Tectonic Stress Effects on Arctic Methane Seepage - SEAMSTRESS

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2019

End date

12/31/2023

Budget

977,973 EUR

Fundings

Abstract

The goal of the SEAMSTRESS project is to investigate the geological mechanisms that control the release of greenhouse gases from the ocean floor in the Arctic. Greenhouse gases, such as methane, are a major concern when it comes to climate change. Large amounts of these gases are released from the sediment on the ocean floor, not only potentially influencing our global climate, but also affecting seabed ecology and increasing the risk of underwater landslides and tsunamis. This is a widespread phenomenon that has been occurring for hundreds and even millions of years with periods of intensification. The SEAMSTRESS project is providing a deeper understanding of how glacial and mid-ocean ridge processes have influenced the timing and the amounts of gas release from Arctic margins. During the first half of the project, we have had a strong focus on collecting an exceptional amount of interdisciplinary data during expeditions onboard Norwegian research vessels R/V Helmer Hanssen and R/V Kronprins Haakon. In the summer in 2019 the first project experiment successfully collected, in collaboration with Geomar, seismic waves records from 21 seismometers placed around a spot where methane bubbles raise from the seafloor for more than 900 m toward the sea surface. The PhD students within the project are using seismometer and 3D seismic data recorded in the sea surface to reveal the faults and fractures that allow the release of methane into the ocean and the mechanisms that control the phenomenon. In fall 2019, a large expedition was conducted to collect long sediment cores (> 10 m length) for the study of the petrophysical properties of the sediment (e.g., density, permeability, strength, magnetic susceptibility, in-situ pressure and temperature). These data have revealed, among other things, that tides and small changes in the sea level are sufficient to trigger release of gas from shallow gas accumulation under deep waters along the west-Svalbard continental slope. Despite the unusual difficult times due to Corona, the project has developed continuously. In the summer in 2020 we successfully collected 7 seismometers that were recording seismicity around an active gas seepage area since last year. As part of the collaboration with the Alfred Wegener Institute, we placed 10 additional seismometers at the northern termination of the Knipovich mid-ocean ridge. In autumn 2020 Piezometer data (in-situ sediment pressure and temperature) were collected in collaboration with Ifremer on 4 key sites along the margin to study whether pore fluid pressure increases or decreases from the mid-ocean ridge towards the continental shelf off Svalbard. As part of the collaboration with the Alfred Wegener Institute (AWI), we placed 10 additional seismometers at the northern end of the Knipovich ridge. We pick-up these instruments from the ocean floor in summer 2021 and preliminary analyzes show that there is a large amount of registered local seismicity that is not recorded by land seismological stations. We are investigating the effect of this local seismicity on seepage activity and sediment instabilities. Another experiment with seabed seismometers was conducted to study how the local stress affects the transport of horizontal waves through gas structures in the sediment. PhD students and postdocs within the project have participated in many marine expeditions and gained invaluable experience in collecting, processing and interpreting geological and geophysical data. An initial model of the stress generated by the advance and retreat of the Barents Sea icesheet and the current weight of the Greenland icesheet, is now available. This model suggests that the stress regime has been favorable to open up faults and fractures in periods following the major glaciations. This mechanism may explain periodic intensification of the gas release. Numerical simulations of the physical mechanisms that control gas emissions are helping us to understand why methane emissions have stopped along part of the margin. An interplay between the amount of gas in the sediment and the pressure exerted at cracks controls how much and when the gas release occurs. Different geological processes affect the pressure field that controls the seepage. The concepts and approaches developed by SEAMSTRESS for the west-Svalbard margin are proving to be relevant for other regions, e.g., the Barents Sea, where methane seepage is widespread and dominated by complex post-glacial tectonism.