Full moon in Tromsø, Norway. Credit: Maja Sojtaric
Floods could even counteract the potential threat of the submarine methane release from the warming North Pole.
It may not be very well known, but the Northern Ocean leaks enormous amounts of the powerful greenhouse gas methane. These leaks have been going on for thousands of years, but could be amplified by a future warmer ocean. The potential for this gas to escape from the ocean and contribute to the greenhouse gas budget in the atmosphere is an important mystery that scientists are trying to solve.
The total amount of methane in the atmosphere has increased tremendously in recent decades, and although some of the increase can be attributed to human activity, other sources are not very limited.
A recent paper in Nature communication even implies that the moon must play a role.
Small pressure changes affect methane emissions
The moon controls one of the most formidable forces in nature – the tides that form our coastlines. Tides in turn significantly affect the intensity of methane releases from the seabed of the Arctic Ocean.
‘We have noticed that gas accumulations, within a meter of the seabed in the sediments, are vulnerable to even slight pressure changes in the water column. Low tide means less of such hydrostatic pressure and a higher intensity of methane release. High water equals high pressure and lower intensity of release, says co-author of the newspaper Andreia Plaza Faverola.
‘This is the first time this observation has been made in the Arctic Ocean. This means that slight pressure changes can release significant amounts of methane. This is a game changer and the biggest impact of the study. Says another co-author, Jochen Knies.
New methods reveal unknown release sites
Plaza Faverola points out that the observations were made by placing a tool called a piezometer in the sediments and leaving it there for four days.
Remove the pressure instrument, piezometer, which monitors the release of methane from the ocean floor sediments. Photo: Screenshot of video. Credit: Przemyslaw Domel
It measured the pressure and temperature of the water in the bubbles of the sediment. Hourly changes in the measured pressure and temperature have revealed the presence of gas near the seabed rising and falling as the tides change. The measurements were made in an area of the Northern Ocean where no methane release was previously observed, but where massive gas hydrate concentrations were sampled.
‘It tells us that the release of gas from the seabed is more widespread than we can see with traditional sonar recordings. We saw no bubbles or columns of gas in the water. Gas bursts with a period of several hours will not be identified unless a permanent monitoring tool is available, such as the piezometer. ‘Sê Plaza Faverola
Methane emissions can be seen as torches rising from the seabed. But the release is not always visible using the usual methods. Screenshot of data visualization by Andreia Plaza Faverola. Credit: Andreia Plaza Faverola
These observations imply that the quantification of current gas emissions in the Arctic can be underestimated. However, high tide seems to affect gas emissions by reducing its length and volume.
“What we found was unexpected and the implications are huge. This is a deep water site. Small pressure changes can increase the gas release, but the methane will still remain in the sea due to the water depth. But what is happening in shallower areas? This approach must also be done over a longer period of time in shallow North Pole waters. In shallow water, methane is more likely to reach the atmosphere. Says Knies.
Can counteract the temperature effects
Thus, high sea levels appear to affect gas release by possibly reducing their altitude and volume. The question remains whether sea level rise due to global warming can partially balance the effect of temperature on submarine methane emissions.
‘Earth systems are interconnected in a way we still decipher, and our study reveals one such interconnection in the North Pole: the moon causes tidal forces, the tides generate pressure changes and bottom currents which in turn form the seabed and the underwater methane affects emissions. Fascinating! Says Andreia Plaza Faverola.
Reference: “Impact of tides and sea level on the deep-sea Arctic methane release” by Nabil Sultan, Andreia Plaza-Faverola, Sunil Vadakkepuliyambatta, Stefan Buenz and Jochen Knies, 9 October 2020, Nature communication.
DOI: 10.1038 / s41467-020-18899-3
The paper is the result of a collaboration between CAGE and Ifremer under the project SEAMSTRESS – Tectonic stress effects on Arctic methane seepage