Why are methane levels over the Arctic Ocean high from October to March?

Water temperatures at different depth

Why are methane concentrations in the atmosphere over the Arctic Ocean so high from October through to March?

The image below, replotted by Leonid Yurganov from a study by Chepurin et al, shows sea water temperature at different depths in the Barents Sea.

Above image illustrates that, while Arctic sea water at the surface reaches its highest temperatures in the months from July to September, water at greater depth reaches its highest temperature in the months from October to March. Accordingly, huge amounts of methane are starting to get released from the Arctic Ocean's seafloor in October.

Surface temperatures in October

As the image below shows, temperature at 2 meters was below 0°C (32°F, i.e. the temperature at which water freezes) over most of the Arctic Ocean on October 26, 2014. The Arctic was over 6°F (3.34°C) warmer than average, and at places was up to 20°C (36°F) warmer than average.

  

Image from 'Ocean temperature rise'

At the same time, continents around the Arctic Ocean are frozen. Surface temperatures over the Arctic Ocean were higher than temperatures on land at the end of October, due to the enormous amounts of heat being transferred from the waters of the Arctic Ocean to the atmosphere. This was the result of ocean heat content, which in 2014 was the highest on record, especially in the Arctic Ocean, which also made that at that time of year the sea ice extent was still minimal in extent and especially in volume. 

Start of freezing period

In October, the Arctic Ocean typically freezes over, so less heat will from then on be able to escape to the atmosphere. Sealed off from the atmosphere by sea ice, greater mixing of heat in the water will occur down to the seafloor of the Arctic Ocean.

Less fresh water added to Arctic Ocean

The sea ice also seals the water of the Arctic Ocean off from precipitation, so no more fresh water will be added to the Arctic Ocean due to rain falling or snow melting on the water. In October, temperatures on land around the Arctic Ocean will have fallen below freezing point, so less fresh water will flow from glaciers and rivers into the Arctic Ocean. At that time of year, melting of sea ice has also stopped, so fresh water from melting sea ice is no longer added to the Arctic Ocean either. 

Rising salt content

As addition of fresh water ends, the salt content of the water in the Arctic Ocean starts to rise accordingly, while the Gulf Stream continues to push salty water into the Arctic Ocean. The higher salt content of the water makes it easier for ice to melt at the seafloor of the Arctic Ocean. Saltier water causes ice in cracks and passages in sediments at the seafloor of the Arctic Ocean to melt, allowing methane contained in the sediment to escape. 

Pingos and conduits. Hovland et al. (2006)

The image on the right, from a study by Hovland et al., shows that hydrates can exist at the end of conduits in the sediment, formed when methane did escape from such hydrates in the past. Heat can travel down such conduits relatively fast, warming up the hydrates and destabilizing them in the process, which can result in huge abrupt releases of methane.

Heat can penetrate cracks and conduits in the seafloor, destabilizing methane held in hydrates and in the form of free gas in the sediments.

Less hydroxyl in atmosphere

Besides heat, open water also transfers more moisture to the air. The greater presence of sea ice from October onward acts as a seal, making that less moisture will evaporate from the water. Less moisture evaporating, together with the change of seasons (i.e. less sunshine) results in lower hydroxyl levels in the atmosphere at the higher latitudes of the Northern Hemisphere, in turn resulting in less methane being broken down in the atmosphere over the Arctic.

Gulf Stream

Malcolm Light writes in this and this earlier posts that the volume transport of the Gulf Stream has increased by three times since the 1940's, due to the rising atmospheric pressure difference set up between the polluted, greenhouse gas rich air above North America and the marine Atlantic Air. 

The increasingly heated Gulf Stream with its associated high winds and energy rich weather systems then flows NE to Europe where it is increasingly pummeling Great Britain with catastrophic storms, as also described in this earlier post, which adds that faster winds means more water evaporation, and warmer air holds more water vapor, so this can result in huge rainstorms that can rapidly devastate the integrity of the ice. The image below further illustrates the danger of strong winds over the North Atlantic reaching the Arctic.

Branches of the Gulf Stream then enter the Arctic and disassociate the subsea Arctic methane hydrate seals on subsea and deep high - pressure mantle methane reservoirs below the Eurasian Basin - Laptev Sea transition. This is releasing increasing amounts of methane into the atmosphere where they contribute to anomalously high local temperatures, greater than 20°C above average.

From: The Biggest Story of 2013

Emissions from North America are - due to the Coriolis effect - moving over areas off the North American coast in the path of the Gulf Stream (see animation on the right).

The Gulf Stream reaches its maximum temperatures off the North American coast in July. It can take almost four months for this heat to travel along the Gulf Coast and reach the Arctic Ocean, i.e. water warmed up off Florida in early July may only reach waters beyond Svalbard by the end of October.

Waters close to Svalbard reached temperatures as high as 63.5°F (17.5°C) on September 1, 2014 (green circle). The image below shows sea surface temperatures only - at greater depths (say about 300 m), the Gulf Stream can push even warmer water through the Greenland Sea than temperatures at the sea surface.

Since the passage west of Svalbard is rather shallow, a lot of this very warm water comes to the surface at that spot, resulting in an anomaly of 11.9°C. The high sea surface temperatures west of Svalbard thus show that the Gulf Stream can carry very warm water (warmer than 17°C) at greater depths and is pushing this underneath the sea ice north of Svalbard.

from: Causes of high methane levels over Arctic Ocean 

Through to March the following year, salty and warm water (i.e. warmer than water that is present in the Arctic Ocean) will continue to be carried by the Gulf Stream into the Arctic Ocean, while the sea ice will keep the water sealed off from the atmosphere, so little heat and moisture will be able to be transferred to the atmosphere. 

Start of melting period

This situation continues until March, when the sea ice starts to retreat and more hydroxyl starts getting produced in the atmosphere. Increased sea ice melt and glaciers melt, the latter resulting in warmer water flowing into the Arctic Ocean from rivers, will cause salinity levels in the Arctic Ocean to fall, in turn causing methane levels to fall in the atmosphere over the Arctic Ocean. Furthermore, the water traveling along the Gulf Stream and arriving in the Arctic Ocean in March will be relatively cold.  

References


- Chepurin, G.A., and J.A. Carton, 2012: Sub-arctic and Arctic sea surface temperature and its relation to ocean heat content 1982-2010, J. Geophys. Res.-Oceans., 117, C06019, DOI: 10.1029/2011JC007770. http://onlinelibrary.wiley.com/doi/10.1029/2011JC007770/abstract 

- Combination image created by Sam Carana with Climate Reanalyzer, from: Temperature Rise, http://arctic-news.blogspot.com/2014/10/ocean-temperature-rise.html 

- Submarine pingoes: Indicators of shallow gas hydrates in a pockmark at Nyegga, Norwegian Sea, by Martin Hovland and Henrik Svensen (2006) http://www.sciencedirect.com/science/article/pii/S0025322705003968

- Sea surface temperature west of Svalbard,
created by Sam Carana with
http://earth.nullschool.net

Post by Sam Carana.

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.

More on Wildfires

Previous posts have highlighted the huge amounts of carbon dioxide, methane and soot being emitted as a result of wildfires. Apart from this, there are further important pollutants to consider in regard to their potential to contribute to warming, especially at high latitudes.

The image below, dated August 7, 2013, and kindly supplied by Leonid Yurganov, shows high levels of carbon monoxide as a result of wildfires in Siberia, reaching high up into the Arctic all the way to Greenland. 

[ click on image to enlarge ]

Formation of tropospheric ozone mostly occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs) react in the atmosphere in the presence of sunlight. NOx, CO, and VOCs are therefore called ozone precursors. Apart from a health hazard, tropospheric ozone is an important greenhouse gas. Furthermore, carbon monoxide emissions contribute to hydroxyl depletion, thus extending the lifetime of methane.

While there appears to be little or no carbon dioxide from wildfires over North America on the above August 7 image, there are many recent wildfires raging over the North American continent, as illustrated by the August 12 map below, from Wunderground. 

[ click on image to enlarge ]

This point is illustrated even better on the image below [added later, ed.] showing a composite image with carbon monoxide over July 3-13, 2013. Carbon monoxide resulting from wildfires in Canada is seen crossing the Atlantic Ocean, due to the Coriolis effect, as well as reaching Greenland in large amounts.

[ click on image to enlarge ]

Related

- Wildfires even more damaging
http://arctic-news.blogspot.com/2013/07/wildfires-even-more-damaging.html

- The Threat of Wildfires in the North
http://arctic-news.blogspot.com/2013/06/the-threat-of-wildfires-in-the-north.html

- Wildfires in Canada affect the Arctic
http://arctic-news.blogspot.com/2013/07/wildfires-in-canada-affect-the-arctic.html

Arctic satellite thermal infrared CH4 data compared to surface in-situ and total column measurements

Leonid Yurganov, Senior Research Scientist,
Joint Center for Earth Systems Technology,
University of Maryland Baltimore County

Below an abstract of a paper written by Leonid Yurganov, Xiaozhen Xiong and Ira Liefer, and submitted for presentation at the AGU-Fall meeting 2013.

ABSTRACT: The trace gas sensitivity of Thermal InfraRed (TIR) sounders (AIRS, IASI, TANSO) is greatest in the middle and upper troposphere; though, lower troposphere (1-2 km of altitude) sensitivity is less but not negligible. As a result, where methane largely is constrained to the lower troposphere, as is common in the Arctic particularly the marine Arctic, retrievals from these instruments provides important synoptic data on high latitude methane sources. Low Arctic water vapor content favors a better sensitivity to methane as well: H2O is the main absorber in the 7.8 micrometers spectral region.

Both AIRS/Aqua v6 (NASA) and IASI/Metop-A (NOAA/NESDIS/CLASS retrievals) methane data averaged over 0-4 km altitude clearly demonstrate increased methane concentrations over the Barents and Norwegian Seas (BNS) with seasonal maximum in December - March. Similar increases are observed over the Kara, Laptev, and Chukchi Seas for September-November, i.e. during the period of minimum ice cover over the Arctic (Figures 1 and 2). Comparison of a long series of AIRS data with in situ methane concentrations at the Zeppelin NILU observatory (Svalbard) show good agreement both in amplitude and phase of seasonal variations. Agreement with Barrow NOAA continuous methane in situ data is much worse, which likely results from lower thermal contrast in winter over the cold and icy surfaces of the Eastern Arctic. Further surface validation is by a comparison of total methane columns with the Sun-Tracking FTIR at Ny-Alesund, Svalbard (TCCON network).

These analyses demonstrate that TIR satellites are capable of detecting Arctic methane enhancements from space, particularly over relatively warm year-round water surfaces such as the BNS. Ongoing research is addressing further verification of retrieved methane columns by collecting data with a cavity ring-down spectroscopy analyzer for methane and carbon dioxide on board of the Russian Research Vessel Akademik Fedorov during the expedition NABOS-2013. Data will be collected to measure marine methane concentrations and vertical fluxes between Norway and the Eastern Arctic (New Siberian Islands) between 20 August and 23 September, 2013.

Figure 1

Figure 2. methane concentrations over the Barents and Norwegian Seas (BNS), over the Kara, Laptev, and East Siberian Seas, and over Eurasia (between 50 and 70 degrees North)