I decided to expand the post that I recently made in the Feedbacks thread in the Arctic folder to discuss possible methane emissions from the Arctic seafloor as a possible positive feedback mechanism that could conceivably drive the mean global surface temperature over 9 C in the next century.
In a two-part study by scientists from the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Los Alamos National Laboratory utilized a scenario based on a combination of two computer models of how climate change could impact the millions of tons of methane frozen in sediment beneath the Arctic Ocean. In the initial phase of the project they found that buried deposits of methane hydrates, will decompose as the global temperature increases and the oceans warm. In the second phase, the scientists found that methane would then seep into the Arctic Ocean and gradually overwhelm the marine environment’s ability to break down the gas. Supplies of oxygen, nutrients, and trace metals required by methane-eating microbes would dwindle year-by-year as more methane enters the water. After three decades of methane release, much of the methane may bubble to the surface, where it has the potential to accelerate climate change. The author's (Elliot et al. 2011) conclusions include:
"The vast Arctic shelf supports massive hydrate reservoirs, and many are close to the edge of stability [Archer, 2007]. Since these deposits are often located in the depth range of recently ventilated North Atlantic water masses, relatively small increases in temperature due to climate change may result in dissociation [Lamarque, 2008]. In the present study, methane flow from warming clathrates is calculated by porous-media simulation [Reagan and Moridis, 2008]."
Archer, D. (2007), "Methane hydrate stability and anthropogenic climate change", Biogeosciences, 4, 521-544, doi: 10.5194bg-4-521-2007.
Elliott, S., Maltrud, M., Reagan, M., Moridis, G., and Cameron-Smith, P., "Marine methane cycle simulations for the period of early global warming", Journal of Geophysical Research, Vol. 116, G01010, doi: 10.1029/2010JG00 1300, 2011.
Lamarque, J.F. (2008), "Estimating the potential for methane clathrate instability in the 1% CO2 IPCC AR-4 simulations", Geophys. Res. Lett., 35, L19806, doi: 10.1029/2008GL035291.
Reagan, M.T. (PI), (2011), Interrelation of Global Climate and the Response of Oceanic Hydrate Accumulations, Lawrence Berkeley Laboratory: Task Report 10-1, January 31, 2011.
Reagan, M.T., and Moridis, G.J. (2008), "Dynamic response of oceanic hydrate deposits to ocean temperature change", J. Geophys. Res., 113, 107, 486-513, doi: 10.1029/2008JC004938.
The first attached image from Elliott et al 2011 shows a projection from an Earth Systems Model run at Lawrence Berkeley Labs of the change in Arctic Sea Floor temperatures between 2000 and 2100 for SRES A1B, indicating substantial warming particularly in the East Siberian Arctic Shelf, ESAS.
The second attached image indicates how under conditions with a high positive Arctic Oscillation (AO) index (which is positive about ½ the time), the Arctic Ocean circulation patterns transport relatively warm Atlantic Ocean water directly to the ESAS, thus promoting the degradation of the underwater permafrost in this area, contributing to the accelerated emission of methane from the seafloor.
The third attached image indicates that when the Atlantic Maximum Meridional Overturning anomaly increases around 2030 the Ocean Heat Transport into the Arctic Ocean will more than double from current values (which will provide heat to the Arctic seafloor to degrade relict submerged permafrost and then submerged methane hydrates, starting sometime between 2030 and 2050).
With these three images as background, the following linked reference addresses both the current, and future, situation in the West Yamal continental shelf with regards to degradation of the local subsea permafrost (and these findings will be relevant to the ESAS within two to three decades). The Portnov et al 2014 paper shows that in the West Yamal shelf area the relict subsea permafrost (which traps methane gas beneath it and also stabilizes methane hydrates beneath it) are already degrading to the point of leaking methane gas in the 20 to 50 meter water depth range, and the reference notes that model projections indicates that in the next few decades the ocean water temperature at the seafloor in this area should increase from about 0.5 C to about 2.5 C, which should result in a rapid acceleration of the degradation of this relic subsea permafrost. If indeed, the relict subsea permafrost in the Russian Arctic shelves degrade rapidly due to the introduction of warm ocean currents along the seafloor from the North Atlantic Current, within the next few decades then the world could experience a very large positive feedback, first from the associated release of free methane gas from beneath the previously impermeable permafrost and second from the destabilization of the methane hydrates that were kept in a quasi-stable condition since the last ice age due to the melting of the degrading permafrost keeping the hydrates in a transient low temperature condition.
Portnov, A., J. Mienert, and P. Serov (2014), Modeling the evolution of climate-sensitive Arctic subsea permafrost in regions of extensive gas expulsion at the West Yamal shelf, J. Geophys. Res. Biogeosci., 119, 2082–2094, doi:10.1002/2014JG002685.
http://onlinelibrary.wiley.com/doi/10.1002/2014JG002685/abstractAbstract: "Thawing subsea permafrost controls methane release from the Russian Arctic shelf having a considerable impact on the climate-sensitive Arctic environment. Expulsions of methane from shallow Russian Arctic shelf areas may continue to rise in response to intense degradation of relict subsea permafrost. Here we show modeling of the permafrost evolution from the Late Pleistocene to present time at the West Yamal shelf. Modeling results suggest a highly dynamic permafrost system that directly responds to even minor variations of lower and upper boundary conditions, e.g., geothermal heat flux from below and/or bottom water temperature changes from above permafrost. Scenarios of permafrost evolution show a potentially nearest landward modern extent of the permafrost at the West Yamal shelf limited by ~17 m isobaths, whereas its farthest seaward extent coincides with ~100 m isobaths. The model also predicts seaward tapering of relict permafrost with a maximal thickness of 275–390 m near the shoreline. Previous field observations detected extensive emissions of free gas into the water column at the transition zone between today's shallow water permafrost (<20 m) and deeper water nonpermafrost areas (>20 m). The model adapts well to corresponding heat flux and ocean temperature data, providing crucial information about the modern permafrost conditions. It shows current locations of upper and lower permafrost boundaries and evidences for possible release of methane from the seabed to the hydrosphere in a warming Arctic."
Also see:
http://phys.org/news/2014-12-methane-leaking-permafrost-offshore-siberia.htmlExtract: "Portnov used mathematical models to map the evolution of the permafrost, and thus calculate its degradation since the end of the last ice age. The evolution of permafrost gives indication to what may happen to it in the future.
If the bottom ocean temperature is 0,5°C, the maximal possible permafrost thickness would likely take 9000 years to thaw. But if this temperature increases, the process would go much faster, because the thawing also happens from the top down.
"If the temperature of the oceans increases by two degrees as suggested by some reports, it will accelerate the thawing to the extreme. A warming climate could lead to an explosive gas release from the shallow areas."
Permafrost keeps the free methane gas in the sediments. But it also stabilizes gas hydrates, ice-like structures that usually need high pressure and low temperature to form.
"Gas hydrates normally form in water depths over 300 meters, because they depend on high pressure. But under permafrost the gas hydrate may stay stable even where the pressure is not that high, because of the constantly low temperatures."
Gas hydrates contain huge amount of methane gas, and it is destabilization of these that is believed to have caused the craters on the Yamal Peninsula."
On a related matter, the linked article reported (see the following quote) on the findings from cores that indicated two carbon pulses during the PETM, with the first one smaller than the second; which raises the possibility the with strong forcing, positive feedback mechanisms (particularly from methane hydrates) may be stronger than previously thought:
http://www.nbcnews.com/science/environment/earths-future-ancient-warming-gives-ominous-peek-climate-change-n268721Quote: "Intriguingly, Bowen and his colleagues determined that there were actually two releases of carbon into the atmosphere, one before the PETM and one shortly after it started.
And that may be a sign of scary things to come.
"One possible explanation is that the first, the smaller one, caused some climate change that triggered a second one," Bowen said. "So it's possible that the current pulse we are adding to the atmosphere may trigger unanticipated feedbacks that might lead to warming that could last hundreds of thousands of years."
That first release of carbon could have been the result of volcanism, Bowen says. And that might have caused the oceans to warm, which could have led to the melting of methane that lies in frozen deposits on the sea floor. And that could have accounted for the second pulse.
"We don't need a ton of warming for that to happen," Bowen said. "That's a little scary.""
http://www.nature.com/articles/ngeo2316.epdf?referrer_access_token=8qL2xHzOIEYqtOXeHGWNHNRgN0jAjWel9jnR3ZoTv0MFms2cyCBGVzLm4qXkc0yPPRqtmlhoybdEeLtzJY_dafXV2xa9tGePtpL1D8YTJOU%3D
