luni, 6 aprilie 2015

GOING AMOK BY AMOC ......impact of AMOC on Arctic Sea Ice and Atmosphere Hea t Transport into the Arctic Rong Zhang, GFDL/NOAA, Princeton, NJ, USA, Rong.Zhang@Noaa.Gov The observed decline trend in September Arctic sea ice extent (SIE) since 1979 has often been attributed in large part to the increase in greenhouse gases . The observed decline trend and future projections of ice - f ree summer bring up the potential for trans - Arctic shipping in the near future . However , the detail mechanisms causing the low frequency variability of su mmer Arctic SIE is still unclear. T he most rapid observed decline actually occurred during the recent hiatus in global warming , and CMIP5 multi - model ensemble mean response to changes in radiative forcings exhibit much less decline trend in September Arcti c SIE, but stronger warming trend in global mean surface temperature than that observed during this hiatus period . In this study, it is shown that AMOC and the associated poleward Atlantic heat transport have played a significant role in the low frequency variability of summer Arctic SIE using the GFDL couple d climate model . At low frequency the March Barents Sea SIE anomaly is dominated by anti - correlated Atlantic inflow anomaly, thus is also significantly correlated with September Arctic SIE a nomaly. The observed March Barents Sea SIE has a very similar normalized decline trends as the observed September Arcti c SIE from 1979 to 2013, consistent with an increasing trend in Atlantic inflow and the multidecadal variability of AMOC implied by its f ingerprints over the same period . This study estimated that a positive trend in the Atlantic inflow have contributed a substantial portion o f the obser ved summer Arctic sea ice extent decline trend since 1979 . The results also provide a clue of why most CM IP underestimate the observed summer Arctic SIE decline in recent decades which might have been substantially affected by internal variability. If the AMOC and the associated Atlantic heat transport into the Arctic were to weaken in the near future, then t here would be a slowdown in the decline trend of September Arctic SIE, and we may not have ice - free Arctic summer that soon in a few decades. This plausible scenario with enormous social and economical impacts cannot be ignored. This study also shows that a t low frequency , changes in poleward atmosphere heat transport across the entire Arctic Circle are compensating to and dominated by AMOC induced Atlantic heat transport anomalies into the Arctic, hence a stronger AMOC and associated enhanced Atlantic hea t transport into the Arctic ocean leads to both reduced summer Arctic SIE and reduced poleward atmosphere heat transport into the Arctic. Most of the anomalous heat transported into the Arctic region by the Atlantic Ocean is released into the atmosphere, t hen transported southward out of the Arctic region by the anomalous atmosphere heat transport. Previous studies attribute the observed changes in the atmosphere circulation pattern and eddy heat transport in recent decades to the observed Arctic sea ice de cline. However, i f the recent observed Arctic sea ice decline since 1979 is also accompanied by strengthened AMOC and enhanced Atlantic Ocean heat transport into the Arctic Ocean, then changes in the atmosphere circulation pattern and eddy heat transport m ight have been dominated by the response to enhanced poleward Atlantic Ocean heat transport, not dominated by Arctic sea ice decline


POSITION 69 OR SO of the pdf.

 It is established that permafrost prevents
the migration of methane from deep-seated
hydrocarbon collectors into the upper
permafrost and to the surface [Skorobogatov
et al, 1998; Rivkina et al, 2006]. Concentration
of methane in frozen Quaternary deposits
in the Arctic depends on the age, origin
and lithology of the permafrost. The gas
and gas-hydrate accumulations are localized
in the organic-rich horizons [Rivkina and
Gilichinsky, 1996; Rivkina et al., 2006].
The authors’ main hypothesis for the crater’s
formation involves the decay of relict gashydrate
inclusions, the release of gas out of
initially frozen deposits enclosing cryopegs
and tabular ground ice. This assumption
is based on the known cryolithology and
geochemistry of permafrost in the region,
with most of the studies performed in
the Bovanenkovo gas field investigations
[Streletskaya and Leibman, 2003]. The
Bovanenkovo studies revealed substantial
gas concentrations [Chuvilin, 2007; Yakushev,
2009], which are blocked by the permafrost
[Rivkina et al., 2006; Gilichinsky et al., 1997].
The possibility of the release of the gas
from the collectors near the surface is
shown by methane and hydrogen sulfide
effusion under the Barents and Kara seas
from 70 to 130 m beneath the sea floor
[Rokos, 2009]. Boreholes at Bovanenkovo gas
field [Chuvilin, 2007] revealed various gas
manifestations, such as emission out of the
borehole and high content in the samples,
in the depth interval 20 to 130 m. Most of
the gas was contained in ice-bearing clays
[Yakushev, 2009]. These clays also enclosed
tabular ground ice, cryopegs and some voids
filled with low-density ice. The maximum gas
emission was 14,000 m3/day [Bondarev et
al., 2008]. F. Are (1998) also suggests that gas
accumulates in voids within the permafrost.
Studies of gas bubbles in tabular ground
ice of the Kara sea region have shown
concentrations of methane exceeding that
of the atmosphere by an order of magnitude
[Lein et al., 2003; Leibman et al., 2003;
Streletskaya et al., 2014; Vanshtein et al.,
2003]. Analysis of δC13(CH4) in the upper
layers of permafrost in Bovanenkovo area
returns results around – 70 ‰, indicating
a biochemical origin of this gas in organic
matter in the permafrost. [Bondarev et al.,
2008]. The isotopic composition is within the
same range as in tabular ground ice bubbles
[Lein et al., 2003; Vanshtein et al., 2003;
Cardyn et al., 2007; Streletskaya et al., 2014].
Methane concentration in modern marine
sediments may exceed 1 ml/l in the Arctic
seas, [Mironyuk and Otto, 2014] while even
more than 0.1 ml/l is considered a high
concentration [Hovland et al., 2002]. The
methane concentration measured in the
frozen deposits of coastal exposures on the
Yamal can reach 1.7 ml/kg and in tabular
ground ice even more, as much as 2.2 ml/kg
[Streletskaya et al., 2014].
The release of this gas could be triggered
by changes in ground temperature.
Ground temperature changes result from
fluctuations in both air temperature and
snow accumulation. Warmer air can trigger
the rapid changes on the surface, thaw
ground ice bodies and create thermal
denudation landforms (thermocirques)
and thermokarst lakes. Probably, the new
features found in 2014 result from the same
rise of air temperature, but presenting a new
mechanism of formation: gas release in the
Thus the origin of the Yamal crater
hypothesized in this paper is based on the
analysis of (a) existing features resulting
from gas-release processes in the Kara sea
region as analogues of the observed onshore
landform, (b) climate fluctuations that
could have caused changes in thermal state
of permafrost, and (c) comparison to other
landforms connected to tabular ground
ice, the salinity of the deposits, and the
concentration of organic matter.
The central part of the Yamal Peninsula is
limited by the Yuribei River in the south
and the Nadui-Yakha River in the north,
including areas of active gas extraction and
transportation. The region is in the zone of
continuous permafrost at least 300 m thick,
with high tabular ground ice content. In
the 2000s, noTable fluctuations of various
climatic parameters have been observed
(Table 1).
The summer of 2012 and the preceding
winter of 2011–2012 were the warmest
since 2006 (Table 1). Summer precipitation
in 2012 was close to the maximum level for
this period, though precipitation during the
preceding winter was at a medium level.
The crater is located in the Tundra bioclimatic
zone, a subzone of typical tundra, about
17 km west of the Mordy-Yakha River and
about 11 km south of Halev-To Lake (69°58’N
and 68°22’E). Rolling hills with altitude up to
52 m have gentle slopes descending to small
ravines and lakes. The slopes are densely
vegetated by willow shrubs up to 1.5 m high.
Cryogenic landslides have disturbed the lake
shores (Fig. 1). The crater is located on a small
hill about 34 m above sea level.
The crater area is within the zone of
continuous permafrost. The average
ground temperature may be as low as –6
°С, and the active layer is up to 1 m deep.
The geological section is represented by
silty-clayey deposits, rich in ice and organic
matter, bearing several layers of tabular
ground ice several meters thick (Ananieva,
1997, Fig. 2).
Table 1. Main climatic controls of the thermal state of permafrost according
to weather station Marre-Sale records (

The date of
the crater’s formation is estimated to have
been in the late fall of 2013; (5) The high
concentration of methane in the hole, which
decreases in the vicinity of the hole and is
negligible far from the hole, indicates the role
of methane in the formation of the crater;

Un comentariu:

  1. The average
    ground temperature USED TO be as low as –6
    °С, and the active layer is up to 1 m deep.
    The geological section is represented by
    silty-clayey deposits, rich in ice and organic
    matter, bearing several layers of tabular
    ground ice several meters thick (Ananieva,