geobiology methane hydrates and associated seeps formation and occurrence seep ecology

GeobiologyMethane Hydrates and Associated Seeps

Formation and Occurrence Seep Ecology

Biogeochemistry

Possible Role in Climate-Related ExtinctionsReadings: Berner PNAS 99, 4172-4177, 2002

Dickens Org.Geochem. 32, 1179, 2001Katz 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

http://woodshole.er.usgs.gov/project-pages/hydrates/

what.html

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 occursinthe sediment fromthis reflection tothe seafloor

Reflections are weekerdue to cementation bygas hydrate

BSR Blanking Sea FloorReflections fromdipping strata

Methane• End product of organic matter fermentation

– methanogensis ‡ biogenic gas

CO2 + 4H2 ‡ CH4 + 2H2O

CO2 reduction CH3COOH ‡ CH4 + CO2 acetoclastic methanogenesis

(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 + 2H2OCO2 reduction by MPA

(methane producing archaea)

SO42- + 4H2 ‡ S2- + 4H2O

sulfate reduction by SRB(sulfate reducing bacteria)

Methanogenesis vs Sulfate Reduction

CO2 + 4H2 ‡ CH4 + 2H2OCO2 reduction by MPA

(methane producing archaea)

SO42- + 4H2 ‡ S2- + 4H2O

sulfate reduction by SRB(sulfate reducing bacteria)

Acknowledgement: T. Hoehler, FEMS Microbial Ecology 38, 33, 2001

or

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 reduc-tion and methane production, corrected to ambient tem-

Methane• Biogenic gas has a diagnostic 13C= – 40 to -100‰ signature

Ubiquitous and abundant in subsurface sediments, rice paddies, arctic tundra, animal guts (cows to termites)

• Thermogenic gas has a 13C = – 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

Methane

http://woodshole.er.usgs.gov/project- pages/hydrates/what.html

Gas Hydrate Stability Curve

To the left is a curve representing the stability of Gas Hydrate in seawater. Pressure and temperature are two of the major factors controllingwhere the hydrate (solid) or methane gas will be stable. Whether or notgas hydrate actually forms depends on the amount og gas available.

Methane

Gas Hydrate Stability in OceanSediments

The diagram to the right shows where the same stability curve above crosses theTemperatures of ocean sedments.

TEMPERATURE (0C)

http://woodshole.er.usgs.gov/project-pages/hydrates/what.html

SEDIMENTS GAS HYDRATE PRESENT

TEMPERATURESEA SURFACE

PHASE BOUNDARY

SEA FLOOR

Hydrate seams in mud

Hydrate outcropping on seafloor and colonised by chemosynthetic eco

system

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 alsoseem to have the capacity to fill sediment pore space and reduce permeability, so that hydrate-cemented sediments act asseals for gas traps.

Gas Hydrates are stable at the temperatures and pressures that occur in ocean-floor sediments at water depths graterThan about 500m, and at these pressures they are stable at temperatures above those for ice stability. Gas hydrates alsoare stable association with permafrost in the polar regions, both in offshore and onshore sediments. Gas hydrates bindimmense amounts of methane in sea-floor sediments. Hydrate is a gas concentrator, the breakdown of a unit volume ofmethane hydrate at a pressure of one atmosphere produces about 160 unit volumes of gas. The worldwide amount ofmethane in gas hydrates is considered to contain at least 1x104 gigatons of carbon in a very conservative estimate). Thisis 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, andtherefore 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).

Methane


Gas Hydrate: Where is it found?

Methane


Methane


Ocean 983(includes dissolvedOrganics, and biota)

Land 2790(includes soil,

biota, peat,and detritus)

Atmosphere 3.6

FossilFuels5,000

Gas hydrates10,000

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.

Methane – Blake RidgeThere is a lot of it out there and all published figures are

only estimates


http://www.netl.doe.gov/scng/hydrate/

Methane – Cascadia Margin

Locations of methane hydrate off the Cascadia Margin

Schematic representation showing the movement of methane and fluidsthrough an accretionary wedge.

Courtesy of Natural Resource Canada and Dr. Roy Hyndman.

GOM hydrates derived from thermogenic methane. They are isotopically distinct an

d impregnated with oil

Ice Worm

Tubeworms

Methane


Does loss of gas from gas hydrate account for extensive ship-sinkings in the“Bermuda Triangle”? Please 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.

MethaneMechanism for sea-level drop to destabilize hydrate

http://marine.usgs.gov/fact-sheets/gas-hydrates

Methane Mechanism for sea-level rise to destabilize hydr

ate

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

Methane (µM)

Sulfate (mM)

Dep

th in

to t

he

sed

imen

t (c

m)

Bacteria feed onmethane and sulfate

As Sulfate (SO4) is consumed by

bacteria, Hydrogen Sulfide

(H2S) is produced

See How

Methane (µM

Sulfate (mM)

Dep

th in

to t

he

sed

imen

t (c

m)

How do bacteria influence the physical and chemical environment at seep sites?

SO4

SULFATE

CHEMOSYNTHETIC CLAM COMMUNITIES

SEDIMENT

CH4

METHANE

Methane-oxidizing & Sulfate Reducing Bacteria

As energy-rich seawater sulfate diffuses into sediments, it is consumed by

anaerobic bacteria along with methane

SEAWATER


SO4

SULFATE


CH4

METHANE


As CH4 and SO4 are consumed, large

amounts of hydrogen sulfide and carbon

dioxide are produced

SEAWATER

SEDIMENT


SO4

SULFATE


CH4METHANE


As CH4 and SO4 are consumed, large

amounts of hydrogen sulfide and carbon

dioxide are produced

SEAWATER

SEDIMENT

H2S

HYDROGEN SULFIDE


SO4

SULFATE

CH4METHANE


SEAWATER

SEDIMENT

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. Thesecompounds 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 tothe symbionts. The bacteria use the energy from sulfide to fuel the same cycle that plantsuse, again resulting in organic carbon compoundsQ. 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”

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.

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

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)

Siphons

Foot

Unlike other animals, theseclams must take up carbondioxide (through their enlarged gills) and sulfide (through their foot) in order meet the needsof their symbionts.

carbon dioxide

water

oxygen

sediment

sulfide

bacterial symbionts

In addition to strictly ‘seep’ animals, a variety of other animals benefit from foraging within seep sites.

These include….

CrabsSea urchins

Sea cucumbers

Brittle starsKing crabs

Question

• What environmental parameters appear to be important for establishing the kinds of bacterial and bacterial- invertebrate communities in Monterey Bay?

Methane-DependentCommunities 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-DependentCommunities in the GOM

• What environmental parameters distinguish bacterial and bacterial- invertebrate communities in the Gulf of Mexico?

Methane-Dependent Communities in GOMOn 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 GOMIdentification of Methanotrophic Lipid Biomarkers in Cold-Seep

Mussel Gills: Chemical and Isotopic AnalysisLINDA 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 94035-1000 1;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 Gulfof Mexico was used in conjunction with a compound-specific isotope analysis to demonstrate the presence ofmethanotrophic symbionts in the mussel gill tissue and to demonstrate the host’s dependence on bacteriallysynthesized metabolic intermediates. The gill tissue contained large amounts of group-specific methanotrophicbiomarkers, bacteriohopanoids, 4-methylsterols, lipopolysaccharide-associated hydrate fatty acids, and typeI-specific 16:1 fatty acid isomers with bond positions at 8, 10, and 11. Only small amounts of thesecompounds were detected in the mantle or other tissues of the host animal. A variety of cholesterol and4-methylsterol isomers were identified as both free and steryl esters, and the sterol double bond positionssuggested that the major bacterially derived gill sterol [11.0% 4α-methyl-cholesta-8(14),24-dien-3β-ol] wasconverted to host cholesterol (64.2% of the gill sterol was cholest-5-3β-ol]. The stable carbon isotope valuesfor gill and mantle preparations were, respectively, -59.0 and - 60.4‰ for total tissue, - 60.6 and – 62.4‰ fortotal lipids, - 60.2 and 63.9 ‰ for phospholipid fatty acids, and -71.8 and - 73.8 ‰ for sterols. These stablecarbon isotope values revealed that the relative fractionation pattern was similar to the patterns obtained inGeochim. Cosmochim. Acta 58:2853-2863, 1994) further supporting the conversion of the bacterial methyl-sterol pool.

Methane-Dependent Communities in GOM

a Total lipid was extracted and nonlipid cell residue was recovered as describedin Materials and Methods. Carbon isotope compositions are reported as δ13Cvalues, 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.

TABLE 1. Carbon isotopic compositions of seep mussel tissuesa

Component

Total lipid

Cell residue

Total tissue

Gill tissue Mantle tissue Remains


Mussel Gill

Mussel Mantle

Identification of Type I Methanotrophic SignatureFatty Acids in Mussel Gill Tissue

Methylococcus capsulatus

Per

Cen

t F

atty

Aci

d C

om

po

siti

on


13C GOM CH4 ~ -45‰

type 1 RUMP oxidation and assimilation of CH4~16 ‰

Calculated 13C biomass = -61 ‰ (Found = - 58 ‰)

biosynthesis of polyisoprenpoid lipids ~10 ‰

Calculated 13C sterol & hopanol = -68 ‰

Following the Flow of Carbon Compounds in


symbiontCalculated Found

-68 ‰ -70.7 ‰

symbiont-68 ‰ -67.3 to -74.1‰

host -68 ‰ -69.8‰

Sulfide-Dependent Communities in GOMIn the Gulf of Mexico enough sulfide comes out of the sediment to reach thegill-like plumes of the young tubeworms (which stick out of the top of theirtubes) as shown in the lower left panel. Our current studies indicate that the adult tubeworms in large ”bushes” may take up the sulfide from thesediment using the root-like end of their tubes, as shown in the upper rightpanel.

Sulfide-Dependent Communities in GOM

The Gulf of Mexico cold-seep tube worms can get up to 10feet long and sometimes live in groups of millions ofindividuals. The animals in this picture are about 6 feet longand as big around as your finger. Click on the worms for acloser view.

The new white tube growth can be seen above the previouslystained tubes. In one year these worms grow less than one inch. After several years of measurements, we have calculatedthat the large worms are over 100 years old.

geobiology methane hydrates and associated seeps formation and occurrence seep ecology

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