Seismogenic-Triggering Mechanism of Gas Emission Activizations on the Arctic Shelf and Associated Phases of Abrupt Warming
Round 1
Reviewer 1 Report
This paper propose new and interesting hypothesis to connect tectonic events and climate changes. There are no enough data to say that this is correct paper. But this paper can give a start for international discussion. Somebody will say – no any connection, somebody will say – yes, there is a connection. I recommend to publish this paper.
Author Response
Thank you for evaluation of this research
Reviewer 2 Report
The author suggests a new concept of warming in the Arctic starting in 1920 and 1980 and lasting for about 20 years, an alternative natural mechanism of seismogenic origin.
The hypothesis suggested by L.Lobkovsky is rather a bold proposal aimed to start a discussion on alternative or additional mechanisms of climate change, specifically in the Arctic. This interesting but too a schematic presentation of the idea causes lots of questions and comments.
Figure 1 presents air temperature curves for the Arctic with two periods of abrupt climate warming. Looks like it is only a specific feature of the Arctic, but to prove it, the author should add analogue curves for other regions of the World. Only then one can look for additional mechanisms of warming acting in the Arctic only.
Figure 4 shows tectonic disturbance propagation towards the Arctic. The author assumes distant propagation of perturbations with velocities of the order of 100 km/year. First, the arrow in this Figure points from Aleutian arc to the Laptev sea. This is not the area where permafrost and meta-stable gas hydrates are widely discussed in the literature (and the author does not suggest any references to prove it). The problem is discussed for the Kara Sea and the north of West Siberia where permafrost bears both gas and gas hydrates and where modeling of the related processes is ongoing.
In terms of impact on climate warming velocities of 100 km/year mean that the closer to the Aleutian seismic zone, the earlier will warming start shifting every year 100 km north-west! Such a phase shift should be then clearly seen in the air temperature records from respective weather stations, which are sparse but exist between Aleutian arc and Kara sea region where gas-saturated permafrost is located.
Methane release from permafrost due to stress is a good question to be discussed. The author suggests a model of permafrost consisting of a matrix and pores containing gas-saturated ice and hydrates inclusions (Fig. 5). This model is very far from the real structure of permafrost responding to stress. The matrix as follows from the scheme is considered a continuum with closed pores, but this is not the case. Particles are surrounded by adsorbed water films, pores containing not only ice and gas but also unfrozen water amount of which strongly depends on the concentration of salts. Saline sediments are exactly the case of permafrost saturated with gas. The scheme in Fig. 5 is not applicable in the case of permafrost.
Lines 147-148: “When the pressure in the inclusion-surrounding matrix decreases, a high pressure gradient arises at the boundaries of the inclusions…” Why pressure in the matrix decreases?
Lines 151-153: “destruction of the inclusions’ superficial zone, creating a boundary layer with elevated permeability within the inclusions ...Through this layer, gas flows from the inclusions into the permeable matrix” Why matrix is permeable? Permafrost is rather considered impermeable for water for sure, and gas – most likely.
References are not up to date. So many new data were obtained and laboratory experiments performed on the topic of permafrost and gas hydrates which are not mentioned in the paper. If it was limited to climate change to be caused by seismic events, it probably would cause fewer comments.
Author Response
The author suggests a new concept of warming in the Arctic starting in 1920 and 1980 and lasting for about 20 years, an alternative natural mechanism of seismogenic origin.
The hypothesis suggested by L.Lobkovsky is rather a bold proposal aimed to start a discussion on alternative or additional mechanisms of climate change, specifically in the Arctic. This interesting but too a schematic presentation of the idea causes lots of questions and comments.
- Figure 1 presents air temperature curves for the Arctic with two periods of abrupt climate warming. Looks like it is only a specific feature of the Arctic, but to prove it, the author should add analogue curves for other regions of the World. Only then one can look for additional mechanisms of warming acting in the Arctic only.
I agree with the reviewer stating that «The hypothesis suggested by L.Lobkovsky is rather a bold proposal aimed to start a discussion on alternative or additional mechanisms of climate change, specifically in the Arctic». Therefore, in this short article, I did not aim to explain the observed temperature changes throughout the Earth. It will be possible to try to do that in a special study, with application of the mechanism in question to other regions and territories. The proposed mechanism is not the only contributing factor to the warming. It is perhaps most effective in the Arctic, while for the other regions, the Arctic can play the role of a global meteorological factor, but these issues are beyond the scope of this article.
- Figure 4 shows tectonic disturbance propagation towards the Arctic. The author assumes distant propagation of perturbations with velocities of the order of 100 km/year. First, the arrow in this Figure points from Aleutian arc to the Laptev sea. This is not the area where permafrost and meta-stable gas hydrates are widely discussed in the literature (and the author does not suggest any references to prove it). The problem is discussed for the Kara Sea and the north of West Siberia where permafrost bears both gas and gas hydrates and where modeling of the related processes is ongoing.
Figure 4 is pretty general and does not target the Laptev Sea alone. The deformation disturbance wave travelling from the Aleutian arc is over a thousand kilometers wide; it covers involves all areas of the Arctic shelf and adjacent land. Therefore, the proposed trigger mechanism applies wherever the settings are suitable, i.e. in the presence of permafrost and metastable gas hydrates, including the Kara Sea as well as the northern parts of the Western and Eastern Siberia.
- In terms of impact on climate warming velocities of 100 km/year mean that the closer to the Aleutian seismic zone, the earlier will warming start shifting every year 100 km north-west! Such a phase shift should be then clearly seen in the air temperature records from respective weather stations, which are sparse but exist between Aleutian arc and Kara sea region where gas-saturated permafrost is located.
This is a fair comment, which is planned to be verified in future work, which will require a thorough analysis of all archival data for the Arctic region from the beginning of the 20th century.
- Methane release from permafrost due to stress is a good question to be discussed. The author suggests a model of permafrost consisting of a matrix and pores containing gas-saturated ice and hydrates inclusions (Fig. 5). This model is very far from the real structure of permafrost responding to stress. The matrix as follows from the scheme is considered a continuum with closed pores, but this is not the case. Particles are surrounded by adsorbed water films, pores containing not only ice and gas but also unfrozen water amount of which strongly depends on the concentration of salts. Saline sediments are exactly the case of permafrost saturated with gas. The scheme in Fig. 5 is not applicable in the case of permafrost.
I agree with the reviewer that the model presented in Fig. 5 is far from the real permafrost structure. This idealized purely mechanical model is presented in order to show the possibility of destruction of microscopic (nano-sized) pores filled with gas or fluid, due to small external stress disturbances. The destruction effect is because of the large pressure gradients emerging at the pores’ boundaries and the surrounding matrix due to the small size of the pores, even under small changes in external stresses. In the future, we plan to employ the concept of micropores’ destruction in presence of slight changes in external stresses for more realistic permafrost models, as pointed out by the reviewer.
- Lines 147-148: “When the pressure in the inclusion-surrounding matrix decreases, a high pressure gradient arises at the boundaries of the inclusions…” Why pressure in the matrix decreases?
A decrease in pressure in the matrix is a special case of a external stress state variation, caused by a deformation disturbance wave travelling within the lithosphere. Any change in a perturbed external stresses, including a decrease in pressure, is suitable for our approach. The main aspect of our model is the occurrence of a large pressure gradient at the boundaries of micropores, leading to their destruction.
- Lines 151-153: “destruction of the inclusions’ superficial zone, creating a boundary layer with elevated permeability within the inclusions ...Through this layer, gas flows from the inclusions into the permeable matrix” Why matrix is permeable? Permafrost is rather considered impermeable for water for sure, and gas – most likely.
In our idealized model, the matrix is assumed to be gas permeable. In the future, it is planned to consider more complex and adequate models of permafrost rocks, taking into account the matrix destruction as a result of seismotectonic impacts.
- References are not up to date. So many new data were obtained and laboratory experiments performed on the topic of permafrost and gas hydrates which are not mentioned in the paper. If it was limited to climate change to be caused by seismic events, it probably would cause fewer comments.
The paper focuses on a new possible seismogenic trigger mechanism of methane emission intensification and climate warming. Therefore, the numerous detailed studies of the permafrost properties were not the subject of our analysis in this case. In the future, it is planned to employ the aforementioned research to create and improved model.
Reviewer 3 Report
The author proposed a novel idea that great earthquakes in the Aleutian produce strong mechanical disturbances that propagate to the Arctic shelf and degrade hydrates in the permafrost, and this explains the abrupt climate warming phases in the Arctic.
In order to examine the idea, the author raised three questions: 1) the correlation between the rapid warming and the earthquakes in the Aleutian, 2) the mechanism of transmission of lithospheric disturbances from the Aleutian to the Arctic shelf, 3) the mechanism of hydrate degradation by seismogenic disturbance.
The correlation as question 1 is an interesting and novel finding. I am not a specialist of such air environment issue but I believe there are a lot of factors that influence the air temperature in the Arctic and some of them may explain the temperature pattern even partly. I strongly recommend the author to explain possible factors and add arguments why the earthquakes are most likely among these.
The slow transmission of lithospheric disturbances to the Arctic shelf has not been verified. The author must show evidences that such disturbances have surely reached to the potential areas of hydrate degradation at the Arctic shelf, some 2000km away from the candidate subduction margin. The author also needs to show where is the affected permafrost area by this mechanism, in Figure 4.
As the author stated, the proposed idea needs comprehensive verification and analysis, both in terms of consistency with observational data and detailed study of physical and mathematical basics of this idea. I strongly agree with the author. The current manuscript can be significantly strengthened by adding the results of these follow up studies.
Author Response
The author proposed a novel idea that great earthquakes in the Aleutian produce strong mechanical disturbances that propagate to the Arctic shelf and degrade hydrates in the permafrost, and this explains the abrupt climate warming phases in the Arctic.
In order to examine the idea, the author raised three questions: 1) the correlation between the rapid warming and the earthquakes in the Aleutian, 2) the mechanism of transmission of lithospheric disturbances from the Aleutian to the Arctic shelf, 3) the mechanism of hydrate degradation by seismogenic disturbance.
- The correlation as question 1 is an interesting and novel finding. I am not a specialist of such air environment issue but I believe there are a lot of factors that influence the air temperature in the Arctic and some of them may explain the temperature pattern even partly. I strongly recommend the author to explain possible factors and add arguments why the earthquakes are most likely among these.
Indeed, there are a number of natural mechanisms that can lead to methane emissions and climate warming, along with the well-known anthropogenic warming factor. However, this work primarily focuses on the phenomenon of a sharp warming in the Arctic, which has not yet been explained in terms of known mechanisms. Therefore, the author proposes the seismogenic mechanism associated with the great earthquakes in the Aleutian arc as the most abrupt and powerful natural factor, which, as it turned out, correlates well with the phases of a sharp climate warming in the Arctic. Other possible mechanisms of warming were not covered in this paper, since they do not exhibit the sharp variability necessary to explain the observed climate trends in the 20th and 21st centuries.
- The slow transmission of lithospheric disturbances to the Arctic shelf has not been verified. The author must show evidences that such disturbances have surely reached to the potential areas of hydrate degradation at the Arctic shelf, some 2000km away from the candidate subduction margin. The author also needs to show where is the affected permafrost area by this mechanism, in Figure 4.
The development of a rigorous mathematical model describing the disturbances’ transmission through the lithosphere from the Aleutian arc to the Arctic zone is a different, rather difficult problem, currently being solved by the author and his colleagues. The results obtained will be the subject of a distinct publication. This paper provides the references to some previous research involving deformation waves propagation in the lithosphere, and points that the characteristic velocities of propagation have the order of 100 km / year, which explains the time shift of 20 years between series of mega-earthquakes in the Aleutian arc and phases of rapid warming in the Arctic in 20th - 21st centuries. Since deformation waves in the lithosphere have a very large regional scale (front wave width of more than a thousand kilometers), they should cover all areas of the permafrost and metastable gas hydrates distribution on the Arctic shelf and adjacent onshore areas.
Round 2
Reviewer 2 Report
All the comments are already listed in review 1. The author did not make changes in that respect.
Author Response
I’d like to express my appreciation to the reviewer and acknowledge his/her will to make the study more consistent.
In response to reviewer’s request for manuscript modification, we have done some editing to the original text.
We have revised the paper, mostly in the part relating to the particular mechanism of gas release. Agreeing with the reviewer about the lack of relevance of the originally presented model of the methane release, we have replaced that with alternative concept, where the mechanical stress perturbation leads to the destruction of tiny impermeable ice films covering hydrate particles, which are known to cause the so-called hydrate self-preservation. [see references in the text]. Thus, we have modified the text within the final part of the abstract (lines 22-24), included the term “gas hydrates self-preservation” into the keyword list (line 27), and provided the description of hydrate self-preservation and ice film destruction processes, followed by gas outflow, within the paragraph 2.3 (lines 174 to 196), partly replacing the original text. Besides, we have replaced the figure 5, showing the self-preserved hydrate structure. Additional references [24] have been cited to support this model.
In the introductory part, we have inserted some statements pointing out uncorrelated nature of the anthropogenic CO2 emissions and temperature trends. (lines 40-41, 44-46).
Some further edits included moving the last text block from paragraph 2.3 to paragraph 2.1 (lines 122-130).
Also, we have appended some considerations at the end of paragraph 2.2 (lines 162-166)
