Geobiology Methane Hydrates and Associated Seeps Formation and Occurrence Seep Ecology

1. 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

2. 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 Reflections are weeker due to cementation by gas hydrate Blanking BSR Sea Floor Reflections from dipping strata http://woodshole.er.usgs.gov/project-pages/hydrates/what.html

3. Methane • •Endproductoforganicmatterfermentation • –methanogensis‡ biogenic gas • CO2+4H2‡ CH4 + 2H2O • CO2 reductionCH3COOH‡ CH4 + CO2acetoclasticmethanogenesis • (CH3)3N + 3H2‡3CH4 + NH3 • methylotrophic methanogensis • • End-stageproductoforganicmatterburial.Atburial • temperatures of200°Cpluscoal,kerogenandhydrocarbons • decomposetoyield(eventually)methaneandgraphite • –catagenesis‡thermogenicgas • Camewithformationoftheplanet(ThomasGold)

4. MethanogenesisvsSulfate Reduction • CO2+4H2‡ CH4+2H2O • CO2 reduction by MPA • (methane producing archaea) SO42-+4H2‡ S2-+4H2O • sulfate reduction by SRB • (sulfate reducing bacteria)

5. MethanogenesisvsSulfate Reduction or • CO2 + 4H2‡ CH4 + 2H2O • CO2 reduction by MPA • (methane producing archaea) 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- SO42-+ 4H2‡ S2-+ 4H2O sulfatereductionbySRB (sulfate reducing bacteria) Acknowledgement: T. Hoehler, FEMS Microbial Ecology 38, 33, 2001

6. Methane • •Biogenicgashasadiagnosticd13C= – 40 to -100‰ • signature • Ubiquitousandabundantinsubsurfacesediments,rice • paddies,arctictundra,animalguts(cowstotermites) • • Thermogenicgas has ad13C=– 20 to -40‰ • • Shortresidencetimeinoceanandatmospherewhereit • is consumed (methanotrophy) by bacteria • (methanotrophs) • • Methanotrophs can use O2 (aerobic methanotrophy) • • or SO4 (anaerobic methanotrophy= reverse • methanogenesis) • • Methaneisasignificantgreenhousegasandhas • (recently)beenimplicatedinmanygeobiologicalissues

7. Methane 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/project- pages/hydrates/what.html

8. Methane SEA SURFACE TEMPERATURE PHASE BOUNDARY Gas Hydrate Stability in Ocean Sediments The diagram to the right shows where the same stability curve above crosses the Temperatures of ocean sedments. SEA FLOOR TEMPERATURE (0C) SEDIMENTS GAS HYDRATE PRESENT http://woodshole.er.usgs.gov/project-pages/hydrates/what.html

9. Hydrate seams in mud Hydrate outcropping on seafloor and colonised by chemosynthetic ecosystem Methane actively dissociating from a hydrate mound

10. 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

11. Methane Gas Hydrate: Where is it found? http://woodshole.er.usgs.gov/project-pages/hydrates/what.html

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

13. Methane Ocean 983 (includes dissolved Organics, and biota) Atmosphere 3.6 Land 2790 (includes soil, biota, peat, and detritus) Gas hydrates 10,000 Fossil Fuels 5,000 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

14. 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

15. 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/

16. Ice Worm GOM hydrates derived from thermogenic methane. They are isotopically distinct and impregnated with oil Tubeworms

17. 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. • 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. • Did sea floor sedimentary deposits collapse because hydrate processes and cause landslides and release of gas • by eruptions? • Probably, yes. • 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. • 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

18. Methane Mechanism for sea-level drop to destabilize hydrate http://marine.usgs.gov/fact-sheets/gas-hydrates

19. Methane Mechanism for sea-level rise to destabilize hydrate http://marine.usgs.gov/fact-sheets/gas-hydrates

20. Sediment Core from a methane-rich Monterey cold seep • This is a chemistry “profile” from the core • Methane (µM) Bacteria feed on methane and sulfate Depth into the sediment (cm) Sulfate (mM)

21. As Sulfate (SO4) is • consumed by bacteria, • Hydrogen Sulfide (H2S) • is produced • See How Methane (µM Depth into the sediment (cm) Sulfate (mM)

22. 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

23. How do bacteria influence the physical and chemical environment at seep sites? • CHEMOSYNTHETIC CLAM COMMUNITIES • SO4 • SULFATE SEAWATER SEDIMENT Methane-oxidizing & Sulfate Reducing Bacteria As CH4 and SO4 are consumed, large amounts of hydrogen sulfide and carbon dioxide are produced • CH4 • METHANE

24. How do bacteria influence the physical and chemical environment at seep sites? • CHEMOSYNTHETIC CLAM COMMUNITIES • SO4 • SULFATE SEAWATER SEDIMENT H2S HYDROGEN SULFIDE Methane-oxidizing & Sulfate Reducing Bacteria As CH4 and SO4 are consumed, large amounts of hydrogen sulfide and carbon dioxide are produced • CH4 • METHANE

25. How do bacteria influence the physical and chemical environment at seep sites? • CLAM SYMBIONTS CAN THEN USE THE SULFIDE PRODUCED BY THE BACTERIA • (plus oxygen) TO LIVE • SO4 • SULFATE SEAWATER SEDIMENT Methane-oxidizing & Sulfate Reducing Bacteria • CH4 • METHANE

26. 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

27. 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.

28. Seep clams are no ordinary clams!! Ordinary clam Clam chowder - yum -

29. Seep clams are no ordinary clams!! Ordinary clam Extraordinary clam Clam chowder - yum - • Rotten eggs • - yuck -

30. Adductor muscles Mantle Gills (symbionts) carbon dioxide oxygen Siphons Foot bacterialsymbionts water 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. sediment sulfide

31. In addition to strictly ‘seep’ animals, a variety of other animals benefit from foraging within seep sites. These include…. Sea urchins Crabs Sea cucumbers King crabs Brittle stars

32. Question • •Whatenvironmentalparametersappear • to be important for establishing the • kinds of bacterial and bacterial- • invertebratecommunitiesinMonterey • Bay?

33. 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

34. Methane-Dependent • Communities in the GOM • •Whatenvironmentalparameters • distinguishbacterialandbacterial- • invertebratecommunitiesintheGulfof • Mexico?

35. 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.

36. 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 methyl- sterol pool.

37. Methane-DependentCommunitiesinGOM TABLE 1. Carbon isotopic compositions of seep mussel tissuesa 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.

38. Methane-DependentCommunitiesinGOM Mussel Gill Per Cent Fatty Acid Composition Mussel Mantle • Methylococcus capsulatus Identification of Type I Methanotrophic Signature Fatty Acids in Mussel Gill Tissue

39. Methane-Dependent Communities in GOM • 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 ‰

40. Following the Flow of Carbon Compounds in • Methane-Dependent Communities in GOM Calculated Found symbiont -68 ‰ -70.7 ‰ -68 ‰ -67.3 to -74.1‰ symbiont host -68 ‰ -69.8‰

41. Sulfide-DependentCommunitiesinGOM 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.

42. Sulfide-DependentCommunitiesinGOM 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.