High tides may even counter the potential threat of underwater methane emissions from the warming Arctic.
It may not be very well known, but the Arctic Ocean is leaking huge amounts of powerful greenhouse gas methane. These leaks have been going on for thousands of years, but could be exacerbated by a warmer ocean in the future. The potential for this gas to escape from the ocean and contribute to the budget of greenhouse gases 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 part of the increase can be attributed to human activity, other sources are not very well limited.
Recent article in Nature Communications it even suggests that the moon has a role.
Small changes in pressure affect the release of methane
The moon controls one of the most formidable forces in nature – the tides that shape our shores. The tides, in turn, significantly affect the intensity of methane emissions from the seabed of the Arctic Ocean.
“We have noticed that the gas accumulations that are in the sediments within a meter of the seabed are vulnerable to even minor changes in the pressure in the water column. Outflow means less than such hydrostatic pressure and higher intensity of methane release. The tide is equal to high pressure and lower intensity of release “, says the co-author of the article Andreia Plaza Faverola.
“This observation is the first time in the Arctic Ocean. This means that slight changes in pressure can release significant amounts of methane. This is a change in the game and the biggest impact of the study. “Says another co – author, Jochen Knies.
New methods reveal unknown launch sites
Plaza Faverola points out that the observations were made by placing an instrument called a piezometer in the sludge and leaving it there for four days.
It measures the pressure and temperature of the water inside the pores of the sludge. Hourly changes in the measured pressure and temperature revealed the presence of gas near the seabed, which rises and falls when the tides change. The measurements were made in an area of the Arctic Ocean where no methane emissions had previously been observed, but where massive gas hydrate concentrations were sampled.
“This tells us that the release of gas from the seabed is more widespread than we can see using traditional sonar research. We did not see any bubbles or gas columns in the water. Gas bulges that have a periodicity of several hours will not be identified unless there is a permanent monitoring tool, such as a piezometer. “Says Plaza Faverola
These observations suggest that quantifying today’s Arctic gas emissions may be underestimated. However, tides appear to affect gas emissions by reducing their height and volume.
“What we found was unexpected and the consequences are great. This is a deep-sea object. Small changes in pressure can increase gas emissions, but methane will still remain in the ocean due to the depth of the water. But what happens in shallower sites? This approach should also be done in shallow Arctic waters for a longer period. In shallow water, the possibility of methane reaching the atmosphere is greater. “Says Nice.
May counteract temperature effects
Thus, high sea levels appear to affect gas emissions, potentially reducing their height and volume. The question remains whether rising sea levels due to global warming may partially offset the effect of temperature on underwater methane emissions.
“Earth’s systems are interconnected in ways we are still deciphering, and our study reveals one of these interconnections in the Arctic: The moon causes tidal forces, tides generate changes in pressure and bottom currents, which in turn shape the seabed and affect the seabed. underwater methane emissions. Charming! “Says Andrea Plaza Faverola.
Reference: “Impact of Tides and Sea Levels on Deep Arctic Methane Emissions” by Nabil Sultan, Andreia Plaza-Faverola, Sunil Vadakkepuliyambatta, Stefan Buenz and Jochen Knies, 9 October 2020, Nature Communications.
DOI: 10.1038 / s41467-020-18899-3
The document is the result of a collaboration between CAGE and Ifremer on the SEAMSTRESS project – Tectonic stress effects on Arctic methane seepage