumstantially favourable biological processes and systems to upgrade key materials with examples being fermentation and nitrification. By contrast geological processes and systems have mostly only be used or researched only as energy sources, or to explore for mineral resources. The trans fatty acids at Iheya North hydrothermal field demonstrate that this need not be the case and that there exists geological systems and processes that circumstantially possess key elements of important processes. In this case step-wise hydrogenation via the provision of heat, hydrogen, and catalytic surfaces in a hydrothermal system.
IODP Expedition 331 (the Deep Hot Biosphere) collected subsurface samples of the Iheya North Hydrothermal system. Trans n-alkenoic acids are present in hydrothermally altered sediments of the Iheya Knoll hydrothermal field. They are not found exclusively at a single site, location or depth, but instead occur where favourable conditions permitted their transformation from cis precursors, but conditions did not enable conversion to fully saturated counterparts. When considered in the context of thermal maturity (combinations of time and temperature), the greatest proportion of trans n-alkenoic acids are found at medial levels of organic matter thermal alteration (a vitrinite reflectance equivalence of 0.7 to 0.9 %VRE). Fully saturated alkanoic acids predominate in the most thermally altered sediments. (VRE > 0.9 %) Therefore, as is the case for industrial hydrogenation, trans fatty acids are intermediaries in the thermal alteration of fatty acids in hydrothermal systems.
This strongly indicates that subseafloor hydrothermal processes at Iheya Knoll emulates to at least some degree an important industrial process used by society to upgrade non-petroleum oils. Based on what is known from industrial hydrogenation, this is likely a result of high temperatures, high water pressures, hydrogen availability and an open system with reactive-surfaces that can catalyse processes. As society looks for sustainable sources of essential materials to support modern standards of living, it could be beneficial to identify natural systems that can not only provide energy but also other things needed for manufacture. In the case of the Iheya field the quantities of fatty acid are low, and the process is sub-optimal compared to an optimised industrial process, but the other necessary components such as elemental feedstocks (hydrogen) and catalytic surfaces (phyolosilicates) are present. Consequently, if the natural system was supplied with the material that needed to be hydrogenated, such a hydrothermal system could be used to perform this industrial process. From a proof of concept point of view, the stepwise hydrogen of fatty acids at Iheya North hydrothermal field demonstrate that this is reasonable.
Humans have a long history of utilising circumstantially favourable biological processes and systems to upgrade key materials with examples being fermentation and nitrification. By contrast geological processes and systems have mostly only be used or researched only as energy sources, or to explore for mineral resources. The trans fatty acids at Iheya North hydrothermal field demonstrate that this need not be the case and that there exists geological systems and processes that circumstantially possess key elements of important processes. In this case step-wise hydrogenation via the provision of heat, hydrogen, and catalytic surfaces in a hydrothermal system.