[meteorite-list] Asphalt Volcanoes Provide Stable Home for Life
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 22 Mar 2016 15:50:17 -0700 (PDT)
Asphalt Volcanoes Erupt in Slow Motion
By Lauren Lipuma
EOS - Earth & Space Science News
March 15, 2016
Natural asphalt seeps on the ocean floor provide a stable home for diverse
marine life that sequesters greenhouse gases.
Underwater volcanoes erupt throughout the world, but in the southern Gulf
of Mexico, they churn out something unusual: cold asphalt instead of hot
lava. First discovered in 2003, these natural oil seeps at the bottom
of the ocean provide a home and fuel for marine life.
Asphalt volcanoes form above natural oil reservoirs deep below the seabed.
Microorganisms degrade the oil, leaving asphalt and methane to seep out
of the ocean floor. This diagram shows how these structures form. Credit:
Jack Cook, Woods Hole Oceanographic Institution
The highly diverse ecosystems that spring up around asphalt volcanoes
do something else: sequester carbon. Federal laws protect deep-sea ecosystems
on the U.S. side of the Gulf of Mexico, but on the Mexico side, no such
protections exist. Because these sites occupy an area that is open to
energy exploration and development, a multinational team of researchers
has suggested that it is time to consider the best model to conserve them.
Pavement Under the Sea
Natural asphalt is a sticky, viscous form of oil. When microorganisms
degrade oil from reservoirs below the seabed, they leave asphalt behind
as a waste product.
A team of German, U.S., and Mexican researchers discovered asphalt volcanoes
at the Campeche Knolls in the southern Gulf of Mexico during an expedition
in 2003. The researchers named the original site, covering more than a
square kilometer in area, Chapopote, the Aztec word for tar.
They found that as the asphalt seeped out of the seabed, it hardened and
solidified in the cold water. Few processes add hard surfaces to the deep
ocean, according to Ian MacDonald, a biological oceanographer at Florida
State University in Gainesville and one of the researchers who discovered
Most organisms that survive in the depths do so by burrowing under layers
of the ocean bottom's sediments, MacDonald said, but asphalts provide
a hard surface on which species such as ice worms and some types of mussels
can grow. In addition, the seeps provide the starting materials for chemosynthesis -
the process by which organisms use energy from inorganic chemical reactions
to make their food.
The German government funded return trips in 2006 and again in 2015 to
further explore the asphalts and characterize the diverse fauna that inhabit
them. MacDonald presented the results of the 2015 expedition at the 2016
Ocean Sciences Meeting in New Orleans.
Slow Ooze, Harboring Hydrates
When the team first discovered the asphalt volcanoes, they found that
the asphalt looked strikingly similar to lava flows on land - asphalt
flows change size, they get wrinkly, they fold over each other, MacDonald
said. They speculated that the asphalt was released quickly in bursts,
but when they returned in 2015, a closer look at the asphalt eliminated
By creating a photo mosaic of the main asphalt flow and examining its
shape and how the asphalt had weathered over time, they realized that
the asphalt oozed slowly out of the seabed, rather than erupting in a
"The asphalts come out very slowly...tectonically slowly," MacDonald
At deep asphalt volcano sites, gas hydrate outcrops, like this one seen
in a panoramic view, form almost instantly. Credit: Ian MacDonald and
Marum Center for Marine Environmental Sciences
Unexpectedly, the research team found large mounds of gas hydrates'clusters
of ice with methane trapped inside - on or near the volcanoes. They also
found massive aggregations of chemosynthetic tube worms tens of meters
long colonizing the hydrate mounds. Some of the tube worms may be hundreds
of years old, they noted.
Gas hydrates would normally dissolve quickly in seawater because the concentration
of methane in the sea is so low, but the researchers suspect the tube
worms help to stabilize the hydrate mounds.
"The tube worms are creating a blanket that essentially sequesters the
gas hydrate and stops it from dissolving into the seawater," MacDonald
Chemosynthetic communities proliferate around hydrocarbon seeps in many
areas along the equator, from the Gulf of Mexico to West Africa's Atlantic
coast and even in the eastern Pacific. Before the Isthmus of Panama closed
off the Atlantic from the Pacific, these waters were joined.
"We think that, at some point, all of these communities were connected,
and we still see a genetic relationship in some of the crustaceans between
these sites," said Elva Escobar, an aquatic ecologist at the National
Autonomous University of Mexico in Mexico City and a member of the research
team. The group is now studying how the organisms' larval stages go
from one place to the other and is gathering Pacific specimens to compare
with those from the other side of the isthmus.
The asphalt ecosystem is an incredibly diverse community that is still
understudied, according to Escobar. "We know very little about how these
communities grow, how they are structured, how they change in time, and
how they interact with the gas hydrates," she said.
Chapopote could provide a model for studying and conserving other chemosynthetic
communities in the deep sea, she said. It "provides a natural laboratory
that allows us to see the diversity of the processes occurring below the
asphalt, within the asphalt, and at the asphalt-water interface," she
Hazards for Oil and Gas Extraction
Mexico recently announced the first energy production lease sales in their
ultradeep offshore waters, but the extensive asphalt pavements and gas
hydrate mounds at those depths pose hazards for drilling operations, according
to the researchers.
If oil and gas companies encounter asphalts while drilling, it's important
to know whether the asphalt they hit is above or below the seafloor, MacDonald
"That will tell you whether the asphalt that you're seeing is likely
to be expansive and extensive, so you hit it in many places with your
drill bit, or it's still in the subbottom, where it might be a potential
resource," he said.
Escobar, who serves on the Legal and Technical Commission of the International
Seabed Authority, said that to conserve both the seeps and the species
they host, researchers need to better understand how far the asphalts
extend and how they change in space and time.
The Mexican government is increasing the extent of marine protected areas
off its coasts, Escobar said, and should also ensure that these unique
ecosystems are included within those zones. According to MacDonald, informing
both the Mexican public and the international community about the importance
of these ecosystems might help protect them.
"I think the international public should be engaged to recognize yet
again an example of the diversity, beauty, and complexity of deep sea
environments," he said.
Lauren Lipuma, Contributing Writer
Citation: Lipuma, L. (2016), Asphalt volcanoes erupt in slow motion, Eos,
97, doi:10.1029/2016EO048095. Published on 15 March 2016.
Received on Tue 22 Mar 2016 06:50:17 PM PDT