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Abundant methane seepage and its impact on climate at the end of the last glaciation


The respected scientific journal Nature Communications published recently the article  “Timescales of methane seepage on the Norwegian margin following collapse of the Scandinavian Ice Sheet” co-authored by the scientists of the Institute of Geology at Tallinn University of Technology and the Department of Geology at the University of Tartu in cooperation with their colleagues at the Geological Survey of Norway, British Geological Survey and oil company Lundin Petroleum.

The article written with the participation of the researchers of the Institute of Geology at TUT Aivo Lepland and Tõnu Martma gives an overview of the seabed survey carried out by an international research team in the Barents Sea, north of Norway, as a result of which emissions of methane from sediments below the seafloor were dated and their impact on Earth’s climate was assessed.

The project leader Aivo Lepland, said,  “Methane that moves upward from the deep rock strata may, under conditions of high pressure and low temperature, be stored as an ice-like substance called methane hydrate in sediments below the seafloor . Methane hydrate formation in marine areas is particularly common during glaciations, when the glacier exerts great pressure on the seabed. The research of our research team showed that when the ice sheet disappeard, from the Barents Sea, the methane hydrate became unstable and melted; causing methane seepage toward the seafloor.” Methane oxidises just below the seafloor upon contact with sulphate dissolved in sediment porewater. As a result, carbonate crusts are formed, which can be dated by using radioactive isotopes. Dating of the crust samples from the Barents Sea indicated that these formed  from 17,000 to 7,000 years ago.  Since the carbonate crusts can be directly associated with methane seepage across the seafloor, the results obtained can be used for tracking the timescale of methane seepage. “It was established in the Laboratory of the Department of Isotope-paleoclimatology of the Institute of Geology at TUT that the methane that formed carbonate crusts came from methane hydrates,” Lepland added.

Data on the carbonate crusts from the Barents Sea tell us that as ice retreated from the  area at the end of the last glaciation (approximately 17,000 years ago), the methane hydrates melted and the methane emissions occurred over a protracted period of approximately 10,000 years. At 7,000 years ago the emissions largely stopped as new equilibrium under lower pressure and higher temperature at the seafloor was reached. This is also evidenced by millions of pockmarks (approximately 100 m diameter circular depressions, resulting from focussed gas release), which are currently inactive. Although substantial amount of methane was released at the seafloor during the abovementioned 10,000 year period, the studies on earth’s climate after the last glaciation have not established a significant influence on the climate that could be associated with methane hydrate melting. This could be explained by the fact that the methane hydrate melting is a relatively slow process.

Aivo Lepland said, “Methane is a strong greenhouse gas. Today, the global warming may cause melting of methane hydrates and release of methane to the atmosphere, which in turn can aggravate the greenhouse effect. It is uncertain, however, how fast the hydrate melting will occur and this requires further research.”

Nature Communications is among the world’s top scientific journals; it has been published since 2010, with coverage that includes topics in physics, chemistry, Earth sciences and biology. Articles of Estonian scientists have been published in the journal on average once a year.

Additional information:

Aivo Lepland
Marine geologist and researcher at the Geological Survey of Norway, also affiliated with the Institute of Geology at Tallinn University of Technology, and the Department of Geology at the University of Tartu.

Original article published by Tallinn University of Technology

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