Transcript Methane

Geobiology
Methane Hydrates and Associated Seeps
Formation and Occurrence
Seep Ecology
Biogeochemistry
Possible Role in Climate-Related Extinctions
Readings: Berner PNAS 99, 4172-4177, 2002
Dickens Org.Geochem. 32, 1179, 2001
Katz et al Science 286, 1531, 1999
Jahnke et al AEM 61, 576, 1995
Acknowledgements:
S. Goffredi and V. Orphan, MBARI
T. Hoehler, NASA AMES
Linda Jahnke, NASA AMES
USGS
A gas hydrate is a crystalline solid; its building blocks consist of a gas molecule surrounded by a
cage of water molecules. This it is similar to ice, except that the crystalline structure is stabilized
by the guest gas molecule within the cage of water molecule. Many gases have molecule sizes
sulfide, and several low-carbon-number hydrocarbons, but most marine gas hydrates that have
been analyzed are methane hydrates.
Crest of Blake Ridge
hydrate occursin
the sediment from
this reflection to
the seafloor
BSR
Reflections are weeker
due to cementation by
gas hydrate
Blanking
Sea Floor
Reflections from
dipping strata
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methane
• End product of organic matter fermentation
– methanogensis  biogenic gas
CO2 + 4H2  CH4 + 2H2O
CO2 reduction
methanogenesis
CH3COOH  CH4 + CO2 acetoclastic
(CH3)3N + 3H2  3CH4 + NH3
methylotrophic methanogensis
•
End-stage product of organic matter burial. At burial
temperatures of 200°C plus coal, kerogen and hydrocarbons
decompose to yield (eventually) methane and graphite
– catagenesis  thermogenic gas
•
Came with formation of the planet (Thomas Gold)
Methanogenesis vs Sulfate Reduction
CO2 + 4H2  CH4 + 2H2O
CO2 reduction by MPA
(methane producing archaea)
SO42- + 4H2  S2- + 4H2O
sulfate reduction by SRB
(sulfate reducing bacteria)
Methanogenesis vs Sulfate Reduction
or
CO2 + 4H2  CH4 + 2H2O
CO2 reduction by MPA
(methane producing archaea)
SO42- + 4H2  S2- + 4H2O
sulfate reduction by SRB
(sulfate reducing bacteria)
Where [ ] denotes concentration; y is an activity coefficient;
P denotes partial pressure; R is the universal gas constant;
T is absolute temperature; and G0(T)-SR and G0(T)-MP
are the standard free energies of reaction for sulfate reduction and methane production, corrected to ambient tem-
Acknowledgement: T. Hoehler, FEMS Microbial Ecology 38, 33, 2001
Methane
• Biogenic gas has a diagnostic d13C= – 40 to -100‰
signature
Ubiquitous and abundant in subsurface sediments, rice
paddies, arctic tundra, animal guts (cows to termites)
• Thermogenic gas has a d13C = – 20 to -40‰
• Short residence time in ocean and atmosphere where it
is consumed (methanotrophy) by bacteria
(methanotrophs)
• Methanotrophs can use O2 (aerobic methanotrophy)
•
or SO4 (anaerobic methanotrophy = reverse
methanogenesis)
• Methane is a significant greenhouse gas and has
(recently) been implicated in many geobiological issues
Methan
e
Gas Hydrate Stability Curve
To the left is a curve representing the stability of Gas Hydrate in sea
water. Pressure and temperature are two of the major factors controlling
where the hydrate (solid) or methane gas will be stable. Whether or not
gas hydrate actually forms depends on the amount og gas available.
http://woodshole.er.usgs.gov/projectpages/hydrates/what.html
Methane
SEA SURFACE
TEMPERATURE
PHASE BOUNDARY
Gas Hydrate Stability in Ocean
Sediments
SEA FLOOR
The diagram to the right shows where the
same stability curve above crosses the
Temperatures of ocean sedments.
TEMPERATURE (0C)
SEDIMENTS
GAS HYDRATE PRESENT
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Hydrate seams in mud
Hydrate outcropping
on seafloor and
colonised by
chemosynthetic
ecosystem
Methane actively dissociating from a hydrate mound
Methane
Capacity to Trap Gas
Hydrate forms as cement in the pore spaces of sediment as well as in layers and nodules of pure hydrate. Hydrates also
seem to have the capacity to fill sediment pore space and reduce permeability, so that hydrate-cemented sediments act as
seals for gas traps.
Gas Hydrates are stable at the temperatures and pressures that occur in ocean-floor sediments at water depths grater
Than about 500m, and at these pressures they are stable at temperatures above those for ice stability. Gas hydrates also
are stable association with permafrost in the polar regions, both in offshore and onshore sediments. Gas hydrates bind
immense amounts of methane in sea-floor sediments. Hydrate is a gas concentrator, the breakdown of a unit volume of
methane hydrate at a pressure of one atmosphere produces about 160 unit volumes of gas. The worldwide amount of
methane in gas hydrates is considered to contain at least 1x104 gigatons of carbon in a very conservative estimate). This
is about twice the amount of carbon held in all fossil fuels on earth.
Gas hydrate concentration occurs at depocenters, probably because most gas in hydrate is from biogenic methane, and
therefore it is concentrated where there is a rapid accumulation of organic detritus (from which bacteria generate methane)
and also where there is a rapid accumulation of sediments (which protect detritus from oxidation).
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methan
e Where is it found?
Gas Hydrate:
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methan
e
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methane
Ocean 983
(includes dissolved
Organics, and biota)
Atmosphere 3.6
Land 2790
(includes soil,
biota, peat,
and detritus)
Fossil
Fuels
5,000
Gas
hydrates
10,000
Distribution of organic carbon in Earth reservoirs (excluding dispersed carbon in rocks
and sediments, which equals nearly 1,000 times this total amount). Numbers in gigatons
(1015 tons) of carbon.
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methane – Blake Ridge
There is a lot of it out there and all published figures are
only estimates
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methane –
Cascadia Margin
Locations of methane hydrate off the Cascadia Margin
Schematic representation showing the movement of methane and fluids
through an accretionary wedge.
Courtesy of Natural Resource Canada and Dr. Roy Hyndman.
http://www.netl.doe.gov/scng/hydrate/
Ice Worm
Tubeworms
GOM hydrates derived from
thermogenic methane. They
are isotopically distinct and
impregnated with oil
Methan
Does loss of gas from gas hydrate account for extensive ship-sinkings in the
“Bermuda Triangle”? Pleasee
let me pose and answer a serious of questions.
1.
Are there large amount of gas hydrate in the sea floor sediments on the continental rise off the southeastem United
States (western past of “Bermuda Triangle”?)
Yes, I think that our interpretations and mapping shove that.
2.
Did sea floor sedimentary deposits collapse because hydrate processes and cause landslides and release of gas
by eruptions?
Probably, yes.
3.
Could gas release cause a ship to sink?
Absolutely. If you release enough gas you generate a foam having such low density that ship would not be
able to displace enough to float.
4.
Did gas release related to hydrate break down result in sinking of ships off the southeastern United States?
No, I don’t think so. Evidence suggests that the collapse and abrupt release of gas related to hydrate
breakdown probably occurred at the end of the glacial episode when ocean water was tied up in great
continental ice sheets and, thus, sea level was lowered. The lower sealevel caused the pressure on the gas
hydrate at the sea floor to be reduced, which would cause hydrate breakdown and gas release. This
happened about 15,000 years ago or more, when the more technically advanced men’s ships where probably
nothing more than hollow logs.
http://woodshole.er.usgs.gov/project-pages/hydrates/what.html
Methane
Mechanism for sea-level drop to destabilize hydrate
http://marine.usgs.gov/fact-sheets/gas-hydrates
Methane
Mechanism for
sea-level rise to
destabilize
hydrate
http://marine.usgs.gov/fact-sheets/gas-hydrates
Sediment Core from a methane-rich Monterey cold seep
This is a chemistry “profile” from the core
Depth into the sediment (cm)
Methane (µM)
Bacteria feed on
methane and sulfate
Sulfate (mM)
See How
Methane (µM
Depth into the sediment (cm)
As Sulfate (SO4) is
consumed by
bacteria,
Hydrogen Sulfide
(H2S)
is produced
Sulfate (mM)
How do bacteria influence the physical
and chemical environment at seep sites?
CHEMOSYNTHETIC CLAM
COMMUNITIES
SO4
SULFATE
SEAWATER
SEDIMENT
As energy-rich seawater sulfate diffuses
into sediments, it is consumed by
anaerobic bacteria along with methane
Methane-oxidizing &
Sulfate Reducing Bacteria
CH4
METHANE
How do bacteria influence the physical
and chemical environment at seep sites?
SO4
SULFATE
CHEMOSYNTHETIC CLAM
COMMUNITIES
SEAWATER
SEDIMENT
Methane-oxidizing &
Sulfate Reducing Bacteria
CH4
METHANE
As CH4 and SO4 are
consumed, large
amounts of hydrogen
sulfide and carbon
dioxide are produced
How do bacteria influence the physical
and chemical environment at seep sites?
SO4
SULFATE
CHEMOSYNTHETIC CLAM
COMMUNITIES
SEAWATER
SEDIMENT
Methane-oxidizing &
Sulfate Reducing Bacteria
CH4
METHANE
As CH4 and SO4 are
consumed, large
amounts of hydrogen
sulfide and carbon
dioxide are produced
How do bacteria influence the physical
and chemical environment at seep sites?
SO4
SULFATE
SEAWATER
SEDIMENT
Methane-oxidizing &
Sulfate Reducing Bacteria
CH4
METHANE
CLAM SYMBIONTS CAN THEN
USE THE SULFIDE
PRODUCED BY THE
BACTERIA
(plus oxygen) TO LIVE
How do other organisms take advantage of
bacterially produced sulfide?...
It’s called “chemosynthesis”
The process in which carbohydrates are manufactured from carbon
dioxide and water using chemical nutrients as the energy source,
rather than the sunlight used for energy in photosynthesis.
During Photosynthesis green plants produce organic carbon compounds from carbon
dioxide and water, using sunlight as energy. These
compounds can then enter the food chain.
During Chemosynthesis - hydrogen sulfide
is the energy source and it is either taken
up by free-living bacteria or absorbed by
the host invertebrates, and transported to
the symbionts. The bacteria use the energy
from sulfide to fuel the same cycle that plants
use, again resulting in organic carbon compounds
Q. What is the dominant C-assimilation pathway in autotrophy
-photoautotrophy or chemoautotrophy
These clams and worms don’t have
stomachs or mouths!! …How do they
survive?
It’s called “symbiosis”
Living together of organisms of different species.
The term usually applies to a dependent relationship
that is beneficial to both members (also called mutualism).
Symbiosis may occur between plants, animals and/or bacteria
Once inside, the bacteria and animal host
become partners. The bacteria multiply
within the host, eventually integrating
completely.
The animal benefits from food produced by
the bacteria and the symbiont benefits from
the shelter and stable environment
provided by the host.
Seep clams are no ordinary clams!!
Ordinary
clam
Clam chowder
- yum -
Seep clams are no ordinary clams!!
Ordinary
clam
Clam chowder
- yum -
Extraordinary
clam
Rotten eggs
- yuck -
Adductor muscles
Mantle
Gills (symbionts)
Siphon
s
Foo
t
Unlike other animals, these
clams must take up carbon
dioxide (through their enlarged
gills) and sulfide (through their
foot) in order meet the needs
of their symbionts.
carbon
dioxid
e
oxyge
n
bacterial
symbionts
wate
r
sedimen
t
sulfid
e
In addition to strictly ‘seep’ animals, a variety of other
animals benefit from foraging within seep sites.
These include….
Sea urchins
Crabs
Sea cucumbers
Brittle stars
King crabs
Question
• What environmental parameters appear
to be important for establishing the
kinds of bacterial and bacterialinvertebrate communities in Monterey
Bay?
Methane-Dependent
Communities in the GOM
Methane hydrates like this one, which is 540 meters deep in the Gulf of
Mexico, are crystal structures of methane and water which can form under
conditions of low temperature and high pressure. This hydrate mound,
which is over 6 feet in diameter, has risen off of the seafloor because the
"methane ice" is lighter than the sediment or sea water. Click on the
hydrate for a closer look at the inhabitants of the mound
Methane-Dependent
Communities in the GOM
• What environmental parameters
distinguish bacterial and bacterialinvertebrate communities in the Gulf of
Mexico?
Methane-Dependent Communities in GOM
On close inspection, myriads of one to two inch long polychaete
worms can be seen living on and in the surface of the hydrate. These
worms where only discovered on July 15th 1997, and we are just
Beginning to study them. We speculate that they may colonize the
hydrates even when they are buried, and that the worm’s nutrition is
tightly tied to the hydrate itself. However, these and many other
speculations about this new species of worm remain to be tested and
verified.
Methane-Dependent Communities in GOM
Identification of Methanotrophic Lipid Biomarkers in Cold-Seep
Mussel Gills: Chemical and Isotopic Analysis
LINDA L JAHNKE,1* ROGER E. SUMMONS,1 LESLEY M. DOWLING,2
AND
KAREN D. ZAHIRALIS1,3
National Aeronautics and Space Administration, Ames Research Center, Moffett Field, California 94035-10001;
Australian Geological Survey Organisation, Canberra, ACT 2601, Australia2; and
SETT Institute, Mountain View, California 940433
Received 15 August 1994/Accepted 24 November 1994
A lipid analysis of the tissues of a cold-seep mytilid mussel collected from the Louisiana slope of the Gulf
of Mexico was used in conjunction with a compound-specific isotope analysis to demonstrate the presence of
methanotrophic symbionts in the mussel gill tissue and to demonstrate the host’s dependence on bacterially
synthesized metabolic intermediates. The gill tissue contained large amounts of group-specific methanotrophic
biomarkers, bacteriohopanoids, 4-methylsterols, lipopolysaccharide-associated hydrate fatty acids, and type
I-specific 16:1 fatty acid isomers with bond positions at 8, 10, and 11. Only small amounts of these
compounds were detected in the mantle or other tissues of the host animal. A variety of cholesterol and
4-methylsterol isomers were identified as both free and steryl esters, and the sterol double bond positions
suggested that the major bacterially derived gill sterol [11.0% 4α-methyl-cholesta-8(14),24-dien-3β-ol] was
converted to host cholesterol (64.2% of the gill sterol was cholest-5-3β-ol]. The stable carbon isotope values
for gill and mantle preparations were, respectively, -59.0 and - 60.4‰ for total tissue, - 60.6 and – 62.4‰ for
total lipids, - 60.2 and 63.9 ‰ for phospholipid fatty acids, and -71.8 and - 73.8 ‰ for sterols. These stable
carbon isotope values revealed that the relative fractionation pattern was similar to the patterns obtained in
Geochim. Cosmochim. Acta 58:2853-2863, 1994) further supporting the conversion of the bacterial methylsterol pool.
Methane-Dependent Communities in GOM
a
TABLE 1. Carbon isotopic compositions of seep mussel tissues
Gill tissue
Mantle tissue
Remains
Component
Total lipid
Cell residue
Total tissue
a Total
lipid was extracted and nonlipid cell residue was recovered as described
in Materials and Methods. Carbon isotope compositions are reported as δ13C
values, which were calculated as follows: δ13C = [(Rsample - Rstandard)/ Rstandard]
103, where Rsample is the 13C/12C ratio of the sample and 1 Rstandard is the
13C/12C ratio of Peedee belemnite.
Per Cent Fatty Acid Composition
Methane-Dependent Communities in GOM
Mussel Gill
Mussel Mantle
Methylococcus capsulatus
Identification of Type I Methanotrophic Signature
Fatty Acids in Mussel Gill Tissue
Methane-Dependent Communities in GOM
d13C GOM CH4 ~ -45‰
d type 1 RUMP oxidation and assimilation of CH4~16 ‰
Calculated d13C biomass = -61 ‰ (Found = - 58 ‰)
d biosynthesis of polyisoprenpoid lipids ~10 ‰
Calculated d13C sterol & hopanol = -68 ‰
Following the Flow of Carbon Compounds in
Methane-Dependent Communities in GOM
Calculated
symbiont
symbiont
host
-68 ‰
Found
-70.7 ‰
-68 ‰
-67.3 to -74.1‰
-68 ‰
-69.8‰
Sulfide-Dependent Communities in GOM
In the Gulf of Mexico enough sulfide comes out of the sediment to reach the
gill-like plumes of the young tubeworms (which stick out of the top of their
tubes) as shown in the lower left panel. Our current studies indicate that the
adult tubeworms in large ”bushes” may take up the sulfide from the
sediment using the root-like end of their tubes, as shown in the upper right
panel.
Sulfide-Dependent Communities in GOM
The Gulf of Mexico cold-seep tube worms can get up to 10
feet long and sometimes live in groups of millions of
individuals. The animals in this picture are about 6 feet long
and as big around as your finger. Click on the worms for a
closer view.
The new white tube growth can be seen above the previously
stained tubes. In one year these worms grow less than one
inch. After several years of measurements, we have calculated
that the large worms are over 100 years old.