Subglacial methane sources and sinks – an isotopic approach

Subglacial methane sources and sinks – an isotopic approach

Issued: Tue, 27 Feb 2018 14:00:00 GMT

SUERC Seminar Series

27 February

Subglacial methane sources and sinks – an isotopic approach

Peter Wynne, University of Lancaster

Glaciers and ice sheets have been suggested to serve as an impermeable ‘cap’ on the Earth’s surface, beneath which conditions of pressure, temperature and the presence of organic matter form the perfect cocktail for the production and entrapment of methane from biogenic and geological sources. During disintegration of the overburden ice mass through climatic warming, instability of sub-cap methane reserves are suggested to control the release of natural methane emissions to the atmosphere.

However, progress in understanding the role of glaciers and ice sheets in methane generation is currently based solely on pressure-temperature relationships, biological rates of methane production from laboratory investigations and observations of seeps beyond the ice margin. There is a lack of direct field based evidence from contemporary ice masses, and therefore a lack of scientific consensus regarding the role of glaciers and ice sheets in contributing to the methane budget.

Here, we present direct field based evidence of methane release from beneath a contemporary Icelandic glacier. Despite Icelandic glaciers typically overlying active geothermal zones, isotopic signatures suggest methane production is predominantly biogenic. The estimated annual flux of methane from beneath this single glacier (approximately 11,000 tonnes per year) is sufficient to rival the methane output obtained through total European subaerial geothermal and volcanic degassing.

Area-weighting this flux provides an output which is equivalent to wetland methane emissions across a variety of regions and habitats. This raises the distinct possibility that other valley glaciers containing ice at the pressure melting point may generate biogenic methane in-situ at the ice bed interface. Providing conditions of low redox status enable the transport of methane to the glacier snout, ice of temperate or polythermal regime may be able to contribute significant quantities of methane to the bottom-up inventory.

Techniques associated with field sampling of methane gases, including development of a mobile methane laboratory and the possibility of using clumped isotope analysis to distinguish between methane sourced under differing thermal conditions will also be discussed.

Glaciers and ice sheets have been suggested to serve as an impermeable ‘cap’ on the Earth’s surface, beneath which conditions of pressure, temperature and the presence of organic matter form the perfect cocktail for the production and entrapment of methane from biogenic and geological sources. During disintegration of the overburden ice mass through climatic warming, instability of sub-cap methane reserves are suggested to control the release of natural methane emissions to the atmosphere. However, progress in understanding the role of glaciers and ice sheets in methane generation is currently based solely on pressure-temperature relationships, biological rates of methane production from laboratory investigations and observations of seeps beyond the ice margin. There is a lack of direct field based evidence from contemporary ice masses, and therefore a lack of scientific consensus regarding the role of glaciers and ice sheets in contributing to the methane budget. Here, we present direct field based evidence of methane release from beneath a contemporary Icelandic glacier. Despite Icelandic glaciers typically overlying active geothermal zones, isotopic signatures suggest methane production is predominantly biogenic. The estimated annual flux of methane from beneath this single glacier (approximately 11,000 tonnes per year) is sufficient to rival the methane output obtained through total European subaerial geothermal and volcanic degassing. Area-weighting this flux provides an output which is equivalent to wetland methane emissions across a variety of regions and habitats. This raises the distinct possibility that other valley glaciers containing ice at the pressure melting point may generate biogenic methane in-situ at the ice bed interface. Providing conditions of low redox status enable the transport of methane to the glacier snout, ice of temperate or polythermal regime may be able to contribute significant quantities of methane to the bottom-up inventory. Techniques associated with field sampling of methane gases, including development of a mobile methane laboratory and the possibility of using clumped isotope analysis to distinguish between methane sourced under differing thermal conditions will also be discussed.