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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.