Trapping heat within the Earth’s atmosphere, greenhouse gases are a driving force behind global warming. Methane is a greenhouse gas that traps more heat than carbon dioxide and can stay in the atmosphere for 12 years. Landfills, coal mining, fossil fuels, and animal agriculture are all major sources of methane emission. However, there is another source of methane emission: the ocean.
Methane gas emission by the ocean is caused by geological processes that happen on or under the seabed, triggered by stress and fractures. How ocean methane emission works is not well understood, but if these emissions reach the atmosphere it could affect the global methane budget. A recent study on the Arctic ocean published in Nature suggests that changes in sea level could affect methane emissions.
“Earth systems are interconnected in ways that we are still deciphering, and our study reveals one of such interconnections in the Arctic: The moon causes tidal forces, the tides generate pressure changes, and bottom currents that in turn shape the seafloor and impact submarine methane emissions. Fascinating!” study co-author Dr Andreia Plaza-Faverola said in a press release.
The study took place on Vestnesa ridge, an extensively studied system of methane seepage on the western Svalbard margin. Svalbard is a Norwegian island group in the Arctic Ocean, located between Norway and the North Pole. Researchers measured pressure and temperature data from two piezometers located 80 kilometers (49.7 miles) apart. Measurements at high and low tide were used to assess how sea level affects gas seepage.
The results of the study showed that tidal change in sea level corresponded with changes in gas release. Dr Faverola explained, “We noticed that gas accumulations, which are in the sediments within a meter from the seafloor, are vulnerable to even slight pressure changes in the water column. Low tide means less of such hydrostatic pressure and higher intensity of methane release. High tide equals high pressure and lower intensity of the release”
This indicates that even small changes in sea level might affect methane gas emission from the seabed. Researchers claim that this means rising sea levels as a result of global warming could in fact reduce methane output from the ocean, but clarify that increased temperature would increase ocean gas output. These two phenomena would counterbalance each other. Also, the likelihood of methane reaching the atmosphere is lower in deeper water.
The authors of the study note that future research will need to be carried out in shallow waters, over a long period. This is due to the possibility of methane reaching the atmosphere is greater in shallow waters versus deep. This would further our understanding of how changes in sea level could affect the release of this greenhouse gas from our oceans.