Methane, Faults and Sea Ice

Shield breaking down

Until now, Arctic sea ice has been acting as a shield, in a number of ways, including:

• preventing sunlight from warming up water underneath the sea ice 
• facilitating currents that currently cool the bottom of the sea
• preventing much methane from entering the atmosphere; as discussed in an earlier post, the sea ice collects and holds the methane in places close enough to the surface for the methane to be consumed through photochemical and biochemical oxidation. 

However, as the sea ice declines, this shield is breaking down. As a result:

• more sunlight is reaching the water, contributing to warming of water in the Arctic Ocean
• sea ice decline comes with the danger of weakened currents that cool the seabed
• more methane is able to penetrate the cracks and openings in the ever-thinner ice. 

Warm Water traveling along Gulf Stream

At the same time, global warming is causing more extreme weather events to occur, such as the record warmth observed in July 2013 in part of the northeastern Atlantic Ocean off the coast of North America. As discussed in a recent post, this warm water has meanwhile traveled along the Gulf Stream and reached the Arctic Ocean.

Methane venting from Seabed

As a result, warmer water is now destabilizing sediments under the seabed that hold huge amounts of methane in the form of free gas and hydrates. Methane is now venting from the seabed of the Arctic Ocean, driven by sea ice decline and "by Gulf Stream heating, earthquakes and deep pyroclastic eruptions", as Malcolm Light explains in a recent comment and as described in an earlier post.

The image below shows the result: Massive amounts of methane venting from the seabed, penetrating the sea ice, and entering the atmosphere over the Arctic Ocean. 

Methane, Faults and Sea Ice

The animation below illustrates links between: 

• The fault line that crosses the Arctic Ocean and forms the boundery between two tectonic plates (i.e. the North American Plate and the Eurasian Plate)
• Arctic sea ice, which until now has acted as a shield
• The prominence of high methane readings over the Arctic Ocean 

Causes of high methane levels over Arctic Ocean

Methane levels in the atmosphere over the Arctic Ocean are very high, as illustrated by the image below, by Leonid Yurganov, showing IASI methane readings for October 11-20, 2013.

Previous posts have discussed these high levels of methane, pointing at links between high methane levels over Arctic Ocean and earthquakes and volcanic activity.

Malcolm Light points at another factor that is contributing to the high methane levels observed over the Arctic Ocean in October 2013.

Malcolm says: The massive methane release in the Arctic this October is partly because the Gulf Stream waters got massive heating in the Atlantic off the North American coast in July. It takes the Gulf Stream currents almost 4 months to reach the emission sites along the southern side and end of the Eurasian Basin. This combined with the earthquake activity along the Gakkel Ridge and deep pyroclastic eruptions is escalating the rate of methane release by destabilizing the submarine Arctic methane hydrates at increasing rates.

The NOAA image below shows temperature anomalies for July 2013. NOAA adds that in July 2013 many regions were much warmer than average, with part of the northeastern Atlantic off the coast of North America observing record warmth.

The image below shows how water traveling along the Gulf Stream ends up in the Arctic Ocean. Water in the Gulf Stream travels at 4 miles per hour, but slows down to less than 1 mile per hour in the North-Atlantic Current. This means that water warmed up off Florida in July will start reaching waters beyond Svalbard in October.

The image below, from Malcolm Light's September 2012 post Further Confirmation of a Probable Arctic Sea Ice Loss by Late 2015, shows how warm water flows into the Arctic Ocean and warms up methane hydrates and free gas held in sediments under the Arctic Ocean.

 The image below shows the methane readings over the past few days on the Northern Hemisphere.

Warming Gulf Stream causes methane release

The Gulf Stream (dashed lines on NOAA image below) pushes warm water north.

Phrampus & Hornbach (2012) have analyzed the stability of methane hydrates along the Carolina rise off the east coast of North America using active-source seismic reflection data, with the goal of characterizing hydrate stability below the Gulf Stream.

The study suggests that ocean warming above the Carolina rise, caused by a warming Gulf Stream, is rapidly destabilizing methane hydrate along a broad swathe of the North American margin.

The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures.

The image on the right shows the study area; the pink area is where methane hydrate is destabilizing owing to recent changes in ocean temperature; the approximate location of the Gulf stream is between the two solid black arrows.

Over the past 5,000 years or so, the western North Atlantic margin has been warming by up to eight degrees Celsius. This is now triggering the destabilization of an estimated 2.5 gigatonnes of methane hydrate. The analysis suggests that we are observing the onset of methane hydrate destabilization along an ~300-km span of the North American margin that will continue for centuries unless the Gulf Stream shifts southward or intermediate ocean temperatures cool several degrees.

If continuing hydrate destabilization triggers slope failure at this site, the amount of methane released could be an order of magnitude greater. Furthermore, recent studies have suggested that similar ocean temperature shifts are taking place elsewhere, notably in the Arctic Ocean; the estimate of 2.5 gigatonnes of destabilizing methane hydrate is therefore likely to represent only a fraction of the methane hydrate currently destabilizing globally.

Without action, global warming looks set to increase temperature anomalies in the oceans. The above image shows the sea surface temperature anomalies that are now present along the east coast of North America.

In many ways, the situation in the Arctic is even more dire than in the Carolina rise. A warming Gulf Stream will push warmer water into the Arctic, which has many areas with extremely shallow seas, giving methane little opportunity to be oxidized in the sea. Furthermore, colder water in the Arctic is less friendly toward microbes that can decompose methane in the water. Once methane does reach the atmosphere, there's little hydroxyl in the Arctic atmosphere to decompose the methane there.

Most importantly, the Arctic contains huge amounts of methane and the Arctic is experiencing huge temperature anomalies in summer, due to albedo changes and further feedbacks. Therefore, the Arctic looks set to experience huge abrupt releases of methane that will add to make the situation in the Arctic worse, in a vicious spiral threatening to escalate into runaway global warming.

References

- Recent changes to the Gulf Stream causing widespread gas hydrate destabilization, Phrampus & Hornbach, Nature 490, 527–530 (25 October 2012) doi:10.1038/nature11528
http://www.nature.com/nature/journal/v490/n7421/full/nature11528.html

Related

- Big changes in Arctic within years
arctic-news.blogspot.com/2012/10/big-changes-in-arctic-within-years.html

- Diagram of Doom
arctic-news.blogspot.com/2012/08/diagram-of-doom.html

- How extreme will it get?
arctic-news.blogspot.com/2012/07/how-extreme-will-it-get.html

- The potential impact of large abrupt release of methane in the Arctic
arcticmethane.blogspot.com/2012/05/potential-impact-of-large-abrupt.html

- Methane in the Arctic
arctic-news.blogspot.com/2012/05/video-and-poster-methane-in-arctic.html