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Oceanographic Research Expedition to the
Equatorial Pacific Tom Bondra, Brittany Fetter,
Ashley Hague, Rebecca Reese (faculty advisor Dr.
S. Hovan) Geoscience Department, Indiana
University of Pennsylvania
SUMMARY OF PROJECT
SEISMIC SURVEYING
SEDIMENT CORING
Oceanographic research requires the use of
seismic surveying which uses the principles of
sound to create detailed profiles of the
seafloor. These profiles are related to the
relative thickness and density of the sedimentary
layers. Seismic surveying uses low-frequency
sound waves that penetrate deep into the
sediments. Regional patterns of seismic
reflectors allow us to better understand global
climate and oceanographic factors that influence
the deposition of oceanic sediments. In
addition, they help provide information
immediately available to shipboard scientists
useful for the selection of optimal piston coring
locations.
Piston coring allows oceanographers to retrieve
long sediment cores from the seafloor. Most
other coring devices are limited by friction and
extend only about 10 feet below the
sediment-seawater interface. With the use of a
vacuum driven piston corer, sedimentary sections
in excess 50 ft (14m) long are routinely
obtained. Piston coring also provides relatively
undisturbed sediments that allow for long-term,
high-resolution studies of the Earths climate
and ocean history (paleoceanography).
Figure 1. Coring mechanics A piston core and
trigger (gravity) core are connected via a four
foot trigger (tripping) arm.. Once the trigger
core touches the ocean floor it releases the
piston core allowing it to free fall a distance
of about 32 feet. When the core barrel reaches
the seafloor, the piston is pulled from the
bottom of the corer upwards creating a vacuum
that draws sediments up into the core liner.
image modified from http//oceanworld.tamu.edu
/students/forams/forams-piston-coring.htm
Figure1. Generator Injector (G.I.) Air Gun and
Float Two G.I. airguns attached to floats,
create a low frequency sound wave that travels
through the water and into the sea floor. The
sound then reflects off layers of sediment and
returns to the surface where it is received and
recorded by a hydrophone array that is trailed
behind the ship.
Figure 2. Hydrophone Streamer A series of
hydrophones encased in a 400 meter-long plastic
tube is streamed out behind the ship. It
listens for and records sound pulses reflected
off the sediments. Knowing the speed of sound
and the time it takes to travel from the airguns
down to the seafloor and back allows you to
calculate distance or depth.
The IUP Crew (left to right) Tom Bondra,
Rebecca Reese, Ashley Hague, Brittany Fetter and
Dr. Steve Hovan taking a self-portrait while
waiting for a flight to Tahiti. Their Spring
Semester will be spent onboard the R/V Roger
Revelle participating as members of the
scientific party studying the climate records of
the eastern tropical Pacific Ocean.
Research Vessel Roger Revelle The R/V Revelle
is a 273-ft. scientific research vessel operated
by Scripps Institution of Oceanography in San
Diego, CA. Fully equipped with research
facilities especially designed for acoustic
surveying and sediment coring, it sails with a
crew of more than 50 shipboard personnel and
scientists. You can view live shipcam images of
our expedition at http//mercali.ucsd.edu/webimgi
nfo.cgi
On 4 March, 2006 four IUP Geoscience
undergraduate students and professor Steve Hovan,
boarded the research vessel R/V Revelle in
Papeete, Tahiti. Currently, they are at sea in
the equatorial Pacific Ocean working with an
international team of twenty-three scientists
whose primary objectives are to collect a series
of sediment cores and seismic images from the
ocean floor in preparation for a much more
detailed study planned for August of 2007 by the
Integrated Ocean Drilling Program (IODP). The
expedition will be completed on 13April, 2006,
and the ship will return to port in Honolulu,
Hawaii after 37 continuous days at sea. The
Pacific Equatorial Age Transect (PEAT) expedition
will examine records of sedimentary deposits that
have accumulated beneath the ancient equatorial
region. This part of the ocean displays unusual
amounts of high biological productivity that, in
turn, creates a broad mound of sediment deposited
on the seafloor. Primarily composed of biological
skeletal remains, these sediments preserve the
ancient oceanographic and climatic conditions
allow us to study long-term records of the
Earths global average temperature, the growth
and decay of large ice sheets, the chemistry of
the ancient oceans, and the direction and
intensity of major air and sea-surface currents.
As the tectonics plates slowly spread from the
East Pacific Rise, the sediments deposited
beneath the equatorial system slowly drift
northward over time. We have targeted 8 separate
core sites along the ancient equator to give a
better idea of how these important climate
parameters may have changes over the past 40
million years of geological history. IUP students
participating in the expedition will receive 3
credits for a special topics course taught by
Dr. Hovan while at sea (Paleoceanography of the
Pacific Ocean) and 9 internship credits of
Experiential Education. They will work alongside
members of the scientific party in all aspects
of the study including retrieval of sediments
through piston and gravity coring, chemical
analysis of sedimentary calcium carbonate
percentages using a volumetric CO2 gas collection
system, acquisition and analysis of geophysical
seismic data, and visual core description.
Acknowledgments We are deeply indebted to the
captain and crew aboard the R/V Revelle and all
the members of the scientific party for the
AMAT03 Expedition who answered all our questions
with patience and insight. We also thank the
Provosts Office, the Dean of the College of
Natural Sciences and Mathematics, the School of
Graduate Studies and the IUP Foundation for
generous support of this project.
Figure 3. Marine Seismic Profile Seismic
profiles are used to survey sites adequate for
piston coring and future ocean drilling. These
surveys combine low sound wave attenuation rates
with the reliability and accuracy of seismic data
to provide a detailed image of the seafloor and
sedimentary layers.
Figure 2. Deployment of piston and trigger
(gravity) cores Using a trigger core allows the
core barrel of the piston core to impact the
seafloor at a higher speed than it can be lowered
by the winch and therefore provides deeper
penetration into the sedimentary layers.
Figure 3. Core Curation As soon as the cores
are recovered, curation begins. IUP students
Ashley Hague and Tom Bondra and Professor Hovan
help cut the 50 ft long core into more managable
150 cm-long sections. The sections are then
delivered to the MST van for bulk property
analyses (see Multi-Sensor Track System).
Figure 4. Core Halves The core liners are cut
horizontally into an archive half and a working
half. The archive half is preserved for future
studies. The working half is described visually
and then sub sampled by shipboard scientists for
more detailed analysis.
MULTI-SENSOR TRACK SYSTEM
CARBONATE SEDIMENT ANALYSIS
The accumulation of calcium carbonate (CaCO3) on
the seafloor is partly dependent on the amount of
surface biological productivity. In the
equatorial Pacific CaCO3 input is relatively high
compared to other areas of the pelagic ocean.
Equatorial upwelling brings nutrients close to
the surface allowing microscopic plankton to
thrive. But the percentage of calcium carbonate
preserved in sediments is also affected by the
chemistry of deep ocean waters. Since both
factors are related to global climate changes,
analysis of CaCO3 in sedimentary records from the
deep ocean will yield valuable information about
the Earths history.
Immediately after a core is retrieved and cut
into 150 cm sections, it gets passed through the
Multi-Sensor Track (MST) system. The MST is
composed of a series of electronic sensors that
measure different physical properties of the bulk
sediment as the core is pushed along by a track
system. The sensors measure the attenuation of
gamma rays, the thickness of each core, sound
wave speed and amplitude, the electrical
resistivity, and magnetic susceptibility. The
data collected by the MST system help
oceanographers better understand the history of
sedimentation represented by the core material
and provide details of Earths ancient climate.
Figure 1. Volumetric CO2 Analyzer The main
objective of the volumetric carbon dioxide
analyzer is to determine the relative mass of
calcium carbonate in the ocean sediment. This is
done by measuring the amount of carbon dioxide
gas that is released when the calcium carbonate
is reacted with a dilute acid in a closedsystem.
Figure 1. MST Data A downcore plot of bulk
sediment properties at 1 cm intervals. These
data allow stratigraphic correlation between
sites and provide valuable information about the
character and composition of the sediments.
Cruise Track of AMAT03 (Tahiti to Hawaii) The
cruise track traveled approximately 7500 miles
(12,000 km) while surveying the eastern
equatorial Pacific seafloor. Eleven sites were
identified for piston and gravity coring (white
stars). Our current location is approximately
10N of the equator and 136W longitude. Our
expedition ends on April 13, 2006 when we
disembark upon our return to port in Honolulu,
Hawaii.
Figure 3. P-wave velocity core thickness
sensor A compressional sound wave (p-wave) is
generated and measured to determine the amount of
porosity or water content of the bulk sediment by
the speed and amplitude of the wave
Figure 4. Electrical Resistivity Measures
the resistivity of bulk sediment to electrical
impulses. Resistivity varies with the amount of
water found in the sediments thus providing an
estimate of the amount of pore space (porosity).
Figure 5. Magnetic Susceptibility The looped
sensor induces a small magnetic field around core
and measures how well the bulk sediment holds
magnetism. Sediments that contain a greater
proportion of continentally-derived lithogenous
material or volcanic ash are more susceptible to
magnetization while biologically precipitated
sediments are generally non-magnetic. Thus,
magnetic susceptibility data provides a measure
of the relative contribution of each in the
sediments.
Figure 2. Gamma Ray Attenuation (GRA) GRA varies
with the density of the bulk sediments.
Equatorial cores, like those collected by the R/V
Roger Revelle are mainly composed of carbonate
and siliceous rich sediments. Greater
attenuation of a core results from the denser
carbonate sediments as compared with biogenic
silica.
The history of piston coring The first piston
coring cruise in the Pacific Ocean was conducting
during the Swedish Deep Sea Expedition (1948).
Since then, thousands of sediment cores have been
collected yet vast areas of the seafloor have
never been studied. Our expedition (AMAT03) will
examine the ancient equatorial sediments that
have been deposited during the past 45 million
years of Earth History.
Figure 3. Lysocline and Calcium Carbonate
Compensation Depth (CCD) Calcium carbonate
dissolves farther down the water column and very
rapidly in a zone called the lysocline.
Sedimentary calcium carbonate will be preserved
only when the seafloor depth is shallower than
the lysocline. The depth where the dissolution
rate of the calcium carbonate equals the supply
of calcium carbonate is defined as the CCD. The
CCD ranges several km below the ocean surface.
Figure 2. Carbonate Analysis IUP Geoscience
Students Rebecca Reese (left) and Brittany Fetter
(right) work together to measure the calcium
carbonate content of discrete samples taken from
the working half of each core.