https://jdigitaldiagnostics.com/0869-7698/article/view/676028
This caused the lasting contact of relatively warm bottom waters (~(–1) °C) and frozen sediments (~(–25) °C) of the Arctic shelf for 5–6 thousand years longer than in previous warm geological epochs, which led to the progressive degradation of subsea permafrost, formation of deep or through taliks (zones of melted permafrost) and destabilization of Arctic shallow hydrates. It is shown that the increasing runoff of Siberian rivers, mobilization, transport, and transformation of terrestrial organic matter in the Arctic land–shelf system determines the sedimentation and biogeochemistry of the East Siberian Arctic Shelf – the broadest and shallowest shelf in the World Ocean, which makes up more than 70% of the Northern Sea Route area.
https://jdigitaldiagnostics.com/0869-7698/rt/metadata/676028/191363
For hundreds of millions of years, only a small part of incoming solar radiation (0.06%) was used in the process of photosynthesis, which became the basis of life on Earth and its product - fossil fuels. Until recently, humanity developed due to its use and did not realize that reserves of natural fuel were depleted at a rate 100 thousand times greater than they were formed. The earliest evidence of the use of energy from burned fuel to heat caves inhabited by our ancestors in the territory of today's China dates back to 400 thousand years BC.
During interglacial periods, the average air temperature was 6–7 °C higher than during glacial periods. The greatest amplitudes of climate fluctuations were documented in the Arctic, where warming during warm geological periods reached 10–12 °C, i.e. approximately 2 times higher than the global average [ 1–6 ]. This phenomenon was called arctic amplification [ 7 ] .
The radiative activity of methane is 20-35 times higher, and the rate of increase in concentration is approximately 2-4 times higher than that of CO 2 [ 8 , 9 ]. The contribution of the increase in the content of atmospheric CH 4 to the greenhouse effect is estimated at approximately 30% of the contribution of CO 2 . However, there are experimental and model estimates indicating that for a 20-year range, the molecule-to-molecule radiative efficiency of CH 4 exceeds that of CO 2 by 84 times.
Since 2007, an increase in the rate of atmospheric methane growth has been recorded at high latitudes of the Northern Hemisphere, which has led to the accumulation of additional amounts of CH 4 of unknown genesis in the atmosphere [ 26 ]. A possible additional source of CH 4 entering the atmosphere at high latitudes of the Northern Hemisphere is atmospheric CH 4 emissions due to the degradation of terrestrial and submarine permafrost on the Arctic Ocean shelf, where organic matter has accumulated in quantities much greater than the atmospheric pool of major greenhouse gases [ 17–21 , 23 ]. The authors of this paper proposed 30 years ago a hypothesis about the increasing role of submarine permafrost degradation and destabilization of giant reserves of Arctic shelf methane hydrates as the main natural source of CH 4 at high latitudes of the Northern Hemisphere, in addition to CH 4 emissions from northern thermokarst lakes [ 17 , 21 , 27–32 ].
This is the so-called methane catastrophe – the release of large amounts of methane from gas hydrates located in the depths of the Earth [ 38–40 ]. The most realistic cause of rapid climate change was named as the destabilization of shallow Arctic shelf hydrates. However, before the start of comprehensive studies of the MVA by the authors' team in the late 1990s–early 2000s, which proved the progressive degradation of the MVA underwater permafrost and massive emissions of CH 4 from bottom sediments into the water column–atmosphere [ 17 , 20 , 21 , 31 ], it was generally accepted that there was no climate hazard from the so-called methane bomb , at least for the next hundreds of years – due to the quasi-stable state of the underwater permafrost–hydrate system [ 8 , 9 , 39 ].
Moreover, the “most representative” models of climate evolution summarized in [ 8 , 9 , 14 ] and based on the assumption that by the end of the 21st century the CO 2 content in the atmosphere will double due to anthropogenic activity, do not take into account the possible increase in the CH 4 content , the contribution of which to the greenhouse effect may become comparable and even more significant (due to the degradation of marine underwater permafrost and gas hydrates, increased development of subaerial and underwater thermokarst, evolution of lakes and sublake/channel taliks) than the contribution of anthropogenic CO 2 , provided that global warming continues to occur in the near future [ 9–11 , 14 ].
The uniqueness of the MVA is that it is the shallowest and widest shelf of the World Ocean, where giant reserves of hydrates have accumulated, the destabilization of which leads to massive bubble discharge from bottom sediments into the water column-atmosphere. Unlike the deep ocean, a significant portion of the bubble methane reaches the atmosphere, which leads to the formation of increased concentrations of atmospheric methane. Therefore, the MVA, where more than 80% of underwater permafrost and giant reserves of hydrates are located, is considered the only region of the World Ocean that can play an important climatic role [ 18 , 19 , 38–40 ].
A conservative estimate of the emission from the shallow part of the MVA into the atmosphere is approximately 17 Tg [ 53 ], which is approximately 3 times higher than the estimate for the World Ocean. However, taking into account more recent estimates [ 56 ], this value will be revised in the near future towards a significant increase. This means that even when considering the minimum estimates, the MVA shelf can be considered as the main modern marine source of CH 4 entering the atmosphere. This estimate includes all processes: the entry of CH 4 from bottom sources, as well as microbial formation and oxidation in sediments and the water column. If we return to the presence of an atmospheric maximum of CH 4 over the Arctic (Fig. 3), it becomes obvious that the source under study plays a more important role compared to the anthropogenic source, which is concentrated in the temperate latitudes of the Northern Hemisphere.
Compared to stable continuous terrestrial permafrost, the temperature of which has not yet risen above –11 °C, submarine permafrost is in transit – close to the phase transition [ 53 , 57 ]. When the permafrost integrity is disrupted, free gas from the destroyed gas hydrates enters the water column and then into the atmosphere [ 17 , 21 ]. It has been shown that the MVA is a unique region, since >80% of the inferred submarine permafrost and shallow-water Arctic gas hydrates are located in the MVA (Fig. 16).
Considering that the MVA shelf contains approximately 1750 Gt of carbon in the form of gas hydrates (750 Gt), natural gas (500 Gt) and permafrost OM (500 Gt), and the modern atmosphere contains approximately 750 Gt of C-CO2 and 4 Gt of C-CH4 [ 8 , 9 , 17–21 ] , it becomes obvious that the involvement of carbon from underwater permafrost in the cycle, even in small fractions of a percent of the total volume of the permafrost carbon reservoir, can lead to a significant increase in the total content of CH4 in the atmosphere [ 17 , 21 ]. Assuming that hydrates are already destabilized beneath the through taliks and considering that the area of through taliks on the MVA shelf is 5–10% [ 49 ], the potential emission into the atmosphere may be from 37.5 to 75 Gt, which, under different scenarios of atmospheric emission kinetics [ 105 ], may cause climate warming at least comparable to the effect of the expected doubling of atmospheric CO 2 content by the end of 2100 [ 9 ].
up to US$60 trillion (extreme scenario) in the case of the emission of approximately 50 Gt of methane over 10 years, which will lead to additional warming of the climate by approximately 2 °C 15–35 years after such a massive emission [ 108 ].However, fundamental research on the project topic continues within the framework of joint publications with strategic partners from Sweden (the group of Professor Orjan Gustafson of Stockholm University, Academician of the Royal Swedish Academy of Sciences, Member of the Nobel Council in Chemistry), Italy (Professor Tommaso Tesi from the University of Bologna) and the USA (Professor Janek Martens, Lamont Doherty Observatory),
About the authors
Igor P. Semiletov
VI Il'ichev Pacific Oceanological Institute, FEB RAS; Sakhalin State University/SakhTECHAuthor for correspondence.
Email: ipsemiletov@gmail.com
ORCID iD: 0000-0003-1741-6734
Corresponding Member of RAS, Doctor of Sciences in Geography, International Center of the Far-Eastern and Arctic Seas (named by admiral S.O. Makarov)
Russian Federation, Vladivostok; Yuzhno-SakhalinskNatalia E. Shakhova
V. I. Il’ichev Pacific Oceanological Institute, FEB RAS; M. A. Sadovskу Institute of Geosphere DynamicsEmail: nataliaeshakhova@gmail.com
Doctor of Sciences in Geology and Mineralogy
Russian Federation, Vladivostok; Moscow
No comments:
Post a Comment