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Full moon in Tromsø, Norway. Credit: Maja Sojtaric
High tides can even counter the potential threat of submarine methane releases from a warming Arctic.
It may not be very well known, but the Arctic Ocean releases huge amounts of methane, a powerful greenhouse gas. These leaks have been going on for thousands of years but could be intensified by a future warmer ocean. The potential of this gas to escape from the ocean and contribute to the balance of greenhouse gases in the atmosphere is a major mystery that scientists are trying to solve.
The total amount of methane in the atmosphere has increased dramatically over the past decades, and while some of the increase can be attributed to human activity, other sources are not very well limited.
A recent article in Nature communications even implies that the moon has a role to play.
Small pressure changes affect the release of methane
The moon controls one of nature’s most formidable forces – the tides that shape our coasts. The tides, in turn, significantly affect the intensity of methane emissions from the seabed of the Arctic Ocean.
“We have noticed that gas accumulations, which are found in sediments less than one meter from the seabed, are vulnerable to slight variations in pressure in the water column. Low tide means less of such hydrostatic pressure and a higher intensity of methane release. High tide equates to high pressure and lower intensity of the release, ”says article co-author Andreia Plaza Faverola.
“This is the first time that this observation has been made in the Arctic Ocean. This means that slight changes in pressure can release significant amounts of methane. This is a game-changer and the most important impact of the study. Says another co-author, Jochen Knies.
New methods reveal unknown publishing sites
Plaza Faverola points out that the observations were made by placing a tool called a piezometer in the sediment and leaving it there for four days.
Recovery of the pressure tool, the piezometer, which monitored the release of methane from ocean floor sediments. Photo: Screenshot of the video. Credit: Przemyslaw Domel
He measured the pressure and temperature of the water inside the pores of the sediment. Hourly changes in measured pressure and temperature revealed the presence of gas near the seabed that rises and falls as the tides change. The measurements were carried out in an area of the Arctic Ocean where no methane releases were previously observed but where massive concentrations of gas hydrates were sampled.
“This tells us that gas releases from the seabed are more prevalent than what we can see with traditional sonar surveys. We did not see any bubbles or columns of gas in the water. Gas burps that have a periodicity of several hours will not be identified unless a permanent monitoring tool is in place, such as the piezometer. Says Plaza Faverola
Methane releases can be thought of as flares rising from the ocean floor. But the output is not always visible using the usual methods. Screenshot of the data visualization by Andreia Plaza Faverola. Credit: Andreia Plaza Faverola
These observations imply that the quantification of current gas emissions in the Arctic may be underestimated. However, high tides seem to influence gas emissions by reducing their height and volume.
“What we found was unexpected and the implications are significant. It is a deep water site. Small changes in pressure can increase gas emissions, but methane will always stay in the ocean due to the depth of the water. But what happens in the shallower sites? This approach should also be applied in shallow arctic waters over a longer period. In shallow water, the possibility of methane reaching the atmosphere is greater. Knies said.
May counteract the effects of temperature
The high sea level thus seems to influence gas emissions by potentially reducing their height and volume. It remains to be seen whether rising sea levels due to global warming could partially offset the effect of temperature on submarine methane emissions.
“Earth systems are interconnected in ways that we are still deciphering, and our study reveals one of these interconnections in the Arctic: the moon causes tidal forces, the tides generate pressure changes and bottom currents which in turn shape the seabed and impact underwater methane. emissions. Fascinating! ”Says Andreia Plaza Faverola.
Reference: “Impact of Tides and Sea Level on Arctic Methane Emissions in Deep Water” by Nabil Sultan, Andreia Plaza-Faverola, Sunil Vadakkepuliyambatta, Stefan Buenz and Jochen Knies, October 9, 2020, Nature communications.
DOI: 10.1038 / s41467-020-18899-3
This article is the result of a collaboration between CAGE and Ifremer as part of the SEAMSTRESS project – Tectonic Stress Effects on Arctic Methane Seepage
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