Investigation
9B:
9B - 1
methane Hydrates:
major implications FOR CLIMATE
Driving Questions: What are methane hydrates? What role might methane hydrates
have played in causing the PETM (Paleocene/Eocene Thermal
Maximum) and what were the possible impacts on atmospheric
and ocean carbon dioxide levels? Are there similarities between
PETM and current anthropogenic loading of carbon dioxide in the
atmosphere and ocean?
Educational Outcomes: To describe methane hydrates and how they can impact
concentrations of carbon dioxide in the atmosphere and ocean. To examine any similarities
between what happened during the PETM and the current upward trends in atmospheric and
oceanic carbon dioxide.
Objectives: After completing this investigation, you should be able to:
• Describe the chemical and physical characteristics of methane hydrate and its distribution
in the Earth environment.
• Demonstrate how methane hydrates could be major sources of atmospheric and oceanic
carbon dioxide.
• Compare possible similarities in the role of methane hydrates in atmospheric and oceanic
carbon dioxide concentrations during PETM and modern climate change.
PETM and Methane Hydrates
The PETM, the abrupt warming of Earth’s atmosphere and ocean and associated environmental
impacts that occurred about 55 million years ago, was global in scale and lasted for
approximately 100,000 years. It was likely triggered by the rapid emission of carbon dioxide
(CO2) or by methane (CH4) which chemically reacts with oxygen to produce CO2 (and
water). Possible sources of the huge amount of carbon that was necessary for producing the
PETM are not known with certainty. It could have been from the release of methane (CH4)
from decomposition of hydrate deposits in seafloor sediments, CO2 from volcanic activity, or
oxidation of organic-rich sediments. There is considerable scientific evidence pointing to the
possibility that the release of methane from naturally occurring solid methane hydrate deposits
in ocean sediments played a prime role in producing the PETM.
Methane hydrate (also called methane clathrate and methane ice) is one of a unique class
of chemical substances composed of molecules of one material forming an open solid crystal
lattice that encloses, without chemical bonding, molecules of another material as represented
in Figure 1. Methane hydrate is a solid form of H2O that contains a large amount of methane
within its crystal structure. It is the inclusion of sufficient methane molecules within the open
cavities between water molecules that causes the stable solid structure to form (i.e., methane
hydrate).
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Figure 1. Methane hydrate is a solid substance in which water molecules form an open
crystalline lattice enclosing, without chemical bonding, molecules of methane.
[National Energy Technology Laboratory, DOE]
For a visualization of the chemical structure of this substance that somewhat resembles ordinary
water ice, go to: http://sag1.chem.pitt.edu/clathrate/. The image to the right shows chunks of
methane hydrate burning. Scroll down to view the representation of numerous water molecules
forming a crystal lattice, or “water cage,” surrounding a single methane molecule. Click on the
“spin” box to animate the view. [The view was created with Jmol: an open-source Java viewer
for chemical structures in 3 dimensions.]
1. In this animation (and in Figure 1), the central molecule represents four hydrogen atoms
bonded to a(n) [(oxygen)(carbon)] atom. The surrounding water molecules form the crystal
lattice that makes the substance solid.
Within certain pressure and temperature ranges, methane hydrates form and remain stable in
the Earth environment. To view methane hydrate formation and outcrops on the seafloor of the
Gulf of Mexico and to answer the following questions, go to: http://2100science.com/Videos/
Frozen_Fuel.aspx. Click on the arrowhead in the middle of the YouTube screen to start the
program.
2. Early in the 8-minute video and again at about 7:40 minutes into the video you can view
the burning of methane hydrate. A scientific error was made in the video narration with
the statement that “methane hydrate is frozen methane.” Evidence that this statement is
probably not true is the [(absence)(presence)] of liquid water that can be seen as the burning
of methane hydrate takes place. The flames seen result from the combustion of CH4. The
loss of CH4 molecules leads to the collapse of the crystal lattices formed by the water
molecules, so solid turns to liquid.
3. According to the narration (described at about 3:55), the actual seafloor observations in this
video were made at a depth of [(1200)(2100)(2900)] feet.
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4. The actual formation of methane hydrate can be seen in the video starting at about 4:50.
The CH4 entering the sampling tube in which the methane hydrate forms is in its [(liquid)
(solid)(gas)] phase.
5. Methane hydrate outcrops can be viewed starting at 6:10. The existence of such outcrops
is strong evidence that methane hydrate is [(stable)(unstable)] at the pressures and
temperatures at that seafloor location.
Figure 2 is a methane hydrate phase diagram showing the combination of temperatures and
pressures (given as water depth in meters). In the diagram “water-ice” refers to ordinary ice.
Enclosed in the yellow area are combinations of temperature and pressure at which (solid)
methane hydrate can stably exist.
Figure 2. Methane Hydrate Phase Diagram denoting depth (i.e., pressure) and temperature
at which methane hydrate can exist. Methane hydrate is a solid. [National Energy
Technology Laboratory, DOE]
6. The solid line between yellow and blue portions of the phase diagram marks the transition
between conditions under which methane hydrate can or cannot exist. It indicates that at
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sufficiently high pressures, methane hydrate can exist at temperatures above the melting
point of ordinary ice. At about 880 m (the depth of the Gulf of Mexico seafloor where the
methane hydrate outcrops were observed in the above video), the temperature could have
been as high as [(+8 °C)(+10 °C)(+12 °C)].
7. The phase diagram also shows that methane hydrate can exist at relatively shallow depths.
At a temperature of 0 °C, methane hydrate could exist at water depths as shallow as about
[(300 m)(400 m)(500 m)].
It should be noted that the Figure 2 phase diagram is based on interactions of pure substances.
In addition to temperature and pressure, the composition of both the water and the gas are
critically important when making predictions of the stability of methane hydrates in different
environments.
Methane Hydrates and the Spring 2010 Gulf of Mexico Deepwater Oil Spill:
In the Deepwater Horizon oil spill catastrophe, methane hydrate was at least implicated as the
possible source of the methane gas that likely caused the explosion and fire that destroyed the
Deepwater Horizon oil drilling platform. In the initial clean-up efforts, it was unquestionably
identified as responsible for thwarting the initial attempt of BP engineers to deploy an oil
containment dome, acting as an upside-down funnel, to capture escaping oil and piping it to a
storage vessel on the surface.
When the oil containment dome was deployed on May 7-8, it failed because the accumulation
of relatively low density methane hydrate crystals formed a slush that made the dome too
buoyant and clogged it up. The Figure 2 phase diagram shows why methane hydrate formed
when methane and water mixed inside the dome. This can be seen by plotting a point on the
phase diagram at a depth of 1500 m and temperature of 5.5 ºC, representing the conditions at
the seafloor well site. The plot falls within the yellow portion of the phased diagram indicating
stable conditions for the existence of methane hydrate.
Methane Hydrates and PETM: Because the temperature and pressure ranges at which
methane hydrates can exist are found throughout much of Earth’s subsurface environment, it
carries with it great potential to impact climate. This was as true in the past as it is now. As
mentioned earlier, there is strong evidence that the release of CH4 from methane hydrates
might have been the primary forcing agent producing the PETM. This possibility has been
thoroughly treated in learning materials developed by the Deep Earth Academy at: http://www.
oceanleadership.org/wp-content/uploads/2009/06/8_petm_abrupt-events.pdf. We recommend
that you examine the materials.
Global Distribution of Methane Hydrates: Figure 3 describes the distribution
of organic carbon in various Earth reservoirs. Gas hydrates are primarily methane hydrates,
although other molecules of similar size to CH4 (including hydrogen sulfide, carbon dioxide,
ethane, and propane) form gas hydrates.
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Figure 3. Earth reservoirs of organic carbon.
[http://marine.usgs.gov/fact-sheets/gas-hydrates/gas-hydrates-3.gif]
8. The one organic carbon reservoir greater than all the other reservoirs combined is
[(the ocean)(fossil fuels)(the land)(atmosphere)(gas hydrates)].
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Summary: Figure 4 summarizes major aspects of methane hydrates in the Earth
environment.
Figure 4. Types of Gas (mostly Methane) Hydrate Deposits. [U.S. National Energy Technology
Laboratory (NETL) [http://204.154.137.14/technologies/oil-gas/FutureSupply/
MethaneHydrates/about-hydrates/geology.htm]
9. Figure 4 shows the two sources of the methane that are incorporated in the methane hydrate
deposits. Biogenic generated gas CH4 is the common by-product of bacterial ingestion of
organic matter. It is considered to be the dominant source of the methane hydrate layers
within shallow sea floor sediments. [(Hydrogenic)(Cryogenic)(Thermogenic)] generated
gas CH4 methane is produced by the combined action of heat, pressure and time on deepburied organic material that also produces petroleum.
While not discussed here, large deposits of methane hydrates occur in permafrost areas of the
Earth. With global warming and associated thawing of vast frozen land areas, the expectation is
that significant quantities of CH4 will be released. Their oxidation will lead to additional CO2,
enhancing the greenhouse effect.
Climate Studies: Investigations Manual 2010-2011
COS 8 - 1
GLOBAL WARMING: RISING SEA
LEVELS AND COASTAL IMPACTS
1. As directed by your instructor, complete this activity with any associated, linked images.
Also print the Weekly Ocean News or Supplemental files as designated. (Check for
additional News updates during the week.)
2. Reference: Chapter 8 in the Ocean Studies textbook. Complete the Investigations in the
Ocean Studies Investigations Manual as directed by your instructor.
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An update on:
Japan’s 2011 Great Tohoku Earthquake/Tsunami Event
On 11 March 2011, Japan experienced its largest earthquake since modern instrumental
recordings began 130 years ago. The earthquake was also the fourth largest in the world
since 1900. It, in turn, triggered the most devastating tsunami in Japan’s history. The
magnitude 9.0 earthquake occurred at 2:46 pm local time (5:46 UTC) at 38.322 degrees N,
142.369 degrees E beneath the Pacific Ocean. Its epicenter was at a depth of 32 km
(19.9 mi) about 130 km (81 mi) east of the City of Sendai off the coast of the northeastern
section (Tohoku) of Japan’s main land mass and largest island, Honshu. In Figure 1, the red
dot shows the map location of the epicenter.
In Figure 1, green to yellow shades depict (land) topographical relief. Japan stretches
diagonally on the map from the upper right to lower left. North is up on the map. The blue
colors report ocean bathymetry with the darkest blue denoting greatest water depths. The
darkest blue places the Japan Trench with depths to 7.25 km (4.5 mi). The broad medium
blue area to the southeast depicts part of the Pacific tectonic plate that is moving about
80 mm/year in the direction of the white arrows relative to the North American plate, which
extends in a lobe shape southwestward from the upper right of the image to about the center
of the view, and the Eurasian plate further west. The earthquake resulted from sudden thrust
faulting on or near the subduction zone interface plate boundary where the Pacific plate is
plowing under the North American plate.
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Figure 1. Bathymetric/topographic map showing location of Tohoku Earthquake
epicenter. [Adapted from NOAA NGDC]
The earthquake movement abruptly displaced huge quantities of water and created an
extremely destructive tsunami with wave heights up to 10 m (33 ft) striking Japan, with some
travelling up to 10 km (6 mi) inland. Many thousands of people were killed or never found.
Additionally, its impact set the stage for one of the most serious nuclear power plant crises to
date. The entire Tohoku event, mostly due to tsunami impacts, is already seen as the costliest
natural disaster ever for Japan.
The earthquake generated water waves that propagated outward in all directions along the
ocean surface, like waves rippling outward along the water surface when a stone is dropped
into a pond. Tsunami waves travel outward until reaching shore, whether near or distant.
They evolve into lower-amplitude waves as they spread out, becoming less damaging.
Because tsunami are shallow water waves that “feel” the ocean bottom, their wave crests
progress along the ocean surface at varying speeds related to changes in the depth of the
underlying water. This can be seen in Figure 2.
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Figure 2. Model generated pattern of the leading wave of the Tohoku Tsunami.
[NOAA Center for Tsunami Research, PMEL]
1. The color coding in Figure 2 shows that the darker the color, the higher the tsunami wave
height. Near the earthquake epicenter, maximum wave heights were near
[(2)(4)(6)(8)] feet. At these locations, the wave energy was also the greatest, with the
potential for causing the greatest damage.
2. The white dashed lines show the position of the leading wave after intervals of time.
Note the “6 hours” line. It shows that in some places the wave must have been moving
forward faster than in other places. The color coding shows [(higher)(lower)] wave
heights are generally associated with slower wave speeds.
3. Shallow water wave speeds decrease as the water depth decreases, and their wave heights
increase. Note the kink in the “6 Hours” line to the northwest of Hawaii. It shows that
compared to the “6 hours” line to either side, the wave speed at the kink must be slower,
the wave heights must be higher, and the water depth must be [(deeper)(shallower)].
You can confirm this by referring to a bathymetric chart of the region.
The differing depths of the ocean often influence the direction of movement of the advancing
wave, as well as impacting the magnitude of its wave energy. Note the kink in the “9 hours”
line where it approaches the west coast of the U.S. The color coding shows that the greatest
impact of the Tohoku Tsunami on the U.S. mainland was probably in Northern California or
Oregon. Indeed, tidal gages revealed that Crescent City, CA experienced impact.
Figure 3 shows changes in the actual observed water levels (in red) versus predicted tide
levels (in blue). The green curve depicts departure from the predicted water level. The graph
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shows that for nearly the first two-thirds of 11 March 2011, the observed water levels were
very close to the predicted tide values.
Figure 3. Crescent City, CA tide data showing arrival and impact of Tohoku Tsunami.
4. It took a little more than 9 hours following the Tohoku earthquake for the leading wave
of the resulting tsunami to travel across the Pacific and arrive at Crescent City a few
minutes before 1600 GMT on 11 March 2011. According to the green (Observed –
Predicted) curve, the initial observed tsunami water rise was about [(1.5)(2.5)(5.0)] feet
above the predicted water level.
5. A short time later, the water level dropped to [(2.0)(2.5)(6.0)] feet below the predicted
water level. A couple of hours later, the water level reached a height more than 7 feet
above predicted water level. The graph shows that after the tsunami initially arrived
there were numerous alternating high and low water level departures compared to the
predicted tide levels.
6. The alternating pattern of water level fluctuations beyond predicted levels indicate the
tsunami is a [(single)(multiple)] wave event.
Our purpose here has been to explore some of the scientific underpinnings of the Tohoku
Earthquake/Tsunami, including its impact on the U.S. West Coast. Obviously, the full story
of the event will not be told for decades.
Rising Sea Levels and Coastal Impacts:
The International Panel on Climate Change (IPCC), in its Fourth Assessment entitled
Climate Change 2007 (http://www.ipcc.ch/), states that “warming of the climate system is
unequivocal, as is now evident from observations of increases in global average air and
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ocean temperatures, widespread melting of snow and ice and rising global average sea level.”
[p. 2, Summary for Policymakers] The rise in sea level is already being felt and increasingly
will be felt in coastal environments worldwide in the decades ahead.
There is very strong evidence that global sea level gradually rose in the 20th century and is
currently rising. Figure 4 displays sea level based on coastal tide-gauge data (blue line) from
1870 through 2009 and based on satellite altimeter data (red line) from 1993 through 2009.
The light blue displays the estimated error range in the data.
Figure 4. Estimated changes in global mean sea level, 1870 - 2009.
[© Copyright CSIRO Australia, 25 June 2010]
7. Over the period of record of tide-gauge data shown in Figure 4, the global mean sea level
increased nearly [(50)(100)(175)(250)] mm. This is equivalent to 9.8 in.
8. Figure 4 indicates that since 1993, global mean sea level values determined by coastal
tide gauges and by satellite altimetry were [(identical)(in close agreement)
(showed differences exceeding 50 mm)].
9. Compare the slopes of the blue and red sea-level curves during the 1990-1999 decade
with their inclinations during the 2000-2010 decade. The comparison shows a more rapid
change in sea level during the [(1990-1999)(2000-2009)] decade.
Figure 5 from the IPCC Fourth Assessment shows the global mean sea level in terms of
deviation from the 1980-1999 mean in the past and as projected into the future. Note that
Figures 1 and 2 both display essentially the same instrument-based sea level change data
during the time period from 1870 through 1999, although the time periods used in their
determinations of the mean from which sea level change is measured are different.
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Figure 5. Past and projected global mean sea level change measured as
departure from the 1980-1999 mean. [IPCC AR4]
10. In Figure 5, the red line is a reconstruction of global mean sea level from tide gauges,
with the light red shading denoting the estimated error range in the data. They show the
instrumental record of mean sea level extending from [(1800)(1840)(1870)] to nearly the
present. The green line superimposed on the red line in the several years before 1999
shows global average sea level as measured from satellite altimetry.
The blue shading to the right in Figure 5 shows the range of model projections to the
Year 2100. These models predict a rise of sea level between about 220 and 500 mm (8.7 and
19.7 in) above the 1980-1999 mean. The models relied on by the IPCC assessment to
produce these projections did not include the possible impact of accelerated melting of land
ice, as it was determined that melting projections could not be made with confidence.
However, it was noted that dramatic increases in the rates of melting of land ice and the
consequent sudden rises in global mean sea level could have catastrophic consequences.
11. Especially vulnerable to the impacts of rising sea level are the large numbers of people
living in low-lying coastal areas (e.g., Pacific islands, The Netherlands, southern
Louisiana, Florida). According to a June 2007 United Nations Environment Programme
(UNEP) study and shown in Figure 6, a global total of approximately
[(13)(110)(145)] million people live where the population would be especially vulnerable
to a sea-level rise of one meter.
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Figure 6. Population, area and economy affected by a 1 m sea level rise. [Anthoff, D.,
Nicholls, R.J., Tol, R.S.J. and Vafeidis. A.T. (2006). Global and regional exposure
to large rises in sea-level: a sensitivity analysis. Working Paper 96. Tyndall
Centre for Climate Change Research, Norwich. Cartographer/Designer -Hugo
Ahlenius, UNEP/Grid-Arendal]
It can be seen in Figure 6 that the greatest number of people who are vulnerable to sea-level
rise live in Asia, but the impact is worldwide. Especially vulnerable are those living in
densely populated river megadeltas. It is almost certain that the more than one million
people living in the Ganges-Brahmaputra, Mekong, and Nile deltas will be impacted if
current rates of sea-level rise continue to mid-century and there is no adaptation.
Sea-Level Rise Impacts:
Sea-level rise has numerous impacts. The total area of coastal wetlands will diminish. Most
coastal wetlands are found on very low gradient coasts dominated by large deltas. Loss of
coastal wetlands threatens marine diversity and fisheries production, reduces natural
pollution- and flood-control mechanisms, and makes the coastal zone more vulnerable to
storm surges. It should be noted that the problems associated with rising global sea level are
made more severe in many areas because of land subsidence and coastal erosion. The U.S.
Mississippi delta is diminishing in area as much as 100 km2 per year (largely due to human
activity), placing New Orleans at an ever greater risk for flooding.
One coastal nation that is actively preparing for rising sea levels is The Netherlands, which
has dealt with coastal and river flooding for centuries. Nearly two-thirds of the country
already lies below sea level. One city is located 7 m (23 ft) below sea level. An expansive
system of dams, dikes, and dunes are included in the country’s flood protection system.
Floods have been a fact of life in western Netherlands; a devastating flood in January 1953 in
which 1835 people were drowned led to the creation of The Netherlands Delta Project in
1959.
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12. To learn more about The Netherlands Delta Project, go to:
http://www.deltawerken.com/Deltaworks/23.html. The Delta Plan focused on the
southeastern delta area of the country generally in the densely populated regions near the
mouths of the Meuse, Schelde, and [(Elbe)(Danube)(Rhine)] Rivers. These rivers
formed the largest delta in northwest Europe.
While at the Deltaworks website, visit some of the barriers and dams built as part of the Delta
Project. Start by clicking on “The Oosterschelde storm surge barrier” to the left. After
reading about the storm surge barrier, click on the “Video” image and view the video
program. After the viewing, look around the Deltaworks website to better understand the
comprehensive Dutch approach to mitigating the impacts of floods. A visit to the Maeslant
barrier located near Rotterdam is recommended as the barrier design typifies the creative
thinking that has gone into Dutch flood control.
The Dutch consider that dealing with climate change is basically an issue of national
security, but it also deals with life and work, agriculture, ecology, recreation and leisure,
landscape, infrastructure and energy. The U.S. and other countries with significant deltas
and coastal wetlands are facing similar issues that must be addressed sooner or later.
Unquestionably, the coastal zone is a particularly dynamic and vulnerable portion of the
Earth system.
Summary:
The average worldwide sea level has been rising over the past century and it currently
appears to be rising at an accelerating rate. Practically all climate change projections indicate
significant rises that will submerge low-lying islands and vast coastal areas, increase
frequency and intensity of catastrophic coastal flooding, and displace hundreds of millions of
people around the globe. It is of great urgency that mitigation and adaptation efforts be
developed and implemented regarding this growing threat.
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If directed by your instructor, place the answers to Investigations 8A and 8B on the
Investigations Answer Forms and this Current Ocean Studies on the Current Ocean
Studies Answer Form linked from the AMS Ocean Studies website.
©Copyright 2011, American Meteorological Society