FROZEN HEAT | Volume 1

Sedimentary layers and gas migration pathways for the continental margin and slope o shore Svalbard

0 Depth (m)

Gas released by dissociating hydrate

Bubble plumes

100

Old top of GHSZ

Base of former GHSZ

200

GHSZ

Old base of GHSZ

300

Hemipelagic interbeds

Fractures

400

500

Gas

Predominantly glacigenic sediment

Predominantly hemipelagic and other marine sediment

600

Base of GHSZ

Gas

700

800

Gas pocket

0

1

2

3

4

5 Km

900

WEST

EAST

1000

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.

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 63