the authors of this paper seem like a collection of smug ignoramuses.
I suspect this is the pot calling the kettle black. This paper is mainly a review of existing knowledge regarding methane hydrate characteristics distribution and stability as should be evidenced by the unusually large list of references (~400 papers).
Carolyn Ruppel is the Chief of the USGS Gas Hydrates Project and has been in that position for the last 6 years, previous to which she hs been a professor of geophysics at Georgia Institute of Technology and was a visiting professor at MIT. She has a list of just over a hundred publications to her credit a large proportion of which deal with the topic of hydrates. I find it difficult to imagine there is anyone more qualified to comment on the state of knowledge of hydrates than the head of the USGS program.
John Kessler is a professor at University Rochester where he is active in investigating chemical oceanography emphasizing isotopic biogeochemistry studies looking into methane and carbon dioxide dynamics in ocean systems. He previously held professorship in the Department of Oceanography at Texas A&M and was an Alfred P Sloan Reseach Fellow in Ocean Sciences. He has a list of 33 refereed publications many of which deal with methane flux from oceans. His background puts him in the ideal place to talk to sources of methane release, one of the main issues when trying to determine what has actually come from hydrate dissociation.
1) Clathrates are associated with biological CH4 production. There are exceptions, such as the Yamal peninsula were it is clear that clathrates are formed by gas seeps from gas reservoirs, but they are not very important
Perhaps you have read a completely different paper ….the authors of this paper state exactly that:
Owing to the concentration of organic carbon on continental margins, these locations are where most gas hydrates occur (Figure 3), and gas hydrates are largely absent beneath abyssal plains. The organic carbon is delivered to the sediment both by the rain of phytoplankton to the seaﬂoor in highly productive continental margin waters and by export of terrestrial sediment from the continents. Remineralization of sedimentary organic carbon produces CO2, and most CH4 formed in sediments by microbial processes is the result of reducing this CO2. Microbial CH4, instead of thermogenic CH4 formed at higher temperatures via the same processes responsible for conventional natural gas, is the type most often found in recovered gas hydrates
2) Ocean biotic activity is concentrated in coastal zones due to the availability of essential nutrients and other ecosystem reasons. So clathrates (and carbon) accumulate mostly over coastal seabeds and not inner ocean seabeds
Perhaps you can quote from the paper where you think they got it wrong? The distribution of methane hydrates globally as determined by direct observation or from boreholes, seismic etc is shown in a map in the paper. As well Table 2 points out the data which was previously published indicating that a full 95.3% of methane gas in place in hydrates is located in the Deep Marine geographic setting.
3) The Siberian shelf has an average depth of 50 meters which is not deep enough to preclude CH4 emissions to the atmosphere and there is plenty of evidence of CH4 evading to the surface. The fuss over whether this evasion is becoming catastrophic is not the issue. Other shelf regions will of necessity contain clathrate deposits that will be sufficiently shallow as to outgas into the atmosphere.
The main point of the paper is that there is little actual evidence for release of methane from hydrates and that estimates of the amount of hydrates is problematic given less than adequate knowledge about how much pore space is actually occupied by methane and whether or not many of the identified hydrates from seismic and other means other than direct observation are are indeed hyrates.
Some relevant quotes from the paper:
Some researchers do infer large amounts of PAGH beneath arctic continental shelves (e.g., 35 Gt C in hydrate beneath the Laptev Sea shelf) [ Shakhova et al., 2010a] ,but several assumptions used in making this estimate may not fully account for the complexity of PAGH systems. Shakhova et al. [2010a] also invoked anomalous shallow gas hydrates beneath the East Siberian Arctic shelf as a potential CH4 source and to explain elevated estimates of CH4 sequestered in gas hydrates. This area was not glaciated at the LGM, as is usually required for shallow gas hydrates to occur, and the origin and existence of possible anomalous gas hydrate deposits remain controversial and require further examination
Despite the expectation that upper continental slopes host the most climate-susceptible gas hydrate populations, widespread upper slope seepage has so far only been recognized on the West Spitsbergen margin [Westbrook et al., 2009], the U.S. Atlantic margin [Skarke et al., 2014], and the northwestern U.S. Paciﬁc margin[Johnson et al., 2015]
Upper continental slope seepage on the other margins has been interpreted in terms of warming of intermediate waters on time scales of years to centuries [Berndt et al., 2014; Biastoch et al., 2011; Brothers et al., 2014; Ruppel,2011a; Stranne et al., 2016b], but so far only the West Spitsbergen margin seepage has been ﬁrmly linked to dissociating gas hydrate [Berndt et al., 2014]