[meteorite-list] Asphalt Volcanoes Provide Stable Home for Life

[Ron Baalke]

https://eos.org/articles/asphalt-volcanoes-erupt-in-slow-motion

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.

[Image]
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 
Chapopote.

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 
that possibility.

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 
quick spurt.

"The asphalts come out very slowly...tectonically slowly," MacDonald 
said.

[Image]
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 
explained.

Interocean Connectivity

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 
added.

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 
noted.

"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.

Conservation Prospects

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.