Final Activity Report Summary - HYDRAMED (Geological assessment of gas hydrates in the Mediterranean Sea)
Gas hydrates are ice-like compounds that form naturally within deep-marine sediments, concentrating gases (mainly methane). An understanding of their formation and release over time in a given area is of broad scientific and social interest, due to their impacts on global climate, on slope stability and on resource evaluations. HYDRAMED is a project to address the gas hydrate system in the Mediterranean Sea. The intention of the project was to seek a regional understanding of the possible present and past occurrence of hydrates, over glacial-interglacial timescales, so as to establish a context for more detailed research initiatives. The means of achieving this was a combination of modelling of the hydrate stability zone (HSZ) to guide observations in areas of interest.
These actitivies led to the following results:
* modelling confirms that the hydrate stability zone (for methane) is present throughout the Mediterranean Sea, at relatively great depths (>1 km) due to high bottom water temperatures, but in significant thicknesses (>200 m) only in the eastern Mediterranean basins, due to lower geothermal gradients.
* the stability zone increases in thickness and extent if methane is accompanied by higher hydrocarbons, but model results show that gas composition was a less important influence on hydrate stability in the Mediterranean than high pore water salinities, which can locally eliminate the HSZ above the Messinian evaporitic succession.
* quantitative comparison of the thickness of the HSZ with an isopach of Plio-Quaternary sediments in the Mediterranean shows that the base of the stability zone lies above the Messinian evaporitic succession in most areas (and so would be able to generate bottom simulating seismic reflectors, or BSRs,), but that this is not the case along the Mediterranean Ridge accretionary prism (where BSRs are therefore not expected).
* changes in bottom water temperatures during glacial-interglacial cycles have had a strong impact on hydrate stability in the Mediterranean, with evidence of cooler bottom waters during glacial stages (by at least 4 Degrees Celsius) implying the HSZ to have been up to twice as thick and its upper limit hundreds of metres shallower along basin margins.
* several areas of interest for possible hydrate occurrence are identified, based on the coincidence of a thicker stability zone (>100 m) with evidence of seabed seepage of gas or gas-rich fluids and/or with geological conditions conducive to a supply of gas, e.g. the absence of thick Messinian salts (along basin margins), convergent tectonism and/or relatively thick Plio-Quaternary sediments.
* possible geochemical or geophysical indicators of hydrates are recognised in several locations based on observations using two pan-Mediterranean datasets, of deep-sea drillsites and multichannel seismic profiles; nowhere did both data types mutually support the presence of hydrates and only one area of interest is considered to provide strong indications (the Nile Fan, based also on industry data).
* one area of interest was the focus of a month-long acquisition campaign, as a collaboration with the EC-HERMES project, that resulted in a large geophysical dataset and the discovery of mud volcanoes associated with the flow of subjacent fluids and gases that may be linked to hydrates.
Taken as a whole, the project has yielded three main achievements:
1. a significantly improved understanding of the potential gas hydrate stability zone in the Mediterranean Sea and the factors controlling its varying extent and thickness over glacial-interglacial timescales, including regional variations in geothermal gradients and pore water salinities and temporal variations in bottom water temperatures.
2. the establishment of a regional context for more detailed research into hydrate occurrence, through the identification of several areas of interest.
3. participation in the discovery and exploration of a new province of cold seep features, including mud volcanoes, on the Calabrian Arc accretionary prism, during a joint HERMES-HYDRAMED IONIO leg.
These actitivies led to the following results:
* modelling confirms that the hydrate stability zone (for methane) is present throughout the Mediterranean Sea, at relatively great depths (>1 km) due to high bottom water temperatures, but in significant thicknesses (>200 m) only in the eastern Mediterranean basins, due to lower geothermal gradients.
* the stability zone increases in thickness and extent if methane is accompanied by higher hydrocarbons, but model results show that gas composition was a less important influence on hydrate stability in the Mediterranean than high pore water salinities, which can locally eliminate the HSZ above the Messinian evaporitic succession.
* quantitative comparison of the thickness of the HSZ with an isopach of Plio-Quaternary sediments in the Mediterranean shows that the base of the stability zone lies above the Messinian evaporitic succession in most areas (and so would be able to generate bottom simulating seismic reflectors, or BSRs,), but that this is not the case along the Mediterranean Ridge accretionary prism (where BSRs are therefore not expected).
* changes in bottom water temperatures during glacial-interglacial cycles have had a strong impact on hydrate stability in the Mediterranean, with evidence of cooler bottom waters during glacial stages (by at least 4 Degrees Celsius) implying the HSZ to have been up to twice as thick and its upper limit hundreds of metres shallower along basin margins.
* several areas of interest for possible hydrate occurrence are identified, based on the coincidence of a thicker stability zone (>100 m) with evidence of seabed seepage of gas or gas-rich fluids and/or with geological conditions conducive to a supply of gas, e.g. the absence of thick Messinian salts (along basin margins), convergent tectonism and/or relatively thick Plio-Quaternary sediments.
* possible geochemical or geophysical indicators of hydrates are recognised in several locations based on observations using two pan-Mediterranean datasets, of deep-sea drillsites and multichannel seismic profiles; nowhere did both data types mutually support the presence of hydrates and only one area of interest is considered to provide strong indications (the Nile Fan, based also on industry data).
* one area of interest was the focus of a month-long acquisition campaign, as a collaboration with the EC-HERMES project, that resulted in a large geophysical dataset and the discovery of mud volcanoes associated with the flow of subjacent fluids and gases that may be linked to hydrates.
Taken as a whole, the project has yielded three main achievements:
1. a significantly improved understanding of the potential gas hydrate stability zone in the Mediterranean Sea and the factors controlling its varying extent and thickness over glacial-interglacial timescales, including regional variations in geothermal gradients and pore water salinities and temporal variations in bottom water temperatures.
2. the establishment of a regional context for more detailed research into hydrate occurrence, through the identification of several areas of interest.
3. participation in the discovery and exploration of a new province of cold seep features, including mud volcanoes, on the Calabrian Arc accretionary prism, during a joint HERMES-HYDRAMED IONIO leg.