63 / 78
A GLOBAL OUTLOOK ON METHANE GAS HYDRATES
63
Sedimentary layers and gas migration pathways
for the continental margin and slope o shore Svalbard
Predominantly hemipelagic
and other marine sediment
Predominantly
glacigenic sediment
Hemipelagic interbeds
Bubble plumes
Gas pocket
Base of GHSZ
Gas
Gas
1000
900
800
700
600
500
400
300
200
100
0
Depth (m)
Old top of GHSZ
Old base
of GHSZ
Fractures
Gas released by
dissociating
hydrate
GHSZ
Base of former GHSZ
0
1
2
3
4
5 Km
EAST
WEST
Figure TB-3.1.2:
Sedimentary layers and gas migration pathways for the continental margin and slope offshore Svalbard. In this conceptual
model, gas cannot easily reach the sediment surface of the continental slope without being transformed to gas hydrates or diverted
upslope by impermeable hydrate-bearing sediment or glacial debris flows. Instead, gas migrates up through faulted sediment and upslope
through permeable layers before reaching the sediment surface in the gas-flare region near the top of the continental slope (adapted from
Thatcher
et al.
2013).
3.1.2, inset). It has been postulated that hydrate had been stable in
shallower waters, but a 1°C bottom water temperature increase over
the past ~30 years caused that hydrate to begin dissociating and
emitting methane from the sea floor (Thatcher and Westbrook 2011;
Sarkar
et al.
2012). Marin-Moreno
et al.
(2013) have extended this
idea to predict the regional methane release over the next 300 years.
They use two different climate models to estimate the distribution of
hydrates in the region, and assuming hydrate dissociation is driven
by long-term temperature increases, they estimate anywhere from
~1 – 25 TgC (0.001 – 0.025 GtC) could be released per year from the
section of sea floor between 400 – 550 metres water depth along the
Eurasian Margin over the next 300 years. Recent observations from
the MASOX autonomous observatory, however, suggest the methane
plumes may be thousands of years old, having already begun hosting
biologic communities that have formed carbonate deposits. Rather
than resulting frommodern warming trends, the plumes may instead
come from methane hydrates that form and dissociate in response
to seasonal temperature changes of the bottom water (Berndt
et al.
2014). In spite of the many observed plumes, the methane released
from the sea floor contribute a negligible amount of methane to the
atmosphere (Fisher
et al.
2011), but will instead likely contribute to
acidification and oxygen depletion in the ocean.
This region remains an active study area as researchers continue
to investigate the origins and fate of methane in this location. Our
understanding of this system will evolve rapidly over the next few
years as results are released from ongoing studies, as well as from
several new research cruises.