Oceans serve as our climate regulators, cover the sites of fundamental geodynamic, geochemical and biological processes, and offer high-resolution records of the Earth's history. Scientific marine drilling and coring can shed light on both the deep and shallow (sub-) seafloors to advance our knowledge in the Earth and environmental sciences.
The European Science
Foundation's European Collaborative Research (EUROCORES) program EuroMARC is a
tool to boost European planning of international marine coring expeditions and
the preparation of IODP (Intergrated Ocean Drilling Program) or IMAGES
(International Marine Past Global Change Study) proposals. The program consists
of seven collaborative research projects with principal investigators from nine
countries. Fossil reef and carbonate mounds cores are extracted to reconstruct
sea-level and environmental changes. Current ocean dynamics and sediment fluxes
are investigated with the help of sediment traps, and hydrothermal processes of
deep biosphere at mid-ocean ridges get explored.
But how does coring work, and
what actually is done on the cruises?
International marine coring
expeditions are divided into several parts – the pre-, cruise and post-cruise
activities. It's crucial to be 100 percent prepared for the coring, which means
advance planning, starting with getting a slot on one of the few coring and
drilling ships, obtaining territorial drilling permits, making sure all the
required equipment is on board, and getting a good scientific team together.
"We had organizational meetings even before EuroMARC started," explains
Catherine Kissel from the French Atomic Energy Commission, who was the chief
scientist of the AMOCINT (Atlantic Meridional Overturning Circulation during
Interglacials) cruise that took place this past summer.
Often, a site-survey cruise
precedes the main cruise to identify the best spots for the actual coring, and
to get the drill sites approved by bodies like IODP. In order to map the
topography of the seafloor, a multi-beam echo sounder system is used, which is similar
to a fanlike beam covering a huge swath of the seafloor. Additionally, sediment
penetrating systems are employed, which shoot signals with varying energy
pulses and wavelengths that hit the bottom, and are differently reflected
depending on the density of the layers, thus giving a detailed impression of
the layering of the sediments.
Besides the seismics,
autonomous underwater vehicles often are used for more local surveys. "To
make sure we won't damage any living ecosystem, we drop an underwater camera to
see the nature of the seafloor just around the potential drilling site," reveals
Gilbert Camoin, chair of EuroMARC's scientific committee. Especially in the
case of coral reefs, the regulations for drilling are very strict, and pictures
are taken before and afterwards. "There is no impact at all. When you pull
up the pipes, the hole just collapses, and it's even impossible to find it
again," assures Camoin, who investigates coral reefs in both Tahiti
and the Great Barrier Reef.
On the main cruise, the
coring itself takes place, as well as first measurements and part of the
sampling, provided the type of ship allows for it. The cores are extracted in
different ways, at different water depths and of different lengths, depending
on the sediments and the objectives. Short cores of less than 5 feet often are
used to drill coral reefs, and if there are high sedimentation rates going back
in time, long cores are required. Box coring is used for taking surface samples,
as is the so-called multicores instrument with four short cores, where even the
water above the sediment is captured.
Marine coring and drilling is a challenging endeavor.
Needless to say, a good recovery of the cores is essential, however, sometimes
the sediment is lost when pulling out the core, and the so-called core-catcher
at the bottom doesn't shut. The prevailing weather conditions are another
crucial success factor; storms, for example, make operations nearly impossible.
At times, failures of cruises are more man-made, and can range from difficulties
in receiving territorial approval before strict deadlines to failed orders for
indispensable drilling equipment.
EuroMARC Ocean Drilling
December 12, 2008