Klimat

*Vast methane plumes escaping from the seafloor* discovered in Siberian Arctic Sea

20 kwietnia 2015
min
(galeria fotografii)

Na syberyjskim morzu arktycznym odkryto "olbrzymie wycieki metanu z dna morsiego” (po angielsku; Daily Kos) 

Methane megaflare on Laptev Sea slope at around 62m depth.
attribution: http://polar.se/en/blogg/mega-flare/
Methane megaflare on Laptev Sea slope at around 62m depth. "We are “sniffing” methane. We see the bubbles on video from the camera mounted on the CTD or the Multicorer. All analysis tells the signs. We are in a Mega flare. We see it in the water column we read it above the surface an we follow it up high into the sky with radars and lasers. We see it mixed in the air and carried away with the winds. Methane in the air." Ulf Hedman, Science Coordinator, Swedish Polar Research Secretariat
Vast methane plumes have been discovered boiling up from the seafloor of the Arctic ocean on the continental slope of the Laptev Sea by a dream team of international scientists. Over the last decade a warming tongue of Atlantic ocean water has been flowing along the Siberian Arctic ocean's continental slope destabilizing methane ice, hypothesize the team of Swedish, Russian and American scientists. The research team will take a series of measurements across the Siberian seas to attempt to understand and quantify the methane release and predict the effect of this powerful greenhouse gas on global and Arctic warming. Because the Siberian Arctic contains vast stores of methane ices and organic carbon that may be perturbed by the warming waters and Arctic climate, Arctic ocean and Siberian sea methane release could accelerate and intensify Arctic and global warming.
SWERUS expedition plan map
SWERUS expedition preliminary cruise plan and study areas of Leg 1 and 2. EEZ=Exclusive Economic Zone; LR=Lomonosov Ridge; MR=Mendeleev Ridge; HC=Herald Canyon; NSI=New Siberian Islands.
Örjan Gustafsson's blog post of this discovery gave me the chills.
So, what have we found in the first couple of days of methane-focused studies?

1) Our first observations of elevated methane levels, about ten times higher than in background seawater, were documented already as we climbed up the steep continental slope at stations in 500 and 250 m depth. This was somewhat of a surprise. While there has been much speculation of the vulnerability of regular marine hydrates (frozen methane formed due to high p and low T) along the Arctic rim, very few actual observations of methane releases due to collapsing Arctic upper slope marine hydrates have been made.  ¨

It has recently been documented that a tongue of relatively varm Atlantic water, with a core at depths of 200–600 m may have warmed up some in recent years. As this Atlantic water, the last remnants of the Gulf Stream, propagates eastward along the upper slope of  the East Siberian margin, our SWERUS-C3 program is hypothesizing that this heating may lead to destabilization of upper portion of the slope methane hydrates. This may be what we now for the first time are observing.

2) Using the mid-water sonar, we mapped out an area of several kilometers where bubbles were filling the water column from depths of 200 to 500 m. During the preceding 48 h we have performed station work in two areas on the shallow shelf with depths of 60-70m where we discovered over 100 new methane seep sites. SWERUS-C3 researchers have on earlier expeditions documented extensive venting of methane from the subsea system to the atmosphere over the East Siberian Arctic Shelf. On this Oden expedition we have gathered a strong team to assess these methane releases in greater detail than ever before to substantially improve our collective understanding of the methane sources and the functioning of the system. This is information that is crucial if we are to be able to provide scientific estimations of how these methane releases may develop in the future.

Here is the SWERUS press release on this discovery.
Methane bubbles discovered on Laptev slope Arctic ocean.
Methane bubbles discovered on Laptev continental slope of Arctic ocean
Just a week into the sampling program and SWERUS-C3 scientists have discovered vast methane plumes escaping from the seafloor of the Laptev continental slope. These early glimpses of what may be in store for a warming Arctic Ocean could help scientists project the future releases of the strong greenhouse gas methane from the Arctic Ocean.

”This was somewhat of a surprise,” writes chief scientist Örjan Gustafsson, Stockholm University, in his latest blog entry. He speculates that the leaking methane from the seafloor of the continental slope may have its origins in collapsing “methane hydrates,” clusters of methane trapped in frozen water due to high pressure and low temperature.

The discovery was made while the icebreaker Oden crosscut the Laptev Sea along a depth gradient from 1000m to just 100m following the continental slope upward to reach the shallow waters of the outer Laptev Sea Shelf. By use of acoustic techniques and geochemical analyses of water samples, the scientists found vast methane plumes escaping from the seafloor at depths between 500 m and 150 m. At several places, the methane “bubbles“ even rose to the ocean surface. What’s more, results of preliminary analyses of seawater samples pointed towards levels of dissolved methane 10–50 times higher than background levels.

“While there has been much speculation about the vulnerability of regular marine hydrates along the continental slopes of the Arctic rim, very few actual observations of methane releases due to collapsing marine hydrates on the Arctic slope have been made,” writes Örjan Gustafsson.

Örjan Gustafsson thinks that the mechanism behind the presence of methane seeps at these depths may have something to do with the ”tongue” of relatively warm Atlantic water, presumably intruding across the Arctic Ocean at 200–600 m depths.” Some evidence have shown that this water mass has recently become warmer. As this warm Atlantic water, the last remnants of the Gulf Stream, propagates eastward along the upper slope of the East Siberian margin, it may lead to destabilization of methane hydrates on the upper portion of the slope. This may be what we are now seeing for the first time,” writes Örjan Gustafsson.

SWERUS-C3 scientists could determine the depth from which methane plumes were bubbling up with the help of precise sonar instruments commonly used to map the bottom of the deep ocean and detect gas seeps in the water column. ”We mapped out an area of several kilometers where bubbles were filling the water column at depths of 200 to 500 m,” writes Örjan Gustafsson. Additional observations include the discovery of over 100 new methane seep sites in the shallower waters of the Laptev shelf (at 60–70m depth), a likely consequence of the thawing subsea permafrost.

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