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In an Underwater River of Sand and Mud off the Iberian Coast, Six Million Years of Earth History
PRESS RELEASE
For Immediate Release January 18, 2012
In an Underwater River of Sand and Mud off the Iberian Coast, Six Million
Years of Earth History
Scientists have just returned from an expedition onboard the research
vessel JOIDES Resolution, during
which they recovered five kilometers of core samples from an area never before
drilled. The team found new evidence of a deep-earth tectonic pulse, retrieved
a detailed record of climate changes, and made key discoveries that could
influence the future of oil and gas exploration. Lisbon, Portugal –
The
world’s oceans are far from static. Many large currents flow at various depths
beneath the surface, and together, these currents form a global conveyer belt
that transfers heat energy and helps buffer Earth’s climate from the extremes. Critical
gateways in the ocean affect circulation of these major currents. The Strait of
Gibraltar is one such gateway, which re-opened less than 6 million years ago
after being isolated from the Atlantic for several hundred millennia.
Today, deep below the surface,
there is a powerful cascade of Mediterranean water spilling out through the
Strait into the Atlantic Ocean. Because this water is saltier than the Atlantic
– and therefore heavier – it plunges more than 1000 metres down slope, scouring
the rocky seafloor, carving deep-sea canyons and building up mountains of mud
on a little known submarine landscape. These sediments hold a record of climate
change and tectonic activity that spans much of the past 5.3 million years.
Expedition curator Chad Broyles (IODP-USIO/TAMU) leads a
line of technicians carrying a core from the drill floor. [Courtesy of
Integrated Ocean Drilling Program/U.S. Implementing Organization]
An international team of 35
scientists from 14 countries has just returned from an eight-week scientific
expedition onboard the JOIDES Resolution
to collect core samples of these sediments, called contourites because the currents that deposit them closely follow
the contours of the ocean basin. Although the southwest coast of Iberia and the
nearby Gulf of Cádiz have long been
recognized as prime sites to study this record, Integrated Ocean
Drilling Program (IODP) Expedition 339: Mediterranean Outflow is the first to
retrieve sediment core samples from deep below the seafloor here.
“We now have a much greater insight into the
distinctive character of contourites, and have validated beyond doubt the
existing paradigm for this type of sedimentation,” says Dorrik Stow, Co-Chief Scientist
for Expedition 339, from Heriot-Watt University in the UK. “The expedition brought
us many of the eagerly anticipated answers to our questions, as well as wholly
unexpected scientific results.”
The team found evidence for a
“tectonic pulse” at the junction between the African and European tectonic
plates, which is responsible for causing a repeated rising and falling of key
structures in and around the gateway. It also led to strong earthquakes and
tsunamis that dumped large flows of debris and sand into the deep sea. At four
of the seven drill sites, there was also a major chunk of the geologic record
missing from the sediment cores – evidence of a strong current that scoured the
seafloor.
Members of the Expedition 339 science party check out a
core sample in the lab. Pictured, from left to right, are: Roger Flood (SUNY
Stony Brook, USA), Emmanuelle Ducassou (Universite de Bordeaux I, France),
Francisco Jimenez-Espejo (JAMSTEC, Japan), Estefania Llave (Geological Survey
of Spain), Carlos Alvarez Zarikian (IODP-USIO/TAMU), Barbara Balestra (Queens
College, CUNY, USA), Dorrik Stow (Heriot-Watt University, UK) and Maria Sanchez
Goni (Universite de Bordeaux I, France). [Courtesy of Integrated Ocean Drilling
Program/U.S. Implementing Organization]
“We set out to understand how the Strait of
Gibraltar acted first as a barrier and then a gateway over the past 6 million
years,” says Javier Hernandez-Molina, Co-Chief Scientist for Expedition 339
from the University of Vigo in Spain. “We now have that understanding, and a
record of a deep, powerful Mediterranean Outflow through the Gibraltar
gateway.”
The
first drill site, located on the west Portuguese margin, was chosen to provide
the most complete marine sediment record of climate change through the past 1.5
million years of Earth history. These cores cover at least four major ice ages,
and provide a new marine archive to compare against ice core records from
Greenland and Antarctica, among other land-based records.
The JOIDES
Resolution arrives in Lisbon, Portugal on January 16, 2012. [Photo courtesy
Fernando Barriga, ECORD Portugal]
But the
team was surprised to find exactly the same climate signal in the mountains of
contourite mud they drilled in the Gulf of Cádiz. Moreover, because these muds
were deposited much faster than the sediments at the Portuguese margin site,
the record from these cores could prove to yield even richer, more detailed
climate information.
“Cracking
the climate code will be more difficult for contourites because they receive a
mixed assortment of sediment from varying sources,” Hernandez-Molina explains.
“But the potential story that unfolds may be even more significant. The oceans
and climate are inextricably linked. It seems there is an irrepressible signal
of this nexus in contourite sediments.”
In another
surprising turn, the team found a great deal more sand among the contourite sediments
than anyone had expected. The scientists found this sand filling the contourite
channels, deposited as thick layers within mountains of mud, and in a single,
vast sand sheet that spreads out nearly 100 kilometers from the Gibraltar
gateway. All testify to the great strength, high velocity and long duration of the
Mediterranean bottom currents. Moreover, the find could impact future oil and
gas exploration.
“The
thickness, extent and properties of these sands make them an ideal target, in
places where they are buried deeply enough to allow for the trapping of
hydrocarbons,” Stow explains. The sands are deposited in a completely different
manner, in channels and terraces cut by bottom currents; in contrast, typical
reservoirs form in sediments deposited by downslope “turbidity” currents. “The
sand is especially clean and well sorted, and therefore very porous and
permeable. Our findings could herald a significant shift in future exploration
targets.”
About IODP
The Integrated Ocean Drilling Program (IODP) is an
international research program dedicated to advancing scientific understanding
of the Earth through drilling, coring, and monitoring the subseafloor. The JOIDES Resolution is a scientific
research vessel managed by the U.S. Implementing Organization of IODP (USIO).
Together, Texas A&M University, Lamont-Doherty Earth Observatory of
Columbia University, and the Consortium for Ocean Leadership comprise the
USIO. IODP is supported by two
lead agencies: the U.S. National Science Foundation (NSF) and Japan's Ministry
of Education, Culture, Sports, Science, and Technology. Additional program
support comes from the European Consortium for Ocean Research Drilling (ECORD),
the Australia-New Zealand IODP Consortium (ANZIC), India’s Ministry of Earth
Sciences, the People's Republic of China (Ministry of Science and Technology),
and the Korea Institute of Geoscience and Mineral Resources. For more
information, visit www.iodp.org.
In an Underwater River of Sand and Mud off the Iberian Coast 
