Seafloor Exploration Reveals Vast Methane-Driven Oasis Just Miles from Los Angeles

By Jeffrey Marlow | June 29, 2016 10:33 am
The ROV Hercules deploys a geochemical sensor above a small chimney at the Point Dume seep field. (Image: Ocean Exploration Trust)

The ROV Hercules deploys a geochemical sensor above a small chimney at the Point Dume seep field. (Image: Ocean Exploration Trust)

The following is one article in a series of dispatches from the E/V Nautilus. I am serving as a participating scientist on the Central California leg of the 2016 expedition; live footage of our exploration on the seafloor can be found at www.nautiluslive.org.

Malibu, California has long been known as the playground of the rich and famous, a coastal tendril of the 18 million person greater Los Angeles megalopolis. Its beaches serve up consistent sun and waves, movie stars’ mansions line the winding canyon roads, and even the trailer park is an aspirational address.

And yet, just seven kilometers off the coast and 700 meters below the sea surface, a seafloor oasis had gone unseen until just last year. This vast chemosynthetic hotspot, likely fueled by methane seepage into the shallow subsurface, was discovered by the Exploration Vessel Nautilus and its remotely operated vehicle (ROV) Hercules. The Nautilus’ initial reconnaissance effort in 2015 revealed a vast series of colorful microbial mats, extending more than a kilometer along the contour of a submarine canyon.

This year, Nautilus returned to the scene – known as the Point Dume seep field – to collect a more thorough set of samples and poke around for additional noteworthy features. And it didn’t take long: soon after arriving on the seafloor, Hercules’ cameras had spotted a field of bizarre oblong chimneys shrouded in white and orange microbial mats.

“I’ve never seen anything like this,” marvels Peter Girguis, a Professor of Organismic and Evolutionary Biology at Harvard University and the lead scientist on this leg of Nautilus’ explorations. “We’ve seen plenty of hydrothermal vents that form these kinds of chimneys,” he says, “but I’ve never seen these carbonate spires outside of the Black Sea. The mechanics at work are really mysterious.”

The chimneys themselves are likely made of carbonate rock. At most methane seeps, clumps of syntrophic microbes inhabiting anoxic zones a few centimeters beneath the seafloor oxidize methane and convert it to bicarbonate ions. These molecules can link up with calcium or magnesium ions in the seawater to precipitate solid carbonates. Typically, these precipitates seem to form centimeter-scale pebbles, which are then cemented into more extensive, laterally emplaced carbonate shelves.

The constructions found earlier this week appear to be three dimensional projections of the same process. The interior of the football-sized objects is filled with dark sediment, a centimeter-scale carbonate crust keeps everything contained, and sulfide-oxidizing microbial mats provide a white or orange outer coat. A small hole at the top could be where the upflowing fluid emerges.

The Malibu-adjacent seeps demonstrate the remarkable dichotomy between the heavily trafficked and the utterly unexplored – two opposite poles of our known world within several kilometers of each other. And while the Nautilus-driven discovery and exploration of the Point Dume seep field has exposed a novel part of the seafloor to a global audience, many mysteries remain. For one thing, despite the telltale signs of methane seepage – the clams, the microbial mats, the incipient carbonate rock crusts – methane has not yet been confirmed, as no geochemical tests have been conducted. Most seep habitats of this size and profusion are marked by bubble streams, yet neither sonar nor visual surveys have revealed such signals.

And then, of course, there are the rock chimneys. What causes the vertical protrustions, and why are such structures not found at other seep sites? What might these distinctive forms mean for the global methane cycle and greenhouse gas emissions? Girguis believes that the next generation of analytical platforms could help provide answers. “Tools like movable autonomous observatories would be awesome,” he says. “They’d give us a chance to interrogate areas of the deep sea like this for longer periods, and maybe see some episodic gas movement. That would really help us see what’s going on.”

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  • OWilson

    I love the awed humility of these guys.

    They obviously don’t live by the “belief” that sending a few $trillion to the U.N. to redistribute to it’s favorite dictators, will fine tune the planet to within a few hundredths of a degree, exactly by the year 2100.

  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    The Point Dume seep field is lucky not to be saved by concerned activists nor subjected to the Carbon Tax on Everything. Somewhat to the east, Aliso Canyon/Porter Ranch leaked 97,100 metric tonnes of methane, or 6 billion moles, or 4.79 billion standard cubic feet of methane. Methane exhibits a Global Warming Potential of 28-36 over 100 years versus CO2 as 1. The first Enviro-whiner miracle would have been to ignite the plume. Life down in Porter Ranch would then not have been (eventually) evacuated (re Flint, MI and water). The entire child-rich community would not be contaminated with natural gas condensate, including leukemogenic benzene.

    When eventually looking for methane to validate the Point Dume seep field, also look for benzene, Maybe the EPA will shut the whole thing down, preserving it from trespass after removing its occupants.

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The Extremo Files

The Extremo Files traces the science that is pushing the boundaries of biology, from the deep sea to outer space to the brave new world of synthetic biology.

About Jeffrey Marlow

Jeffrey Marlow is a geobiologist exploring the limits of life, from the role of microbes in global elemental cycles to the possibility of life beyond Earth and the brave new world of synthetic biology. He received his PhD from the California Institute of Technology and is currently a Postdoctoral Scholar at Harvard University, where he studies the inner workings of methane-metabolizing organisms.

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