Received: 16 January 2019
Revised: 7 May 2019
Accepted: 11 May 2019
DOI: 10.1002/ppp.2014
Research Article
Gas‐emission craters of the Yamal and Gydan peninsulas: A
proposed mechanism for lake genesis and development of
permafrost landscapes
Yury A. Dvornikov1
|
Marina O. Leibman1,2
Alexander I. Kizyakov3
Birgit Heim6
|
|
Petr Semenov4
Alexey Portnov7
Antonina A. Chetverova8,9
|
|
|
|
Artem V. Khomutov1,2
Ingeborg Bussmann5
Elena A. Babkina1
Anna Kozachek8
|
|
|
|
Evgeny M. Babkin1
Irina D. Streletskaya3
|
|
Hanno Mayer6
1
Earth Cryosphere Institute of Tyumen
Scientific Centre SB RAS, Tyumen, Russia
Abstract
2
This paper describes two gas‐emission craters (GECs) in permafrost regions of the
Tyumen State University, Tyumen, Russia
3
Lomonosov Moscow State University,
Moscow, Russia
4
I.S. Gramberg All‐Russia Scientific Research
Institute of Geology and Mineral Resources of
the World Ocean (VNIIOkeangeologia), Saint‐
Petersburg, Russia
5
Alfred Wegener Institute Helmholtz Centre
for Polar and Marine Research, Germany
6
Yamal and Gydan peninsulas. We show that in three consecutive years after GEC formation (2014–2017), both morphometry and hydrochemistry of the inner crater lakes
can become indistinguishable from other lakes. Craters GEC‐1 and AntGEC, with initial depths of 50–70 and 15–19 m respectively, have transformed into lakes 3–5 m
deep. Crater‐like depressions were mapped in the bottom of 13 out of 22 Yamal
lakes. However, we found no evidence that these depressions could have been
Alfred Wegener Institute Helmholtz Centre
for Polar and Marine Research, Potsdam,
Germany
formed as a result of gas emission. Dissolved methane (dCH4) concentration mea-
7
(45 ppm on average). Yet, the concentration of dCH4 from the near‐bottom layer of
School of Earth Sciences, The Ohio State
University, Columbus, Ohio
sured in the water collected from these depressions was at a background level
lake GEC‐1 was significantly higher (824–968 ppm) during initial stages. We
8
Arctic and Antarctic Research Institute, Saint‐
Petersburg, Russia
established that hydrochemical parameters (dissolved organic carbon, major ions, iso-
9
Saint‐Petersburg State University, Institute of
Earth Sciences, Saint‐Petersburg, Russia
topes) measured in GEC lakes approached values measured in other lakes over time.
Correspondence
Yury Dvornikov, Earth Cryosphere Institute,
Tyumen Scientific Centre, Siberian Branch of
Russian Academy of Sciences, Tyumen, Russia.
Email: ydvornikow@gmail.com
that potentially resulted from gas emission. Temperature profiles measured in GEC
Funding information
Russian Science Foundation, Grant/Award
Number: 16‐17‐10203; Russian Foundation
for Basic Research (RFBR), Grant/Award
Numbers: 18‐05‐60222 and 18‐05‐60080
below might take place. However, with the present data we cannot establish the
Therefore, these parameters could not be used to search for Western Siberian lakes
lakes show that the water column temperatures in GEC‐1 are lower than in Yamal
lakes and in AntGEC – close to values of Gydan lakes. Given the initial GEC depth
> 50 m, we suggest that at least in GEC‐1 possible re‐freezing of sediments from
modern thickness of the closed talik under newly formed GEC lakes.
K E Y W OR D S
gas‐emission craters, gydan, lakes, methane, yamal
1
|
I N T RO D U CT I O N
Glacial periods characterized by significantly lower air temperatures
allowed the development of thick onshore and offshore permafrost.1
During the Quaternary, the West Siberian Arctic underwent consecu-
Maximum permafrost development occurred during the Last Glacial
tive glacial–interglacial and marine transgression–regression stages.
Maximum (~20 ky BP). The modern Kara Sea shelf (>120 m b.s.l.)
Permafrost and Periglac Process. 2019;1–17.
wileyonlinelibrary.com/journal/ppp
© 2019 John Wiley & Sons, Ltd.
1
2
DVORNIKOV
ET AL.
was in suberial conditions and therefore the Yamal peninsula was char-
funnel‐shaped top.9 The first field expeditions to GEC‐1 in 2014
acterized by a more continental climate. On the Yamal peninsula, ter-
described the surrounding landscape of the area, provided morpho-
restrial permafrost has been sustained throughout the Late
metric descriptions of GEC‐1 and proposed an origin of this landform
Pleistocene, although ground temperatures increased during the Holo-
as resulting from the emission of methane from permafrost.7,9-11
cene climatic optimum, and temperatures then decreased following
Later, more accurate morphometric parameters of GEC‐1 were
this stage (<3 ky BP). Therefore, the majority of modern permafrost
defined.12,13 Geophysical surveys using electrical‐resistivity tomogra-
on the Yamal peninsula is of Late Pleistocene age (≤ 20 ky BP). The
phy techniques revealed a possible layer of gas hydrates at a depth
Yamal–Gydan area is today characterized by continuous permafrost
of 60–80 m and established the base of permafrost at depths of
up to 450 m thick with ground temperatures varying between −1
160–180 m surrounding GEC‐1.14
and −9°C and with average ice content 30–50% of the total volume.
2
Decomposition of gas hydrates and associated explosive gas emis-
A specific feature of the cryolithological conditions of the area is a
sion was proposed as one of explanantions for this crater's appear-
wide distribution of tabular ground ice (TGI) and cryopegs in the geo-
ance.15 An alternative hypothesis proposed that GEC‐1 formed as a
3,4
logical section.
Being impermeable to gas, permafrost generated sig-
result of the collapse of a large pingo formed after lake drainage
nificant gas storage in the form of free gas and in the form of gas
allowing the existing sub‐lake talik (a layer of year‐round unfrozen
hydrates. Recent climate warming in the Arctic5 has led to increases
ground in permafrost areas) to re‐freeze accompanied by the growth
in ground temperatures and active layer thickness,6 triggering release
of cryogenic hydrostatic pressure.16 Based on SPOT‐5 and Landsat‐8
of shallow gas accumulations from the upper permafrost layer.
satellite images, the eruption date of GEC‐1 was narrowed to an inter-
For the first time in the terrestrial permafrost environment, gas
val between October 9 and November 1, 2013.12 According to infor-
emission craters (GECs) have been observed on the Yamal7 and
mation provided by the local Nenets community, AntGEC formed on
8
Gydan peninsulas in summer and autumn 2014 (Figure 1). The Yamal
October 27, 2013.17 Satellite data analysis revealed that a mound
GEC (69.9711 N, 68.3703°E), 42 km from Bovanenkovo gas field, was
45–58 m in diameter and 5–6 m in height existed before the forma-
named GEC‐19 and the Gydan GEC near Antipayuta settlement
tion of GEC‐1, and was named mound‐predecessor (MP).12 Before
(69.7946 N, 75.035° E) was named AntGEC.8 Initially, these two
AntGEC formation, MP had base diameter of 20 m and height of only
permafrost‐related features were deep and relatively narrow
2 m. Expansion of this mound led to a blowout of ground ice and sed-
cylinder‐shaped depressions with subvertical frozen walls and a
iments over a radius of up to 300 m.8,12,17-19 Therefore, such blowouts
FIGURE 1 Studied objects: (b) map of GEC‐1 and AntGEC location; (b) photo of GEC‐1 taken from helicopter in July 2014 by M. O. Leibman; (c)
photo of AntGEC October 21, 2013 by K. S. Okotetto. Dashed line –Obskaya–Bovanenkovo railway, dotted line –Bovanenkovo–Ukhta gas
pipeline, black rectangle – planned development of Gydanskoe gas field, black triangle – planned development of Salmanovskoe gas field and
Arctic LNG‐2 infrastructure [Colour figure can be viewed at wileyonlinelibrary.com]
DVORNIKOV
3
ET AL.
can be hazardous for existing infrastructure on the Yamal peninsula
evolution of GEC‐1, from the initial void (summer 2014) to the mod-
and planned infrastructure on the Gydan peninsula (Figure 1). For
ern shallow lake (summer 2017).
example, GEC‐1 is located near the Bovanenkovo–Ukhta gas pipeline
and Obskaya–Karskaya railway, as well as migration routes and
camping places of indigenous reindeer herders. This makes the study
2
MATERIALS AND METHODS
|
of GECs critically important both for the scientific community and
2.1
for future development of this region.
|
Bathymetry of GEC lakes and Yamal lakes
Ongoing GEC studies will help to identify areas of potential gas
blowouts, which in turn will help to prevent possible infrastructure
Bathymetric surveys of GEC lakes were performed (2015, 2017 – GEC‐
collapse and provide recommendations for industrial development in
1, 2016 – AntGEC) to establish the bottom structure of newly formed
permafrost regions. Moreover, GEC studies will provide a significant
basins and their dynamics. Bathymetric measurements were performed
contribution to a paleo‐permafrost knowledge database, including
using a Humminbird 788cxi chartplotter (vertical accuracy ±0.1 m) with
novel insight into past evolution of permafrost landscapes of the West
echo sounder and internal GPS receiver installed on a boat, in calm
Siberian Arctic.
weather conditions, or by lead line. Source data were processed using
Lakes are abundant in Yamal and Gydan. Lakes cover on average
20
10% of the Yamal peninsula,
reaching 20% on floodplains of large
HumView software: depth values were extracted at 5 second intervals,
corrected for signal noise. Sounding point data were gridded in ESRI
About 90% of all lakes
ArcGIS 10 to obtain bathymetric maps with a spatial resolution of
Since our first observations, it
1.5 m. In addition to the GEC lakes, detailed bathymetric maps of 22
became evident that GECs could potentially evolve into new lakes,
Yamal lakes were obtained during surveys in 2012–2017 using
21
rivers such as Mordy‐Yakha and Se‐Yakha.
2
22
are small (<1 km ) water bodies.
Despite the
Humminbird 788cxi chartplotter (see ref.23 for details). Crater‐like
prevailing hypothesis that the majority of Yamal lakes have resulted
depressions in lake bottoms were delineated using bathymetric maps
9,11
which would be unrecognizable from other lakes.
the occurrence of GEC features has
and slope maps. Depression slope polygons were defined as areas with
allowed us to hypothesize that gas emission has played some role
a local, abrupt break in slope. The base of lake‐bottom depressions (cra-
in the initial stages of lake formation on the Yamal and Gydan pen-
ter‐like features) were delineated as flat areas with slopes of 0–2°.
from thermokarst processes,
21
9
insulas during the Holocene. To test this hypothesis, we analyzed a
number of hydrochemical parameters both for GEC lakes and other
2.2
|
Hydrochemistry of lake water
“normal” lakes of the Yamal and Gydan peninsulas in order to find
similarities between them and to establish specific hydrochemical
Water samples for hydrochemical analyses were collected from
features of GEC lakes that could be used to search for other lakes
newly formed GEC lakes and other Yamal and Gydan lakes within
that have possibly appeared as a result of gas emission.
six winter and summer field campaigns during 2015–2017. Samples
Hydrochemical features include methane concentration, isotopic sig-
on Yamal were collected from 25 lakes located near Bovanenkovo
natures of the lake water, lake water chemistry and temperature
settlement (Figure 1a). On Gydan, samples were collected from five
regimes. Specifically, we wanted to test the following: if methane
and 14 lakes located near the settlements of Gyda and Tazovskiy
has played an important role in GEC occurrence, the methane source
respectively (Figure 1a).
might have provided elevated dissolved methane concentrations in a
Water samples were collected from both the upper layer (0–30 cm
newly formed lake; how strong are the dynamics of methane con-
below the water surface) of the water body and from the bottom layer
centration in GEC lakes over the years and what is the potential
(50–100 cm above the bottom) using a TD‐Automatika hydrological
source of methane?; what is the main water source in GEC lakes –
water sampler. Bottom layer water samples were collected in most
thawed ground ice or atmospheric precipitation and do the water
cases from the deepest areas of the lake, or in the lake center from
isotopic composition and water chemistry differ from other lakes?;
the rubber boat. Samples from the upper layer were collected from
what are the current temperatures of the GEC lake water and how
the shore or using the boat. During winter field campaigns, lake ice
does this influence further talik development under GEC lakes or,
drilling was performed to collect under ice water samples. In total,
otherwise, allow the sediments infilling these lakes to be re‐frozen?
we collected 112 water samples from all lakes.
It was important to trace the dynamics of hydrochemical parameters
of GEC lakes which may also contribute to the mentioned research
question regarding the origin of lakes in Western Siberian as we
2.2.1 | Dissolved methane concentration and isotopic composition (δ13C and δD)
do not know how fast can GEC lakes can come to resemble a “normal lake” in terms of hydrochemistry. Apart from the hydrochemical
Water samples for dissolved CH4 (dCH4) concentration were collected
parameters, we have also compared detailed bathymetry of GEC
in 120 ml glass serum bottles (flushed several times with sample water
lakes with the bathymetry of 22 Yamal lakes to find the evidence
to ensure no contact with the atmosphere), capped with black rubber
that gas emissions have occurred within modern basins of existing
stoppers and sealed with an aluminum crimp. To prevent further
lakes on the Yamal peninsula. Since the initial GEC are clearly a very
microbial oxidation of CH4, 65% HNO3 was added to each sample.
dynamic objects in terms of geomorphology, we also present the
Glass bottles and rubber stoppers are relatively methane‐tight and
4
DVORNIKOV
acidification of water samples results in good long‐term sample pres-
2.2.5
|
ET AL.
Temperature profiles
ervation,24,25 but we cannot exclude the possibility that some CH4
was lost from the samples. CH4 concentrations were determined by
Water temperature was measured every 2 m throughout the water
gas chromatography in two laboratories: AWI Helgoland (2015) and
column using a KrioLab logger with an accuracy of ±0.1°C. Tempera-
VNIIOkeangeologia Saint‐Petersburg in 2016–2017. Detailed infor-
ture loggers were immersed in the water column for at least 20 min
mation on the determination of dCH4 in water samples is given in
until complete stabilization of the temperature values.
Methods S1.
Carbon and hydrogen stable isotopes (δ13C, δD) of CH4 were analyzed in ISOLAB b.v. with an Agilent 6890N GC (Agilent Technologies)
3
RESULTS
|
interfaced to a Finigan Delta S IRMS using a Finigan GC‐C II interface.
Samples were calibrated regularly against a calibration standard and
3.1
|
Bathymetry of GEC lakes
results are reported in permil vs. vPDB. Minimum CH4 concentrations
for stable isotope measurements were approximately 40 and 300 ppm
Bathymetric maps were produced for GEC‐1 lake based on 2015 (Fig-
for carbon and hydrogen, respectively.
ure 2a,b) and 2017 surveys (Figure 2c,d). The bathymetric map of
AntGEC lake is based on 2016 survey (Figure 2e,f). In 2015, GEC‐1
was characterized as a rounded, U‐shaped hollow with a diameter of
2.2.2 | Stable water isotopes from Yamal, Gydan and
GEC lakes
approximately 48 m, a maximum depth of 23 m, and we observed high
Stable water isotopes (δ18O, δD) were determined using mass spec-
summer 2017, GEC‐1 lake had become a drainage lake with an appar-
trometry in two laboratories. Samples from 2015 were analyzed with
ent inlet and outlet. The neighboring LK‐001_CR lake (Figure 2a) pro-
a Finnigan MAT Delta‐S mass spectrometer (AWI Potsdam). Samples
vided the upstream source area (Figure 2c). Area and water volume in
from 2016 and 2017 were analyzed with a Picarro L2120‐i analyzer
2017 were 0.55 ha and 14,320 m3 respectively, the maximum mea-
at the Climate and Environmental Research Laboratory of Arctic and
sured depth was 4.9 m, and the mean depth was 2.3 m. The relatively
Antarctic Research Institute in Saint‐Petersburg. Results were
flat bottom and steep sidewalls formed a bowl‐shaped lake basin (Fig-
expressed in delta per mil notation (δ, ‰) relative to the Vienna Stan-
ure 2d).
dard Mean Ocean Water (VSMOW) standard.
ice content permafrost in the crater walls (Figure 2b). The lake surface
area and water volume were 0.23 ha and 21,128 m3 respectively. By
In 2016, AntGEC lake (Figure 2e) was likewise characterized as a
rounded U‐shaped hollow (Figure 2f). The maximum measured depth
was only 3.6 m and mean depth 1.7 m. Area and water volume were
2.2.3
|
Dissolved organic carbon
Water samples for dissolved organic carbon (DOC) were filtered
0.099 ha and 1643 m3 respectively.
3.2
|
Bathymetry of Yamal lakes
through Whatman glass‐fiber filters of 0.7 μm pore size in the field
and acidified with ~30 μl of 30% HCl to prevent microbiological con-
The maximum measured depth among the studied Yamal lakes (Table
version. They were stored in cold conditions until processing with a
1) varied broadly from 1.8 m in typical thermokarst lakes (eg LK‐010)
Shimadzu TOC‐VCPH in the Otto‐Schmidt Laboratory (Saint‐Peters-
to 23.2 m in a lake located close to an area with near‐surface TGI dis-
burg) using the method of high‐temperature combustion of
tribution (LK‐015). Two of the lakes were deeper than 20 m (LK‐008,
nonpurgeable organic compounds (NPOCs). The accuracy of this
LK015). However, the average measured depth in all lakes was 2.9 m.
method is 10%. Additional information on DOC measurements and
Thirteen lakes had crater‐like local depressions in their bottoms (Table
calculation in given in Methods S1.
1). These depressions typically had steep slopes (8.1° on average,
although some slopes exceeded 36°) which is evident from depth profiles across the entire lake (Figure 3). The area of all the crater‐like
2.2.4
|
depressions within a lake including slopes was relatively small com-
Major ions
pared to the entire lake area (0.93–18.4%, Table 1).
Water samples for major ions were filtered through Sartorius
cellulose‐acetate (CA) filters of 0.45 μm pore size. Samples for cation
3.3
|
Hydrochemistry of lake water
analysis were further acidified with 65% HNO3 to prevent adsorptive
accretion. Samples were then processed using ion‐chromatography in
the Otto‐Schmidt Laboratory on a Methrom 761 Compact IC (2015–
3.3.1 | Dissolved methane concentration and isotopic composition (δ13C and δD)
2016) and in VNIIOkeangeologia on a Methrom 940 Professonal IC
Vario equipped with conductometry detector (2017). Results in the
−1
The concentration of dCH4 was obtained for Yamal lakes and GEC‐1
form of total concentrations (mg L ) and equivalent % (eq%) were
lake in 2015 (summer) and 2017 (early spring, summer). dCH4 data are
processed within RStudio software.
presented in Figure 4. In 2015, data for 23 Yamal lakes were obtained
DVORNIKOV
5
ET AL.
FIGURE 2 Photos and bathymetry of
studied GEC lakes: (a) GEC‐1 lake in the
background, and lake LK‐001 CR in the
foreground, August 15, 2015 (photo Yu.
Dvornikov); –(b,d) bathymetry of GEC‐1 lake
(September 1, 2015 and September 5, 2017,
respectively), dashed grey circle on (d) shows
GEC‐1 area in 2015; –(c) UAV orthophoto
map on September 5, 2017, red arrows
represent the drainage pathway of the lake
LK‐001 CR; –(e) AntGEC lake on August 30,
2016 (photo A. Khomutov); –(f) bathymetry of
AntGEC lake (August 30, 2016) [Colour figure
can be viewed at wileyonlinelibrary.com]
including nine lakes for which upper and bottom water were sampled.
In August–September 2017, water samples from 25 Yamal lakes
The concentration of dCH4 among all samples varied from 0 to
were collected including 14 lakes with upper and bottom layer sam-
92 ppm with a median value of 7.9 ppm (n = 23). Values for the bottom
pling. Concentrations of dCH4 varied from 6.24 to 37.03 ppm (median
layer varied from 1 to 56 ppm with a median value of 1.8 ppm (n = 9).
12.86, n = 25) for upper layer samples, and from 3.03 to 100.58 ppm
Measured dCH4 concentrations in the GEC‐1 lake water from the upper
(median 14.22, n = 14) for the bottom layer samples (depth range 4–
layer and from 14.4 m depth were 45 and 824 ppm, respectively.
20 m). Concentrations of dCH4 measured in the GEC‐1 lake water from
In April 2017, water samples for six Yamal lakes were collected. In
the upper layer and 4 m depth were 2.5 and 2.0 ppm, respectively.
two lakes (LK‐001, LK‐006) water was sampled from two depths. Lake
Samples with dCH4 concentrations of at least 41 ppm (n = 10)
ice thickness varied from 1.25 to 1.5 m and the upper layer samples
were used to measure δ13C values and samples exceeding 100 ppm
were collected from a depth of 3 m. Samples from three lakes (LK‐
(n = 5) were used to measure δD values. In addition, three TGI samples
002, LK‐012, LK‐016) were considered as bottom layer samples
from GEC‐1 walls collected in September 2015 were added to this
because of their shallow depths (2, 6, 4.5 m, respectively). Concentra-
dataset.26 Values of δ13C were within the range −84.5 to −48.7‰
tions of dCH4 varied from 3.27 to 3.98 ppm at 3 m depth (n = 3), and
(n = 13), while δD values ranged from −398 to −258‰ (n = 8, Table
from 2.11 to 809.19 ppm at the bottom (3–15 m) layer (n = 5). Con-
2). For GEC‐1, TGI and water samples taken in this study revealed sim-
centrations of dCH4 measured in the GEC‐1 lake water at depths of
ilar isotopic values for δ13C and δD (−70 to −85‰ and −364 to
3 and 8 m (ice thickness 1.3 m) were 438 and 968 ppm, respectively.
−378‰ respectively). In contrast, in Yamal lakes δ13C and δD values
6
DVORNIKOV
TABLE 1
ET AL.
Characteristics of Yamal lakes: Bathymetry and bottom structure
Lake ID
Area (ha) Longitude Latitude Mean depth (m) Max. depth (m) Number of depressions Depression area (ha/% of the lake area)
LK‐001
37.16
68.8829
70.2787
4.4
16.9
LK‐002
3.23
68.9045
70.2977
1.1
2.3
3
3.43/9.2
LK‐003
118.61
69.0019
70.2898
1.1
10.6
1
2.54/2.1
LK‐004
73.64
68.9705
70.2809
LK‐006
3.61
68.8991
70.2878
2.7
12.3
10
2.36/3.2
4.2
12.8
LK‐007
38.18
68.9912
LK‐008
41.88
68.8110
70.2672
3.1
10.8
2
0.37/1.0
70.2760
5.5
20.7
2
4.82/11.5
LK‐010
4.25
68.8642
70.3012
0.6
1.8
LK‐012
LK‐013
2.22
68.9216
70.2825
3.2
7.3
1
0.17/7.6
212.46
68.8843
70.2563
1.5
9.2
4
1.97/0.93
LK‐014
6.62
68.8736
70.2836
4.8
14.2
2
0.17/2.6
LK‐015
9.92
68.9218
70.2651
7.4
23.2
2
1.83/18.4
LK‐016
10.77
68.9335
70.2668
2.3
5.1
LK‐017
6.97
69.0221
70.2326
3.5
9.4
1
0.51/7.3
LK‐018
12.85
69.0061
70.2319
2.3
7.8
LK‐019
15.16
68.9951
70.2301
1.9
6.3
1
0.76/5.0
LK‐031
59.20
69.1860
70.2760
2.2
8.4
5
4.15/7.0
LK‐035
65.19
68.8738
70.2155
1.8
10.8
3
6.28/9.6
LK‐037
2.03
68.9938
70.2498
3
5.7
LK‐038
4.09
68.9974
70.2448
2.4
5.5
LK‐039
2.69
69.0024
70.2494
1.8
3.8
0.91
68.3676
69.9718
1.2
2.5
2.9
9.7
23
4.9
LK‐001 CR
Average
34.8
–
–
GEC‐1 (2015)
GEC‐1 (2017)
0.23
0.55
68.3703
69.9711 12.7
2.3
AntGEC (2016)
0.1
75.035
69.7946
1.7
2.8
2.3/6.6
3.6
were heavier, ranging from −48 to −67‰ and from −258‰ to
characterized by a gradual progressive increase in the heavy fraction
−288‰ respectively. In 2015, the δ13C values from GEC‐1 water
content from 2014 to 2017 (Figure 5). Water of AntGEC lake had
were similar to the surrounding TGI. In 2017, however, they were
δ18O values of −17.8 and −17.6‰ and δD values −136.9 and
closer to the values obtained for Yamal lakes.
−135.2‰ from 3 m depth and the upper layer, respectively.
3.3.2 | Stable water isotopes from Yamal and Gydan
lakes and GEC lakes
3.3.3
|
Dissolved organic carbon
The concentration of DOC in GEC‐1 lake water was 50.3 mg/L
Stable water isotope (δ18O, δD) data show a wide range of values. Fig-
in September 2015 samples. It decreased to 12.9/13.3 mg/L (upper
ure 5 shows δ18O and δD values plotted against VSMOW. Melted TGI
layer/bottom layer) in April 2017, and further decreased to9.1/
has a lighter composition with δ18O values generally lower than
9.3 mg/L in September 2017 (only 18.3% of the 2015 value).
−20‰ and δD values lower than −140‰. In contrast, water collected
DOC in Yamal lakes varied from 3.5 to 7.3 mg/L (n = 24) in 2015,
from lakes of Central Yamal and Gydan typically has δ18O values
from 3.7 to 36 mg/L in April 2017 and from 2.7 to 5.1 mg/L in summer
higher than −15‰ and δD values generally higher than −115‰ (Fig-
2017. No significant difference in DOC concentration was found
ure 5). Water from GEC lakes occupies an intermediate position
within the water column of Yamal lakes: ±0.4, ±0.8 and ±1.3 mg/L in
(δ O values between −20 and −15‰ and δD values between −150
August 2015, April 2017 and August–September 2017 respectively.
and −115‰). Water collected from GEC‐1 in different years is
Lower DOC concentrations were measured in lakes in summer 2017
18
DVORNIKOV
7
ET AL.
FIGURE 3 Digital terrain models of lake basins and catchments: –(a,b,c) lakes LK‐003, LK‐012 and LK‐015, respectively (Table 1), elevations are
given in Baltic height system; (d) lake depth profiles, blue dots and numbers indicate elevation of water level [Colour figure can be viewed at
wileyonlinelibrary.com]
FIGURE 4 Distribution of dCH4 concentrations in water (blue rectangles) of Yamal lakes and GEC‐1 lake. Red symbols indicate samples collected
in summer (August–September), blue – early spring (April). Triangles – 2015 data, circles – 2017 data. Dark blue rectangles represent ice thickness
in April. Gray shading indicates sediments filling GEC‐1 in 2015 [Colour figure can be viewed at wileyonlinelibrary.com]
compared to summer 2015: DOC in 21 out of 23 lakes was 22%
DOC was on average 40.9% higher in six sampled lakes, with the dif-
lower, varying in a range between 6 and 53.9%. Two lakes (LK‐017
ference varying between 17.1 and 87.3%.
and LK‐031) were characterized by higher DOC in summer 2017 (by
The estimated DOC concentration in AntGEC lake in 2016 was
9.9 and 20.5%, respectively). A stronger seasonal difference was
8.8 mg/L, while in five Gydan lakes DOC varied between 3.4 and
observed between April and August–September 2017. In April 2017,
12.8 mg/L (7.3 mg/L on average).
8
DVORNIKOV
TABLE 2
ET AL.
Concentration and isotopic composition of dCH4collected from TGI, water of Yamal lakes and GEC‐1 lake
Sampling object
GEC‐1
Yamal lakes
Object ID
Sampling depth
Date
TGI 15Yd 2/4i
TGI 15Yd1/11i
TGI 15Yd1/12i
GEC‐1 lake
Ice wall
14.4 m
3.0 m
8.0 m
Sept. 1, 2015
Sept. 2, 2015
Sept. 2, 2015
Sept. 1, 2015
April 16, 2017
April 16, 2017
LK‐001
LK‐010
LK‐025
LK‐002
LK‐006
LK‐012
LK‐016
11.8 m
0.3 m
0.3 m
1.6 m
11.0 m
4.0 m
3.0 m
Aug.
Aug.
Aug.
April
April
April
April
18,
17,
30,
12,
12,
12,
14,
dCH4 (ppm)
δ13C vs PDB (‰)
δD vs SMOW (‰)
Source
1620.2
807.7
2099.2
824.0
438.3
968.2
−70.7
−84.5
−70.3
−75.6
−59.0
−60.1
−364
−371
−378
−350
−394
−398
26
46.1
92.0
41.9
809.2
289.9
259.7
552.6
−51.5
−54.1
−56.8
−58.9
−59.1
−48.7
−67.0
‐
‐
‐
−258
‐
‐
−288
2015
2015
2015
2017
2017
2017
2017
This study
Na++K+ > Mg2+ > Ca2+. The proportion of HCO3− in GEC‐1 decreased
through three sampling iterations: 74, 55.7 and 24 eq% in samples
taken in summer 2015, winter 2017 and summer 2017, being replaced
by Cl− through time, the proportion of which consistently increased in
a sequence 17.7, 35.4 and 59 eq% respectively. During summer 2015
and 2017, the proportions of anions remained stable in Yamal lakes
with an average of 56.7 eq% Cl−, 36.7 eq% HCO3− and 5.4 eq%
SO42− (2015, n = 24) and 53.2 eq% Cl−, 43.9 eq% HCO3− and
2.7 eq% SO42− (2017, n = 25). The proportions of cations remained
stable during summer 2015 and 2017, reflecting the general Na++K
+
> Mg2+ > Ca2+ scheme for the entire dataset. During winter 2017,
Yamal lakes had higher proportions of Cl− (89.4 eq%) among anions
and Na++K+ (86.1 eq%) among cations.
In 2016, the proportion of Cl− in AntGEC lake was higher (41 eq%)
compared with HCO3− (32.2 eq%) and SO42− proportion (24.1 eq%).
The proportion of HCO3− was much higher than in other Gydan lakes
(in only one lake out of five was the proportion higher than zero). Specifically for AntGEC lake and Gydan lakes the general scheme Na++K
+
FIGURE 5 Stable isotopes (δ O, δD) of tabular ground ice (black
dots,26), water from lakes (Yamal, blue dots; Gydan, green dots).
Isotopes for water from GEC‐1 are represented by red triangles with
the following sampling dates: 1 – September 2014,26 2 – September
2015, 3 – April 2017, 4 – September 2017. Samples from AntGEC are
shown with yellow triangles, data from August 2016 (5) [Colour figure
can be viewed at wileyonlinelibrary.com]
> Mg2+ > Ca2+ remained undistinguishable.
18
3.4
|
Temperature profiles
Water column temperature profiles were obtained in AntGEC and
Gydan lakes in summer 2016 (Figure 6a), as well as in GEC‐1 and
Yamal lakes in April and summer 2017 (Figure 6b). Complete mixing
of water masses was observed in summer in all Yamal and Gydan
3.3.4
|
Major ions
lakes, except for GEC lakes where some evidence of stratification
was observed. In summer 2017, GEC‐1 upper and bottom layers dif-
Given the marine origin of deposits in the area, major anions are dom−
inated by Cl (56.7 eq% on average among all samples, n = 62). The
proportion of anions among all samples was in the order Cl
−
> HCO3− > SO42− except the Gydan lakes where the proportion of
SO42− was higher than that of HCO3−.
fered by 1.16°C (4.97°C at 4.9 m and 6.13°C in the upper layer, measured on September 5, 2017).
In AntGEC, the upper and bottom layers differed by 1°C (8.8°C in
the upper layer and 7.8°C at 3.6 m, measured on August 30, 2016).
The temperature difference in all lakes did not exceed 0.5°C between
+
+
Cations are strongly dominated by Na +K (58.5 eq% on average
the upper layer and the bottom layer of the water column, including
among all samples, n = 62). The proportion of cations was in the order
deep (>20 m) lakes (eg LK‐015). Inverse stratification was observed
DVORNIKOV
9
ET AL.
FIGURE 6 Temperature profiles recorded for AntGEC and two Gydan lakes (a) as well as for GEC‐1 and Yamal lakes (b) [Colour figure can be
viewed at wileyonlinelibrary.com]
in Yamal lakes in April 2017. The temperature of the upper layer in
4.2
Hydrochemistry of GEC lakes
|
these lakes was close to zero (0.02–0.77°C) while at the bottom water
temperatures reached 3.36°C (LK‐006). At the same time, no stratifi-
4.2.1
|
CH4 source in GEC lakes
cation was observed in GEC‐1 lake (−0.02°C in the upper layer and
GEC‐1 lake was characterized by elevated dCH4 concentration in the
−0.11°C at the bottom).
bottom water layer in summer 2015 and early spring 2017 (824 and
968 ppm respectively). Values of dCH4 were 4–50 times higher than
4
DISCUSSION
|
in Yamal lakes: 16 ppm on average based on the 2015 dataset and
241 ppm on average based on the early‐spring 2017 dataset. We
4.1
Morphological features of newly formed GEC
lakes
assume that methane release was active for at least two years after
In 2014, the initial depth of GEC‐1 was more than 50 m9 and the
gas bubbling within the newly formed water body that was filled with
depth of AntGEC was 15–19 m.8 After the appearance of GECs in
river water immediately after the gas emission event.27 However, in
October 2013,8 filling of the craters with rain water, melted snow,
the GEC‐1 lake, we did not observe any gas bubbles in 2015 or in
thawed ice and sediment from the retreating crater walls initiated
2017. Presumably, gas is continuously delivered from the gas‐
the formation of new lakes. As a result of GEC‐1 lake expansion, the
saturated sediments under the lake and further oxidized in the water
parapet of GEC‐19 was barely visible in 2016, due to the processes
column. The extensive filling of the newly formed lakes with sedi-
of collapse and inundation. Similarly, the crater of AntGEC was barely
ments from the retreating walls of GEC‐1 and AntGEC8,9 implies that
recognizable. Therefore, we conclude that the GEC lakes transformed
initial gas flows can be restrained by a thick and relatively imperme-
|
appearance of the crater.
Field observations in the Se‐Yakha GEC area documented active
into a more common lake morphology over three consecutive summer
able layer of silty–clayey and sandy sediments. Given average ground
seasons. This process is controlled by the topography of the area and
temperatures around the GEC‐1 area of −1 to −5°C28 we assume fur-
lithology (ie sediment composition and texture) where the craters
ther freezing of sediments from below under the GEC‐1 lake, probably
were formed. Our data show that GEC‐1 decreased significantly in
forming a seal for further gas flows from beneath. On the other hand,
depth (maximum depth 23 m in September 2015 and 4.9 m in Septem-
we expect the development of a talik at the bottom of GEC lakes.
ber 2017, Figure 2b,d). Despite the increase of GEC‐1 lake area by
Given a water temperature of GEC‐1 lake close to 0°C (Figure 6b)
0.1 ha in two years, due to the retreating crater walls (22% increase
and bottom temperature of 7.5–8°C in AntGEC lake (Figure 6a), we
from the initial area in 2015) and despite additional drainage of lake
might expect faster talik development at the bottom of AntGEC lake.
LK‐001_CR into GEC‐1 lake (11,742 m3 of water), GEC‐1 lake had a
However, with the present data we cannot establish a modern bound-
lower water volume in 2017 (14,320 m3) than in 2015 (21,128 m3)
ary between frozen and thawed sediments under these two new lakes.
Our dataset on methane isotopes suggests that the source of
due to this significant filling of the crater with sediments.
8,18
In the case of AntGEC, which formed on the edge of a terrace,
methane is primarily microbial (Table 2), as the values of δ13C are, in
the newly formed hollow quickly filled with sediments (maximum
general, less than −60‰29 which is also consistent with the data pre-
depth of AntGEC lake in 2016 was only 3.6 m, Figure 2f), while the
sented by Buldovicz et al.16 Values of δ13C in methane extracted from
lower south‐facing slope of AntGEC limited further accumulation of
deep boreholes of Bovanenkovo gas field (depths 28–120 m) vary
water. Therefore, AntGEC lake contained only 1643 m of water in
from −74.6 to −70.4‰, also suggesting a microbial origin.30 Similarly,
2016.
methane released due to decomposition of methane hydrates
3
10
DVORNIKOV
ET AL.
extracted from a 451 m borehole in Taglu gas field (Canada) from
(3.7 mg/L). The abrupt decline in DOC in GEC‐1 lake, from 50 mg/L
depths of 56.9–354.3 m has shown δ13C values between −90 and
in summer 2015 to 9.2 mg/L in summer 2017, significantly exceeded
−78‰, and δD values between −314 and −162‰, again suggesting
the seasonal and yearly DOC fluctuations in other Yamal lakes (Figure
31
7), and other West Siberian lakes.50
microbial methane.
Our data do not support the hypothesis that methane from deep
We observed the highest seasonal DOC concentrations in the shal-
sources was responsible for GEC‐1 formation, as suggested in a num-
low thermokarst lakes (eg LK‐016), where DOC in April can be twice
ber of publications.11,32,33 Continuous permafrost serves as an imper-
as high as in August. Larger, deep lakes such as LK‐001 and LK‐015
30,34-36
meable seal for the migration of gases from deep horizons,
show more stable seasonal DOC fluctuations. In 2016, we found that
although it was also suggested that thermogenic methane can migrate
DOC concentration in AntGEC lake (8.8 mg/L) was on the same order
to the upper horizons in Western Siberia.37 In a discontinuous perma-
of magnitude as in Gydan lakes (7.3 mg/L), and therefore AntGEC lake
frost area of the Mackenzie Delta, bubbles of thermogenic methane
is indistinguishable from other Gydan lakes. We found no evidence of
38
Moreover, gas bubbles
peat inclusions in AntGEC remaining walls and we therefore assume
persisted in lakes throughout the year, preventing formation of the
the lower amount of allochtonous organic matter source available
lake ice in winter (K. Kohnert, pers. comm.). The concentration of
for AntGEC lake compared to GEC‐1 lake.
were documented on a lake surface.
CH4 in the gas phase of Yamal's TGI can reach up to
39,40
The cryogeochemical model of the cryolithological section in cen-
Therefore, methane dissolved in GEC‐1 lake may in
tral Yamal4,51 implies several horizons formed due to consistent epige-
part originate from the gas phase of ice melted out of crater walls.
netic freezing of marine sediments in subaerial conditions after marine
However, the observed essential difference in dCH4 with depth in
regression. The geological section comprises a layer of marine clays
GEC‐1 during summer 2015 and spring 2017 (Figure 4) supports the
underlain by mostly sandy sediments containing highly mineralized liq-
suggestion that methane seeps in the bottom sediments are con-
uid water (cryopegs) at different depths and TGI bodies at the clay–
nected to some initial methane source.
sand interface.51 The water chemistry of Yamal lakes is dominated
23,000 ppm.
Records from deep boreholes in the area of Bovanenkovo gas field
by Na+ and Cl− ions reflecting the marine origin of the sediments.
(42 km north of GEC‐1) drilled in the 1990s have revealed a number of
The predominance of HCO3− in GEC‐1 lake may be related to TGI.
notable gas (87–99% CH4) blowouts, with average flow rates of 500
This has also been described by Olenchenko et al.14 Yamal TGI bodies
3
3
30,41
m /day and reaching 14,000 m /day.
Blowouts mainly occurred
with low mineralization (<0.2 g/kg) may exhibit this dominance of
at depths 60–120 m in silty sediments with 2–3 cm thick sand layers
HCO3− anions.52 This is caused by the genetic transformation of the
enriched with organic matter.34,42 Gas blowouts have been also
initial seawater source into TGI.53
observed to the south of the study area (Yuribey river, Southern
43
Yamal) from depths less than 60 m.
The proportion of HCO3− in TGI from the GEC‐1 walls at different
Therefore, we conclude that
horizons exceeds 45 eq% at 18.6 m depth and can reach 81 eq% at
microbial methane formed due to decomposition of gas hydrates
5.8 m depth.26 The dominance of HCO3− was also documented in
was the most likely source of gas in GEC‐1.9,14,44,45
other TGI bodies of Central Yamal.54 Total mineralization of water
from GEC‐1 (211.4 mg/L, 2015) and AntGEC (185 mg/L, 2016) lakes
4.2.2 | Water source in GEC lakes and lake water
chemistry
is close to the range of TGI mineralization from GEC‐1 crater walls,
with values ranging from 10 to 180 mg/L.26 TGI found within the
Se‐Yakha and Mordy‐Yakha river valleys had a similar mineralization
Lakes are natural reservoirs collecting material from surrounding
catchments.46 Lake hydrochemistry reflects the geochemistry of the
constituent bedrock and sediments of the lake catchment. Newly
formed GECs are not an exception and these water bodies hold a geochemical signal of surrounding sediments. Furthermore, frozen crater
walls contribute to the temperature regime of the water column.
The concentration of DOC in GEC lakes is controlled by the supply
of allochtonous organic matter delivered from surrounding areas,47
peat layers and scattered organic matter in frozen deposits. A trend
of increasing organic matter concentration within lake waters has
been observed as a result of recent formation of thermocirques.48
The concentration of DOC in water extracted from peat layers of
thermocirque exposures can reach 243 mg/L.49
Based on two years of observations (see section 3.3.3), we found
that the decreased rate of crater wall thawing and retreat as well as
potential dilution by atmospheric precipitation has led to further
DOC decline in GEC‐1 lake. DOC concentrations in GEC‐1 lake in
2017 were of similar magnitude (9.2 mg/L) as in other Yamal lakes
FIGURE 7 Seasonal dynamics of dissolved organic carbon (DOC) in
Yamal lakes
DVORNIKOV
11
ET AL.
range of 26–176 mg/L51 and TGI from Bovanenkovo gas field expo-
explained by the more complex topography and higher topographic
sures exhibited a mineralization range of 9.7–168 mg/L.54
gradient, potentially allowing more terrestrial material to be
Analysis of isotopes (Figure 5) also supports the hypothesis that
transported into lakes from catchments,48 as well as the presence of
thaw of TGI can provide a considerable source of the water in
mineralized marine clays in the geological section.51 Notably, Yamal
55
GEC‐1 and AntGEC lakes.
At the initial stage (2014), the isotopic
lakes with adjacent thermocirques (Figure 8a) have a higher concen-
composition of GEC‐1 was closer to the isotopic composition of
tration of all ions including HCO3− probably due to the input of melted
TGI found within GEC‐1 and other exposures on the Yamal penin-
water and sediments from retreating thermocirque walls.49,56
sula (Table 3). We therefore conclude that in the first stages of
The seasonal hydrochemical dynamics of GEC‐1 were different
GEC formation the lake water source is dominated by thawed TGI.
from other sampled Yamal lakes. The high concentrations of major
Later, atmospheric precipitation and runoff from a neighboring lake
ions in winter water samples implies the saturation of unfrozen
dilute the water, and the isotopic composition approaches −15 to
water by salts, and isolation from atmospheric precipitation and ter-
−11‰ for δ O and −115 to −90‰ for δD measured in Yamal
restrial input. This results in an increase of Na+ and Cl− ions, up to
and Gydan lakes (Figure 5, Table 3) as well as the average values
90 eq% on average. In the following summer, an increase in
of δ18O and δD for summer precipitation in the Yamal region
HCO3− can be observed in Yamal lakes, but this was not observed
(−12.5 and −96‰ respectively,54).
in GEC‐1 lake: in summer 2017, the proportion of HCO3− in GEC‐
18
The overall proportion of mineralized elements in GEC‐1 lake does
1 lake had declined further. We link this to the decreased geochem-
not differ significantly from the sampled subset of Yamal lakes (Figure
ical input from TGI in summer 2017 and lake water input from
8a). On the other hand, the mineralization in AntGEC is one order of
drained lake LK‐001 CR. The total mineralization of GEC‐1 lake
magnitude higher than in Gydan lakes and in lakes near Tazovskiy set-
has increased in summer 2017 (300 mg/L) compared to winter
tlement (Figure 8b). The higher mineralization of Yamal lakes com-
2017 (190 mg/L). Therefore, in terms of hydrochemistry GEC‐1 lake
pared to Gydan lakes (with AntGEC as an exception) can be
has transformed to a “normal lake.”
TABLE 3 Isotopic composition of GEC lakes, Yamal and Gydan lakes, tabular ground ice from exposures found in Yamal, and atmospheric
precipitation
Object
δ18O (‰)
δD (‰)
Reference
GEC‐1 (2014)
−19.8
−149.6
26
GEC‐1 (2017)
−16.1 to −15.8
−122 to −118
This study
AntGEC (2016)
−17.8 to −17.6
−136.9 to −135.2
This study
TGI (GEC‐1 walls)
−20.6
−152.4
26
TGI (Marre‐Sale, west Yamal)
−18 to −17
−160 to −130
26
TGI (Mordy‐Yakha, central Yamal)
−23.2 to −21
−172.9 to −162.7
54
TGI (se‐Yakha, central Yamal)
−20.5 to −17.9
−150.2 to −137.5
54
Yamal and Gydan lakes
−15 to −11
−115 to −90
This study
Yamal (summer precipitation), average
−12.5
−96
54
FIGURE 8 Concentration of ions in lake water: –(a) Yamal lakes and GEC‐1 lake (2017 W and 2017 S in winter and summer); (b) Gydan and
Tazovskiy lakes and AntGEC lake. Mineralization of Tazovskiy lakes – unpublished data. All lakes are divided into several groups: lakes with
stable coasts, lakes with adjacent thermocirques,49 and floodplain lakes flooded in spring48 [Colour figure can be viewed at wileyonlinelibrary.com]
12
DVORNIKOV
4.3 | Origin of crater‐like depressions in the bottom
of Yamal lakes
ET AL.
With the present data we cannot establish an exact origin of all
mapped depressions. Multiple origins of crater‐like depressions
reported in the literature are plausible.
In Western Siberia, crater‐like depressions have been observed at the
bottom of West Siberian lakes and termed gas‐explosion craters.37,57
These craters were mapped in Yamal to identify degassing hot spots
potentially related to deeper hydrocarbon formations.10,11,32,58 How-
4.4 | Mechanisms of GEC formation and future
landscape evolution
ever, neither gas composition and concentration in these features
nor morphometry were discussed in these publications. Kuzin et al.37
Crater‐like depressions were first observed in the marine environ-
suggested that the occurrence of such features possibly results from
ment on the Nova Scotian Shelf (North Sea) in the late 1960s, and
gas advecting from deep sources (thermogenic CH4) and argue that
these were named pockmarks.62 Further studies led to detailed char-
they are often observed within oligotrophic “blue lakes” characterized
acterization of such structures in submarine conditions63 and con-
by low pH, and lack of phyto‐ and zooplankton.
cluded that pockmarks are formed due to gas release from the
However, we have observed such crater‐like depressions in Yamal
seafloor and therefore present a significant methane source.61
lakes that cannot be considered as “blue lakes.” These features are
Despite the fact that both West Siberian craters and submarine
not visible on satellite images or from a helicopter given the consider-
pockmarks are conditioned by the process of gas release, theories
able water depth and sometimes high turbidity.59 Detailed bathymet-
regarding their mechanisms of formation differ. Pockmarks gener-
ric surveys in 22 lakes revealed several depressions (Table 1) having
ated in submarine conditions form as a result of consistent gas
either a circular or elongated shape close to lake shores with different
release, which disturbs soft bottom sediments on centennial to mil-
morphology: from absolutely flat terrain (eg LK‐003) to high cliffs (eg
lennial timescales. In contrast, craters on Yamal were generated
LK‐012). Such depressions are 10–20 m deep relative to the bottom
extremely rapidly in subaerial conditions, due to short and rapid epi-
of the lakes, and have steep slopes (>36°, 8.1° on average). For Yamal
sodes of permafrost‐bounded gas outburst.
lakes, crater‐like depressions have also been linked to thaw of TGI
21
and are often associated with elevated shores.
The closest offshore analogs of the modern GECs can be found on
Similarly, in the
the South Kara Sea shelf, where hundreds of buried ancient
Canadian Arctic, lake‐bottom depressions were reported as being
thermokarst structures have been recently mapped based on seismic
connected closely to shores with active or stable retrogressive thaw
data.64 These subsea structures reach tens of meters in depth and
slumps.60 Water depths on these shores were on average 4 m greater
are acoustically transparent, probably due to the collapsed, unconsol-
than stable undisturbed shores. Therefore, these depressions were
idated sediments infilling them, which is in good agreement with the
associated with lake bottom subsidence due to enlargement of taliks
observations from Yamal and Gydan craters.
under lakes caused by ground temperature increases.60 Given that
Kizyakov et al.12 showed that before the GEC‐1 appeared, a 5–6 m
the base of TGI on Yamal may be located as low as 21.2 m b.s.l. in
high and 45–58 m wide mound existed at that location. Similarly, a
3
Yamal and the minimum elevation of all mapped depressions reached
2 m high and 20 m wide mound preceded the emergence of AntGEC
only 12 m b.s.l., it is possible that depressions have been formed as a
on the Gydan peninsula.8 Similar mounds were previously described
21,60
result of TGI degradation.
Alternatively, depressions could result
in the submarine environment as pingo‐like features (PLFs): in the
from microbial gas flows or blowouts from permafrost, contrary to
Beaufort Sea,65 and Barents–Kara Sea shelves 5–9 m in height and
deeper source migration, previously suggested by Kuzin,37 and
70–1000 m in diameter,36,66 and on the Pechora Sea shelf showing
33
Bogoyavlenskiy et al.
Low dCH4 concentrations measured in the
base diameters from 20 to 1000 m and heights of 5–25 m. The drilling
water sampled in crater‐like depressions (20–60 ppm, Figure 4) can
of one of these PLFs in the Pechora Sea led to the blowout of a large
be explained by depletion of gas storages. This was probably the case
amount of gas from a depth of 49.5 m and failure of the drilling equip-
for GEC‐1: in summer 2017 the dCH4 concentration was only 2–
ment.67 The concentration of microbial methane in sediments col-
3 ppm (Figure 4).
lected from the flank of a PLF in the Kara Sea exceeded
Similar forms (pockmarks) have been previously observed in sub-
120,000 ppm.66 The source of the gas that creates overpressure in
marine environments around the world where they are related to
the PLFs is either decomposition of methane hydrates,65 or gases
61
the release of free gas from the seafloor into the water column.
Sub-
accumulated within lenses of thawed sands located below the base
marine pockmarks vary significantly in shape and size, with depths
of submarine permafrost.67 Gas‐bearing sediments have also been
from 1 m to several tens of meters, diameters reaching hundreds of
revealed in the South Kara Sea shelf at the clay–sand interface.68,69
meters and slopes as steep as 30°.
There are at least two main hypotheses for the origin of PLFs: (a) they
An alternative hypothesis for the formation of depressions implies
formed under subaerial conditions during the Pleistocene and are ana-
former river/stream valleys, as these depressions are sometimes elon-
logs of terrestrial pingoes (bulgunnyakhs), and then became inundated
gated and connected to lake inlets or outlets. Several channel‐like
during Holocene transgression; and (b) they were formed in submarine
depressions have been mapped on the bottom of Yamal lakes (eg
conditions (36 and references therein). Given the start of formation of
LK‐018, LK‐031). Retrieval of deep sediment cores from local sub‐lake
the GEC‐1 mound‐predecessor in the Here the right reference is 17
depressions is required to further clarify their origin.
(Arefyev et al. 2017)1940s,17 it is rather a modern process.
DVORNIKOV
ET AL.
13
Based on the results of GEC studies and related submarine ana-
70 m b.s.l. in the continuous permafrost. This gas might further
logs, we propose a conceptual model for GEC formation and evolu-
migrate and accumulate within a cryotic layer of saline sediments that
tion. This model may also help to determine potential scenarios of
can often be observed at 25–35 m b.s.l. on Yamal.51 This is also sup-
future landscape development in permafrost regions (Figure 9). In
ported by documented gas blowouts from depths of 70–120 m30 dur-
the terrestrial and nearshore environment, methane originates from
ing drilling of boreholes in Central Yamal, mainly from sandy coastal–
shallow intrapermafrost gas occurrences or relic gas hydrate reser-
marine deposits.70 Gas flows can create pressure in areas with the
voirs43 within the relic gas hydrate distribution zone deeper than
development of TGI at the clay–sand interface,51 which results in
FIGURE 9 Possible gas escape mechanisms in the terrestrial and nearshore environment originating from decomposed gas hydrates (a) and
stages of GEC‐1 formation (b,c,d). Relic gas hydrate reservoirs (1,43) within the relic gas hydrate occurrence zone (RGHOZ) stored in the
continuous permafrost (2) can be a potential free gas (3) source that can be stored within unfrozen cryopegs (4) widely distributed at depths of
25–35 m b.s.l. on the Yamal peninsula.51 This is supported by documented gas blowouts mainly from depths of 70–120 m (5,30) during drilling of
boreholes (BH) in central Yamal. Gas flows (6) can create a pressure (7) in areas with tabular ground ice (TGI) occurrence (8) at the clay (9) – sand
(10) interface,51 which results in the development of a mound‐predecessor (MP) on the ground surface (b) and pingo‐like features (PLFs) (11) –
documented analogs in the nearshore environment.36,66 An inncrease in active layer thickness (12) may lead to the formation of gas‐emission
craters (GECs) (c,9) which are then filled (13) with sediments from crater walls (14). These new layers of sediments >50 m then re‐freeze (d)
preventing further gas escapes from permafrost. The base of permafrost is derived from,14 geological section for central Yamal is modified after.51
GEC characteristics are taken from.9 Elevation is given in meters above and below sea level in a Baltic system [Colour figure can be viewed at
wileyonlinelibrary.com]
14
DVORNIKOV
ET AL.
the development of a mound‐predecessor in the terrestrial environ-
proportion of atmospheric precipitation in GEC‐1 lake from
ment (Figure 9b) and PLFs in the nearshore environment.36,66
2014 to 2017.
An abnormally warm summer in the Arctic in 2012 increased the
6. Yamal lakes are characterized by higher DOC in winter compared
active layer thickness in the Yamal peninsula.71 This weakened the
to the end of summer. In GEC-1, however, we observed a gradual
upper frozen layer which we infer would have contributed to GEC for-
DOC decline from 2015, reaching a similar level as in other lakes,
mation.9 The GEC was further infilled with collapsed sediments from
which suggesting the stabilization of constant organic matter input
the crater walls (Figure 9c). This new >50 m thick sediment layer is
from retreating crater walls and dilution by atmospheric precipita-
likely to refreeze from below, preventing further gas release from per-
tion. In turn, the concentration of major ions is increasing in GEC‐1
mafrost (Figure 9d).
lake, becoming closer to that in Yamal lakes. The concentration of
major ions in AntGEC lake water was one order of magnitude
5
|
higher than in Gydan and Tazovskiy lakes.
C O N CL U S I O N S
7. Known ground temperature for the GEC‐1 area and measured
The data collected from the GEC‐1 and AntGEC sites as well as from
temperature regime of GEC‐1 and AntGEC lakes suggest that, at
Yamal and Gydan lakes showed that many lakes in the West Siberian
least in GEC‐1, a thick layer of modern sediments filling its hollow
Arctic may have origins that are potentially similar to GECs: a hollow
(>50 m) has undergone further re‐freezing from below. In summer
formed as a result of intensive gas emission. This process can also
2017, the bottom temperature of GEC‐1 lake was two‐fold lower
be involved in shaping the lake basins, as residual gas emission at
than in Yamal lakes due to the surrounding frozen walls. This may
the lake bottom is common even after the major episode of gas
slow down the development of the talik, at least under GEC‐1
outburst.
lake. Further geophysical studies are required to define the thickness of unfrozen sediments. The refreezing of sediments from
1. GEC lakes transformed into lakes over three consecutive summer
below can potentially prevent further gas seepage into the water
seasons. This process is controlled by the topography and lithology
column, resulting in a decrease in dissolved methane concentra-
of the area where the craters were formed.
tion in the water of new lakes, as has already been observed in
2. Yamal lakes are characterized by local (1–18% of the lake area)
GEC‐1 lake (summer 2017 data). AntGEC walls covered by sandy
crater‐like depressions on their bottom (more than 50% of mea-
talus prevent direct contact between lake water and frozen
sured lakes). These depressions have an average slope of 8.1°
deposits, and thus the lake's water column exhibits a higher over-
(reaching 36°). Our data do not show whether these crater‐like
all temperature. This can potentially lead to faster talik develop-
depressions originate from gas emission or from the thaw of tabu-
ment and to thinning of the lower layer that is impermeable to
lar ground ice. Moreover, these depressions can be interpreted as
escaping gas.
paleo‐stream valleys. Retrieving lake sediment cores is required to
clarify the origin of each depression.
We analyzed diverse datasets from this permafrost region in order to
explain the mechanism of GEC formation. In the terrestrial and near-
Hydrochemical analyses of GEC lakes also suggests that three years
shore environment, methane originates from intra‐permafrost gas
can be enough for the GEC water column to become indistinguishable
accumulations or relic gas hydrate reservoirs within the relic gas
from other lakes. Our monitoring data suggest that the dynamics of
hydrate distribution zone deeper than 70 m b.s.l. in the continuous
several hydrochemical parameters in GEC lakes differ from the sea-
permafrost. This gas further migrated and accumulated within a layer
sonal and yearly dynamics of these parameters in other lakes.
of cryotic saline deposits that are often observed at 25–35 m b.s.l.
on the Yamal peninsula. The accumulated methane created pressure
3. At the first stage of new lake formation, a high dissolved methane
in areas with TGI at the clay–sand interface, which resulted in the
concentration of microbial origin characterizes the water column,
development of a mound‐predecessor. As pressure within this
especially bottom layers.
mound‐predecessor exceeded the confining strength of the overlying
4. A higher concentration of methane in the bottom layer indicates
substrate, a GEC erupted.
that the source of methane is from beneath the TGI rather than
from the frozen deposits of the crater walls and TGI itself, although
it is characterized by a high methane concentration as well.
5. The isotopic composition of the water as well as major ions of
ACKNOWLEDGEMENTS
This work was supported by Russian Science Foundation (RSF) grant
GEC‐1 lake water suggest that thawed TGI is a dominant water
No. 16‐17‐10203 and partially supported by Russian Foundation for
source at the first stage of GEC formation. The isotopic compo-
Basic Research (RFBR) grants No. 18‐05‐60080 and 18‐05‐60222.
sition of GEC lake water is quite close to the specific composi-
We thank Otto Schmidt Laboratory for Polar and Marine Research
tion of TGI. The water of GEC lakes was also characterized by
(OSL) for providing laboratory facilities. We also thank two anony-
−
a higher proportion of HCO3 anions, which is also a common
mous reviewers and the editor for valuable comments and improve-
signature of TGI. We observed a gradual increase in the
ments to the manuscript.
DVORNIKOV
15
ET AL.
ORCID
Yury A. Dvornikov
https://orcid.org/0000-0003-3491-4487
Marina O. Leibman
https://orcid.org/0000-0003-4634-6413
Artem V. Khomutov
https://orcid.org/0000-0001-8855-3483
Alexander I. Kizyakov
Ingeborg Bussmann
Birgit Heim
https://orcid.org/0000-0003-4912-1850
https://orcid.org/0000-0002-1197-7461
https://orcid.org/0000-0003-2614-9391
Alexey Portnov
https://orcid.org/0000-0003-4930-8308
Irina D. Streletskaya
Anna Kozachek
Hanno Mayer
https://orcid.org/0000-0001-5645-8772
https://orcid.org/0000-0002-9704-8064
https://orcid.org/0000-0003-4129-4706
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SUPPORTING INFORMATION
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Supporting Information section at the end of the article.
How to cite this article: Dvornikov YA, Leibman MO,
Khomutov AV, et al. Gas‐emission craters of the Yamal and
Gydan peninsulas: A proposed mechanism for lake genesis
and development of permafrost landscapes. Permafrost and
Periglac
ppp.2014
Process.
2019;1–17.
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