Leg 185
An Expedition to a Subduction Factory: ODP Searches for Bacteria in Ancient Rock
28 June 1999
An Ocean Drilling Program (ODP) expedition dedicated to the ocean's
deepest trenches, the Mariana and Izu-Bonin, ended June 15 in the
port of Yokohama, Japan. These trenches form the boundary between
colliding tectonic plates, and cataclysmic events such as
earthquakes, tsunamis, and explosive volcanism. At the Mariana and
Izu-Bonin trenches, these collisions cause one plate to slide under
the other plate, a process known as subduction. As one plate is
subducted deep into the Earth, the material (sediments) on the plate
and the plate itself are consumed and then re generated to form
materials that are expelled onto the Earth's surface in volcanoes.
This process is part of an important Earth chemical cycle that
scientists have dubbed, "the subduction factory."
The subduction factory is a dynamic system in which the subducting
seafloor and overlying mantle are recycled and processed into new
products on the upper plate. Beneficial products such as ore
deposits are part of the factory's outputs. In order to understand
the formation processes of previous ores and the timing and
magnitudes of cataclysmic events, scientists need to know the true
workings of the subduction factory. As in all factories, a knowledge
of the most basic information is needed: what goes in versus what
goes out. Or in scientific language, researchers need to understand
the mass balance of chemicals cycled through Earth.
The scientific goal of this expedition was to determine important
missing gaps in the factory cycling system along the Mariana and
Izu-Bonin arcs. These gaps include an incomplete understanding of the
aging process of the uppermost layer of the solid Earth, the flow of
materials through the zone between deep sea trenches and volcanic
arc, and the fluid circulation at active margins. The Mariana and
Izu-Bonin arcs are ideal for subduction recycling studies because
both are created by the same subducting plate, yet have distinct
geochemical signatures. Studies of the relative amounts of several
important components in the subducted plate (e.g., water, carbon
dioxide, and trace metals) were used to determine whether the
chemical differences between the two arc systems are the result of
different inputs to the two trenches or different behavior of the
subduction factories.
Another objective of this expedition was to sample the Earth's deep
biosphere, and, in particular, to establish protocols for studying
these potentially new life forms. It is currently speculated that a
large part of the Earth's biosphere is locked beneath the ocean's
floor. The discovery of bacteria, living in extreme conditions of
pressure and temperature (extremophiles), has important implications
for understanding the origins of life, discovering new life forms,
understanding the link between these Earth-thriving bacteria and the
formation of oil and gas, and Earth's carbon budget.
Two deep-water sites were drilled and studied during Leg 185. The
research team sampled and measured the in situ conditions of the
upper alteration zone at an existing ODP Hole (801C), located seaward
of the Mariana Trench, and the entire sedimentary section into
basement at a new site (BON-8A) located near the Bonin Islands. These
sites were drilled to depths as great as 900 m below the seafloor in
up to 6 km of water. Samples were retrieved from these sites that
represent the oldest rocks ever collected from the ocean floor and
some of the deepest rocks ever recovered from the ocean crust. The
chemical composition of the recovered rocks were measured as were
properties of the borehole using special logging techniques.
Scientists discovered that patterns in the basalts collected at
depths of 590 to 920 m below the seafloor were characteristic of
those associated with life forms discovered previously in other
younger and shallower parts of the ocean floor. This suggests that
life can exist and survive in very high pressure settings and in
rocks that formed 167 million years ago. Following the expedition,
scientists will continue to study the microbes by culturing and
extracting DNA from microbes in rock, sediment and water samples.
Samples collected by the scientists could potentially be contaminated
by the actual drilling process. One of the scientists' objectives
was to evaluate the amount of contamination in the recovered rocks
and sediment. This was accomplished by injecting tracers into the
seafloor as they drilled.
Challenges of the Deep
During Leg 185, ODP drilled in one of the deepest parts of the
world's ocean. The sites were located in water depths ranging from
5.7 to 6 km. These water depths combined with the drilling depths
pushed the state-of-the-art deep water drillship, JOIDES
Resolution, beyond any previous drilling. The ship's derrick,
designed to carry the weight of 9,000 m of steel drill pipe,
successfully worked at its maximum capacity breaking a world record
in deep water drilling.
The research vessel, JOIDES Resolution, departed for its next
expedition to the Japan Trench on June 19. The goal of Leg 186 is to
install long-term, deep, seabed observatories for the study of
earthquakes and measuring properties of the Earth's mantle.
ODP
The Ocean Drilling Program, an international partnership of
scientific institutions and governments, explores the Earth's history
and evolution. The Ocean Drilling Program is funded principally by
the U.S. National Science Foundation, with substantial contributions
from its international partners. These include the Federal Republic
of Germany, Japan, the United Kingdom, the Australia/Canada/Chinese
Taipei/Korean Consortium for Ocean Drilling, the European Science
Foundation Consortium for Ocean Drilling (Belgium, Denmark, Finland,
Iceland, Italy, The Netherlands, Norway, Portugal, Spain, Sweden, and
Switzerland), France and the People's Republic of China. The program
is managed by Joint Oceanographic Institutions, a consortium of 11
U.S. institutions, Texas A&M University is responsible for
science operations, and Lamont-Doherty Earth Observatory of Columbia
University is responsible for logging services.
Scientists Contacts:
Dr. Terry Plank, Co-Chief
Department of Geology-Geophysics Program
University of Kansas, USA
Internet: tplank@kuhub.cc.ukans.edu
Work: (785) 864-2725
Fax: (785) 864-5276
Dr. John Ludden, Co-Chief
Centre de Recherches Pétrographiques et Géochimiques
(UPR 9046)
France
Internet: ludden@crpg.cnrs-nancy.fr
Work: (33) 3-83-59-42-13
Fax: (33) 3-83-51-17-98
Dr. Carlota Escutia, Staff Scientist
Ocean Drilling Program
Internet: carlota_escutia@odp.tamu.edu
Work: (979) 845-0506
Fax: (979) 845-0876
In addition, the ODP Web Site includes information on this leg
(Leg 185 Scientific Prospectus) http://www.oceandrilling.org
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