fire in the ice: methane hydrates

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Methane hydrates (Clathrates): New Fuel or Major Threat for

Increased Global Warming, Huge Slumps and Disastrous

Tsunamis?

Clathrates (methane hydrates)

• What are clathrates?• What is the origin of the methane in

clathrates?• Beasties living off decaying clathrates• Where do clathrates occur naturally?• How much clathrates are there?• Clathrates as possible fuel source• Clathrates as a cause of tsunamis/ climate

change

What are Methane Hydrates?

• Methane Hydrates are one example of ‘clathrates’

• Clathrates are compounds which consist of a ‘cage structure’, in which a gas molecule is trapped inside a cage of water molecules

• Methane (CH4) is trapped in Water (H2O) forming an “ICE”

1 m3 of hydrate -> ~170 m3 methane gas (STP)

Grey=carbon

Green=hydrogen in CH4

Red = oxygen

White= hydrogen in H2O

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Pentagonal dodecahedron

Cage made of water molecules - may contain CH4 or CO2

(a bit like a bucky ball made of Carbon)

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Origin of natural methane

• Bacterial degradation of organic matter in low-oxygen environments within sediments

• Thermal degradation of organic matter, dominantly in petroleum (e.g., Gulf of Mexico)

Where do clathrates occur?How much clathrate is there?

• Methane and water must be available (organic matter: produced by biota; in oceans: close to continents)

• Clathrate must be stable (ice): cold and/or high pressure

High latitudes (permafrost)

In medium deep sea sediments (300-2000 m)

Hydrate Stability

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Hydrate Stability

Gas Hydrate on the Sea floor

Beasties!

‘The lair of the ice worm’

Tube worms and crab

Beasties!

Organisms living on cold gas seeps

SEA WATERSO42-H2SSOrganic materialΣCO2CH4Host? MODEL OF ΣEEP CLAM BED (VAN DOVER, 2000)

coarse, porous sediment

endosymbiotic chemoautotrophic Archaeasulfate reducing Bacteria

How does the

foodchain in these ‘seep’ communities

function?

How much hydrate is there?• Estimates vary widely: globally 600,000

to 2,000,000 Tcf (trillion cubic feet)• 1 Tcf ~ 1 quadrillion Btu (quad)• World energy use (2000): about 375-400

Quad = 500 Tcf hydrate gas per year• US gas hydrates: estimated at about

100,000 to 600,000 Tcf• Gas hydrates abundant in oil-poor

countries (Japan, India)

•Clathrates as fuel:• Problems: how to collect the gas -

in a controlled way?• Small % recoverable?• Need to be treated as ‘synfuels’ to

get ‘oil-equivalent’

Climate change/Tsunamis• Methane is a strong greenhouse gas• If clathrates are destabilized, huge

amounts of methane are added to the atmosphere (55 106 years ago??)

• Sediments loose strength==>slip downslope==> slumps==> tsunamis

• Methane is rapidly oxidized to CO2, also a greenhouse gas

Have clathrates ever been destabilized in the past?

• Increase in temperature, decrease in pressure (drop sea level)

• At the end of the last ice age, mega-slumps occurred in regions with gas hydrates

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Methane hydrates:• Possibly LARGE fuel source

(natural gas): more than twice all other fossil fuels

• Unknown difficulties in recovery• Production may cause major

slumps, tsunamis, and exacerbated greenhouse effect