"New study challenges prevailing theory about how deep-sea vents are colonized"… And hydrothermal oil!

Guest post by David Middleton


July 24, 2017

New study challenges prevailing theory about how deep-sea vents are colonized

An article just published in the Proceedings of the Royal Society B describes two remarkably different hydrothermal vent fields discovered in the southern Gulf of California. Despite being relatively close together, these vents host very different animal communities. This finding contradicts a common scientific assumption that neighboring vents will share similar animal communities. Instead, the new paper suggests that local geology and the chemistry of the vent fluids are important factors affecting vent communities.


Though neighbors, the Alarcón Rise and Pescadero Basin vent fields are geologically very different. The seafloor along the Alarcón Rise is covered in young, fresh lava, and the fluids spewing out of the vents are very hot (up to 360 degrees Celsius) and rich in metal sulfides that form dark, crumbly chimneys known as “black smokers.” Animals at the Alarcón Rise are similar to locations further south (almost 300 kilometers) on the East Pacific Rise.

In Pescadero Basin, however, hydrothermal-vent fluids pass through thick layers of seafloor mud. As the hot hydrothermal fluid flows through this mud, it “cooks” organic material, forming methane (natural gas) and oil-like hydrocarbons. The Pescadero Basin vents contain very little sulfide, and the superheated fluids produce giant, light-colored, carbonate chimneys streaked with dark, oily hydrocarbons.



Very interesting… However, I quickly lost interest in the biological aspects of the article when I read this bit:

In Pescadero Basin, however, hydrothermal-vent fluids pass through thick layers of seafloor mud. As the hot hydrothermal fluid flows through this mud, it “cooks” organic material, forming methane (natural gas) and oil-like hydrocarbons. The Pescadero Basin vents contain very little sulfide, and the superheated fluids produce giant, light-colored, carbonate chimneys streaked with dark, oily hydrocarbons.

Could this be actual evidence of “abiotic” or “abiogenic” oil?

No.  Of course it isn’t.  If anything this might just be a “nail in the coffin” for abiotic oil.

The “oil-like hydrocarbons” were associated with hydrothermal-vent fluids which “pass through thick layers of seafloor mud”  in the Pescadero Basin.

Just 75 km to the south, the seafloor of the Alarcón Rise is covered with layers of relatively fresh lava flows and very little sediment.  The Alarcón Rise hydrothermal vents are run of the mill black smokers, with no evidence of “hydrothermal oil.”



This map shows the major known hydrothermal vent sites in and around the Gulf of California. Even though the Pescadero Basin and Alarcón Rise are relatively close, they host very different animal communities. Base map: Google Earth

Here’s an older article about the initial discovery of the Pescadero Basin hydrothermal vents:

June 2, 2015

MBARI researchers discover deepest known high-temperature hydrothermal vents in Pacific Ocean

In spring 2015, MBARI researchers discovered a large, previously unknown field of hydrothermal vents in the Gulf of California, about 150 kilometers (100 miles) east of La Paz, Mexico. Lying more than 3,800 meters (12,500 feet) below the surface, the Pescadero Basin vents are the deepest high-temperature hydrothermal vents ever observed in or around the Pacific Ocean. They are also the only vents in the Pacific known to emit superheated fluids rich in both carbonate minerals and hydrocarbons. The vents have been colonized by dense communities of tubeworms and other animals unlike any other known vent communities in the in the eastern Pacific.


Reflecting on the discovery, Clague commented, “Before the AUV survey of Pescadero Basin, all we knew was that this area was really deep and filled with sediment. I was hoping to find a few outcrops of lava on the seafloor. But we got lucky. The vent field was right on the edge of our survey area, along a fault at the western edge of the basin.”


The AUV and ROV dives showed that the new field extends for at least 400 meters (one quarter mile) along this fault. Within this area the researchers found at least three active hydrothermal chimneys up to 12 meters (40 feet) tall, as well as dozens of low mounds that are most likely collapsed chimneys.

After his ROV dive, Clague noted, “This site was not at all what I was expecting.” For one thing, the fragments of chimneys that the ROV brought back to the surface were quite different from those collected at other vents in the area. The Pescadero chimneys consisted entirely of light-colored carbonate minerals instead of the dark sulfide minerals that are abundant in hydrothermal chimneys elsewhere in the Gulf.

The Pescadero Basin is only the second place in the world where carbonate chimneys (instead of ones made primarily of sulfides) have been found in the deep sea. The other known location is the “Lost City” vent field in the middle of the Atlantic Ocean, at a spot on the Mid-Atlantic Ridge.

The geologists also noticed that their rock samples smelled like diesel. They hypothesize that hot hydrothermal fluids migrating upward through the thick sediments of the Pescadero Basin “cook” organic matter in the sediment, converting it into petroleum-like hydrocarbons—a process that has been observed at several other vents in the Pacific. Hydrocarbons may provide nutrition for the unusual microbes that thrive at these vents.



This is a map of total sediment thickness for most of the world’s oceans from NOAA:


Whittaker, Joanne, Alexey Goncharov, Simon Williams, R. Dietmar Müller, German Leitchenkov (2013) Global sediment thickness dataset updated for the Australian-Antarctic Southern Ocean, Geochemistry, Geophysics, Geosystems. DOI: 10.1002/ggge.20181

I enlarged the area comparable to the MBARI map and posted the four vent systems on it.  Note that the basins with thick sediments exhibit evidence of petroleum-like substances associated with hydrothermal vents.  The vents associated with the sediment-deprived rises do not.

Hydrothermal oil

Petroleum-like substances have been associated with hydrothermal vents in basins with thick organic-rich sediments. However nearby hydrothermal vents with little to no sediment cover (rises) do not exhibit evidence of “hydrothermal oil.”

Furthermore, the “hydrothermal oil” of the Guaymas Basin is extremely young and relatively rich in 14C…

Nature 342, 65 – 69 (02 November 1989); doi:10.1038/342065a0

Hydrothermal oil of Guaymas Basin and implications for petroleum formation mechanisms


*Refineria de Petroleo Concon, Casilla 242, Concon, Chile

†Petroleum Research Group, College of Oceanography, Oregon State University, Corvallis, Oregon 97331, USA

PETROLEUM-LIKE hydrocarbons have been detected in thermally altered Recent sediments of Guaymas Basin1–5 and petroleum-like hydrocarbon impregnations were found in hydrothermal mounds on the sea floor and associated with hydrothermal vent emissions5–9. Here we report the evaluation of such a hydrothermal oil, which we find to be similar to conventionally exploited crude oils. Its young geological age (< 5,000 yr, 14C) 10 indicates that a significant fraction of the organic carbon in the oil has completed the transformation from biomass to migrating oil in less than 5,000 years, thus limiting the oil generation, explusion and migration processes to a geologically short timescale. We estimate the generation potential of such hydrothermal oil and discuss its implications to our understanding of the petroleum generation, expulsion and migration mechanisms.


The Lost City hydrothermal vent on the Mid-Atlantic Ridge and the Pescadero Basin are the only two known places where carbonate (rather than sulfide) chimneys have been found.

Lost City is also possibly an example of the Fischer-Tropsch process is at work…

Deep-ocean vents are a source of oil and gas

Hydrocarbons bubble up from the mid-Atlantic’s Lost City.

Rachel Courtland

Undersea thermal vents can yield unexpected bounty: natural gas and the building blocks of oil products. In a new analysis of Lost City, a hydrothermal field in the mid-Atlantic, researchers have found that these organic molecules are being created through inorganic processes, rather than the more typical decomposition of once-living material.

Most of the planet’s oil and natural gas deposits were created when decomposing biological matter is ‘cooked’ in high temperatures underground. But non-biological hydrocarbons have also been found deep inside the Earth, where chemical processes create the molecules from inorganic sources such as rock.


Among other measurements, the team analysed the amount of carbon-13 in methane, which contains one carbon atom, and in hydrocarbons containing two, three, and four carbon atoms. As the number of carbon atoms rose, the concentration of carbon-13 fell — the opposite trend to that seen in biologically derived hydrocarbons.

Instead, the pattern of isotopes suggest that a chemical process called the Fischer-Tropsch process is at work in Lost City, creating bigger and bigger hydrocarbons in the hydrogen-rich environment. Although the concentrations were too low to detect without a filter, small amounts of larger hydrocarbons such as kerosene and octane may also be produced.

The team also found that the methane in Lost City contained no carbon-14, suggesting the carbon source for the hydrocarbons comes from within the mantle, far away from organisms that might have had contact with the global carbon cycle at the surface.



Setting aside the fact that “the building blocks of oil products” are not the same thing as oil (in much the same manner that a 2×4 is not the same thing as a house)… The carbon in the Lost City hydrocarbons is either so old that carbon-14 is undetectable or it has never “had contact with the global carbon cycle at the surface.”  So, the methane and the traces of hydrocarbons at Lost City were almost certainly sourced from inorganic substances.  While the traces of “hydrothermal oil” in the Pescadero and Guaymas Basins were almost certainly sourced from organic substances.



57 thoughts on “"New study challenges prevailing theory about how deep-sea vents are colonized"… And hydrothermal oil!

  1. Could these hydrocarbons be coming from thermally active natural seeps? Such seeps are common along the coast of California.

    • It appears that the hydrothermal fluids are “cooking” the organic matter in the sediment and carrying the petroleum-like liquids to the seafloor.
      Vents that don’t have significant organic-rich sediment cover aren’t generating the petroleum-like liquids.

      • “So, the methane and the traces of hydrocarbons at Lost City were almost certainly sourced from inorganic substances. While the traces of “hydrothermal oil” in the Pescadero and Guaymas Basins were almost certainly sourced from organic substances.”-D M
        Doesn’t this point to multiple pathways for hydrocarbon formation?

        • There have always been multiple pathways. However they all involve “cooking” organic matter in sediment and/or sedimentary rock.

      • It would be nice to know if there were any samples of sediments taken not near the vents so that an uncooked sample of sediment could be assessed against the “cooked” sediments. It would be useful to know if the hydrocarbons were already extant and merely lying within the sediments awaiting heating to release them or is this indeed the generation of hydrocarbons from other organic compounds.

      • David Middleton, can you explain the apparent contradiction in the following two statements?
        1) “So, the methane and the traces of hydrocarbons at Lost City were almost certainly sourced from inorganic substances.
        2) “There have always been multiple pathways. However they all involve ‘cooking’ organic matter…”
        If all sources of hydrocarbons involve cooking organic matter, how can the hydrocarbons at Lost City be sourced from inorganic substances?

        • Yes. I should have said that the multiple pathways of petroleum formation always include “cooking” organic matter.
          Clearly methane and traces of heavier simple hydrocarbons can be formed from non-biological material.

  2. “the fluids spewing out of the vents are very hot (up to 360 degrees Celsius)” – and how do these vents influence the temperature of the oceans?
    As an aside ..
    “The Log from the Sea of Cortez” is an English-language book written by American author John Steinbeck and published in 1951. It details a six-week (March 11 – April 20) marine specimen-collecting boat expedition he made in 1940 at various sites in the Gulf of California

    • It’s the opposite of Thomas Gold.
      If the hydrothermal oil was coming out of the Mid-Atlantic Ridge, East Pacific Rise and Alarcón Rise, instead of the Pescadero and Guaymas Basins, it would be “shades of Thomas Gold.”

    • There are hydrocarbon seas on Titan, probably of abiogenic origin. Why not on the Earth?

      • 1) Methane and other simple hydrocarbons and petroleum are two very different things.
        2) There is abundant evidence of “hydrocarbon seas on Titan”… Almost certainly of abiogenic origin.
        3) Apart from methane and traces of heavier simple hydrocarbons, there is no evidence of inorganically sourced oil on Earth.
        This doesn’t mean it’s impossible. However the four vents in the Gulf of California area are relatively close to one another. The two vents in basins filled with organic-rich sediments are associated with hydrocarbon liquids very similar to petroleum. The two vents on rises with little to no sediment and mostly volcanic rock seafloors are not associated with hydrocarbon liquids very similar to petroleum.

      • “There are hydrocarbon seas on Titan, probably of abiogenic origin. Why not on the Earth?”
        Short answer: Earth’s too hot.
        Google “Oil Window”
        Vastly simplified, the idea is that organic material gets stashed in sediment. If it doesn’t get exposed to much heat/pressure, it doesn’t change much and you end up with asphalt, heavy “oils” or waxlike solid kerogen. Cook it a bit and apply some pressure and the hydrocarbon chains fracture yielding lighter oils, short chain gases like butane, and eventually methane. Oil companies tend to look for oil in rocks that whose temperature-pressure history puts them in a “window” where the hydrocarbons will likely be light enough to flow but not to be converted to natural gas which doesn’t usually equate to anywhere near as much instant wealth.
        The inside of the Earth is very hot and pressures are very high. So even if hydrocarbons are forming, and finding their way to the surface they will probably be mostly methane and ethane. … Probably … most likely … maybe

  3. I try to learn something every day. Even though I grew up in Alberta, with horsehead pumps here and there, and sometimes stacks of yellow bricks or blocks where sulphur had been removed; and even though geology was my lab science; I never learned much about the oil and gas business and geology. I appreciate your posts.

  4. Do we know the amount of geothermal heat energy absorbed & released by oceans and by doing so making important contribution to natural variability on scale ranging from decades to millennia ?
    “It may not be obvious while lying in the sun on a hot summer’s day, but a considerable amount of heat is also coming from below you – emanating from deep within the Earth. This heat is equivalent to more than three times the total power consumption of the entire world and drives important geological processes, such as the movement of tectonic plates and the flow of magma near the surface of the Earth. But despite this, where exactly up to half of this heat actually comes from is a mystery.”
    … or so says Jocelyn Monroe (Department of Physics and Laboratory for Nuclear Science, Massachusetts Institute of Technology) and others.
    science is still ‘unsettled’ ?

    • 30 years ago the geothermal heat flux was estimated at 70 mW/m2 in average. Today the estimate is 90 mW/m2. It is highly variable both in space and in time. Much less than the heat coming from the Sun.

      • Although the solar variability is continuously and incorrectly dismissed as the main cause of natural variability, it might be wrong to totally dismiss geothermal.
        From the article linked above:
        “It could also help unravel the longstanding mystery of what source of heat powers the convection (transfer of heat by movement of fluids) in the outer core that generates the Earth’s geomagnetic field..”
        Geothermal ‘effect’ may provide explanation for the association of the global temperature and the earth’s magnetic field variability with R^2=0.8.
        Geothermal energy release is concentrated along the Pacific’s ‘ring of fire’ and the mid Atlantic, the areas of major ocean currents circulation.
        As you say ‘highly variable both in space and in time’; the variability in time may affect the oceans currents circulation and so energy transport from equatorial to the sub/ & polar regions.

    • vukcevic August 4, 2017 at 1:10 pm
      vukcevic August 4, 2017 at 2:40 pm
      “”Although the solar variability is continuously and incorrectly dismissed as the main cause of natural variability, it might be wrong to totally dismiss geothermal.””
      Thanks for the comments Vuks.
      The two main drivers…

    • The science is never settled. Least of all concerning the unexplored mantle, core and deep crust.

  5. For Pete’s sake! Carbon-14 has a half-life in the neighborhood of 6000 years. You can only use C-14 dating back to about 60,000 years ago. Any decent ocean sediment is older than that. Not finding C-14 in Lost City emissions says almost NOTHING about abiogenesis. You might have better luck with the C-13, though.

    • They’re looking at the carbon isotopes in the methane, not in the sediments. Sediments near the seafloor are in contact with the active carbon cycle. CH4, CO2 and other gases present in those sediments will have some 14C. The 13C ratio in the CH4 and heavier HC’s exhibits a non-biological signature as well.

  6. The carbon-14 absence in the Lost City emissions says little more than that the seafloor sediments are older (by and large) than 60,000 years. That’s something like ten half-lives of an exceedingly rare isotope. Biogenesis or abiogenesis, there ain’t gonna be much C-14.

    • They’re measuring the carbon isotope ratios in the CH4 and traces of heavier HC’s… Not the carbon isotopes in the sediments.

  7. Spending a few hundred million $ looking for abiotic oil could be a good gamble. I always like to stand back (a few million km) and notice that we appear to inhabit a VERY VERY thin outer layer of the 3rd rock.

  8. The absence of C14 is not a very strong argument for abiogenic origin. C14 has a half-lif of about 5,700 years. This means that after 200,000 years (which is a quite short time in geological terms, less than two ice-age cycles) not even one C14 atom in a billion is left.

  9. Titan’s hydrocarbons…

    Chemical composition of the lakes
    According to Cassini data, scientists announced on February 13, 2008, that Titan hosts within its polar lakes “hundreds of times more natural gas and other liquid hydrocarbons than all the known oil and natural gas reserves on Earth.” The desert sand dunes along the equator, while devoid of open liquid, nonetheless hold more organics than all of Earth’s coal reserves.[20] It has been estimated that the visible lakes and seas of Titan contain about 300 times the volume of Earth’s proven oil reserves.[21] In June 2008, Cassini’s Visible and Infrared Mapping Spectrometer confirmed the presence of liquid ethane beyond doubt in a lake in Titan’s southern hemisphere.[22] The exact blend of hydrocarbons in the lakes is unknown. According to a computer model, three-quarters of an average polar lake is ethane, with 10 per cent methane, 7 per cent propane and smaller amounts of hydrogen cyanide, butane, nitrogen and argon.[23] Benzene is expected to fall like snow and quickly dissolve into the lakes, although the lakes may become saturated just as the Dead Sea on Earth is packed with salt. The excess benzene would then build up in a mud-like sludge on the shores and on the lake floors before eventually being eroded by ethane rain, forming a complex cave-riddled landscape.[24] However, the chemical composition and physical properties of the lakes probably varies from one lake to another (Cassini observations in 2013 indicate Ligeia Mare is filled with a ternary mixture of methane, ethane, and nitrogen and consequently the probe’s radar signals were able to detect the sea floor 170 m below the liquid surface).[25]
    No waves were initially detected by Cassini as the northern lakes emerged from winter darkness (calculations indicate wind speeds of less than 1 metre per second should whip up detectable waves in Titan’s ethane lakes but none were observed). This may be either due to low seasonal winds or solidification of hydrocarbons. The optical properties of solid methane surface (close to the melting point) are quite close to the properties of liquid surface however the viscosity of solid methane, even near the melting point, is many orders of magnitude higher, which might explain extraordinary smoothness of the surface.[26] Solid methane is denser than liquid methane so it will eventually sink. It is possible that the methane ice could float for a time as it probably contains bubbles of nitrogen gas from Titan’s atmosphere.[27] Temperatures close to the freezing point of methane (90.4 Kelvins) could lead to both floating and sinking ice – that is, a hydrocarbon ice crust above the liquid and blocks of hydrocarbon ice on the bottom of the lake bed. The ice is predicted to rise to the surface again at the onset of spring before melting. Since 2014, Cassini has detected transient features in scattered patches in Kraken Mare, Ligeia Mare and Punga Mare. Laboratory experiments suggest these features might be vast patches of bubbles caused by the rapid release of nitrogen dissolved in the lakes. This phenomenon is predicted to occur as the lakes warm or whenever methane-rich fluids mix with ethane-rich ones due to heavy rainfall.[28] An alternative explanation is the transient features may be shallow capillary waves (ripples) moving at about 0.7 meters per second and at heights of about 1.5 centimeters.[29] Cyclones driven by evaporation and involving rain as well as gale-force winds of up 20 meters per second (= 72 kph) are expected to form over the large northern seas only (Kraken Mare, Ligeia Mare, Punga Mare) in northern summer during 2017, lasting up to ten days.[30]

    Ethane, methane, propane and butane are simple hydrocarbons. Benzene is the simplest aromatic hydrocarbon. There is also evidence of PAH-type (polycyclic aromatic hydrocarbons) compounds on Titan. These are not complex hydrocarbons.
    Titan, like the Lost City hydrothermal vent system has some of the building blocks for petroleum.
    Petroleum is a mixture of several complex hydrocarbons.

    • “Titans’ hydrocarbons”
      “according, computer models, might explain, estimated, may be, probably, is possible, is predicted, alternative explanation ” etc,etc, etc
      Sounds like the dialog from “Ancient Aliens” or some AGW screed, tiresome, unscientific hyperbole.

      • Until we take a physical sample of Titan’s hydrocarbons, we can’t know what the mixture is.

  10. The team also found that the methane in Lost City contained no carbon-14, suggesting the carbon source for the hydrocarbons comes from within the mantle, far away from organisms that might have had contact with the global carbon cycle at the surface.
    No. Lack of C14 in a hydrocarbon sample does not point to a mantle origin.
    with a half-life of 5730 years,
    after 100,000 years, one C14 in the original 180,000 C14 remains.
    after 150,000 years, one C14 in 76,000,000 remain.
    after 200,000 years, one C14 in 32,000,000,000 remain.
    after 250,000 years, one C14 in 13,600,000,000,000 remain (13.6 trillion.)
    after 500,000 years one C14 in 1.8*10^26
    after 1,000,000 years one C14 in 3.4*10^52
    And on day one, C14 is only 1 part per trillion of total carbon.
    In practice, ages older that 50,000 years is beyond the range of C14 dating. But even the detection of C14 becomes technically impossible before a million years in age and most oil is source from material tens to hundreds of million years old.

  11. There was an attempt to reproduce the hydrothermal processing of biological (and other) material into oil. The pilot facility used turkey waste.
    Whilst a promisng and interesting technique, the economics compared to simply pumping the stuff up from the ground mean that these technologies are unlikely to succeed for production of fuels.

  12. Very interesting article David. Well done. And well illustrated. One thing about these hydrothermal vent communities that bothers me from time to time is how the critters — tube worms and such — find them. I gather that a given vent may have a rather short lifetime in geological terms — a few thousand years? And the vents are often quite some distance from the closest similar structure. How does a new vent get colonized?

    • Many stationary oceanic lifeforms produce plankton sized mobile offspring that float until they find a good place to settle, or get eaten. Coral, for example. I don’t know that’s the case for tube worms, but would expect it…
      These can be more cold tolerant if needed, swaping to hot metabolism when settled.
      Some even just dump eggs and sperm into the ocean and hope it mixes in the right spot… yes, swimming in the ocean puts you in the middle of a giant orgy and floating nursery.

  13. Years ago, 15-20 maybe, there was an article in Proceedings of the National Academy of Science about producing oil from high temperature high pressure on carbonate rocks.

  14. There’s plenty of methane in space. There is also black tarry stuff on comets and there are carbonaceous asteroids and meteorites. I have no trouble believing that methane was trapped when the earth formed and as Leveut said there have been lab experiments where higher hydrocarbons were formed by methane in the presence of carbonate rocks (and iron oxide). I wish people would read Gold and look at what he actually said, not what somebody else said he said.
    About those deposits of water ice on the Moon at the poles in cold traps? There will be black tarry stuff there too.

  15. It isn’t just F.T. that gives complex hydrocarbons from inorganic stuff. Various Zeolites (a kind of catalytic rock) do it too.
    We know, absolutely, that long and complex hydrocarbons exist in space, including amino acids.
    Now I’m agnostic in the Abiogenic Wars, but to blanket assert abiogenic doesn’t exist when we know the chemistry and materials do, is just silly bias.
    It IS accurate to say that substantially all the petroleum found looks like it is derived from biological source materials (mostly algae, not dinosaurs); and that that is THE best theory for finding more.
    BUT, that in no way prevents, for example, the subduction of carbonate rock and water of hydration in the Farralon Plate from making hydrocrabons as it gets cooked, or those being upgraded to longer chains via FT or zeolite like paths. Bacteria exist in deep rocks and all sorts of biomarkers could be added as that fluid percolates up high enough to be found.
    Highly unlikely, but that is not a zero.
    So no, it isn’t any nail in any coffin. Likely there will never be a resolution unless a clearly abiogenic find is made, simply because proving a negative is very hard.

  16. For molecule to be defined ‘organic’, it’s enough that the molecule contains carbon, hydrogen and often oxygen. These all are among the six most abundant elements in the universe. It would defy Occam’s razor if Earth’s mantle didn’t contain them irrespective of biosphere.

    • Organic just connotes a hydrogen-carbon bond.
      While organic chemistry is often associated with life. It’s not exclusively related to life.

    • It’s not. It’s also not petroleum. Titan has seas of simple hydrocarbons. Oil is a mixture of complex hydrocarbons. I explained this in detail in another comment.

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