This
section is divided into 3 parts; Who, How
and Why
This Chapter examines the transformation from Marine Studies into Marine Science, focussing on the changing perceptions, methods and pioneers of the study of the oceans.
As we have mentioned, the first systematic sampling of the sea floor was 1872-76 by HMS Challenger but it wasn’t until the 1960’s, that technical advances allowed scientists to sample the layers of sediment and rock beneath the sea floor. These layers record the history of the ocean basins. Since WWII many research vessels have contributed to exploration of the ocean and the ocean floor. From 1968 until 1983, the ship that dominated ocean drilling research was the Glomar Challenger (Deep Sea Drilling Project). But by the early 1980s, it was reaching the end of its useful life. Researchers who were worried that the deep ocean drilling program would end with the scraping of the Glomar convened the first international Conference on Scientific Ocean Drilling in 1981. Under the sponsorship of the Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES) the scientists identified important projects that could not be completed without a long-term, worldwide ocean drilling program.
The U.S. National Science Foundation supported the scientists conclusions and agreed to provide the major share of funding for an international Ocean Drilling Program (ODP) aboard a new vessel with enhanced capabilities. They found what they were looking for in an advanced drillship JOIDES Resolution (named after the ship Captain Cook used in his ocean explorations more than 200 years ago). The Resolution is 143m long and 21m wide. Amidships the drilling rig towers 64.5m above the waterline--the approximate height of a 20 story building. Beneath the drill rig is the "moon pool" - a 7m square opening that allows the drill pipe to be lowered through the bottom of the hull. The ship carries 10,000 m of drill pipe and can drill in water as deep as 8,235m. Each pipe joint is about 28m long and weighs about 874 kilos. The drill crew threads each section to the drill string as it descends. The process of lowering the drill bit, which is attached to the end of the drill string, takes about 12 hours in 5,500m of water. So far the deepest water Resolution has drilled in is 6,200m and the furthest it has penetrated the seafloor is 2.2km.
Since 1985 the Resolution has been circling the globe, drilling
core samples from the sediments and igneous rocks buried on the seafloor. The
ship has drilled in every sea, from the Arctic to the Antarctic, from the Carribean
to the Sea of Japan, Mediterranean and Black Seas. So far, the program has collected
over 150km of cores. These specimens are stored in four repositories around
the world, where they are available for scientific study. See a map of ODP drill
sites at
http://www-odp.tamu.edu/sitemap/sitemap.html. or , for Australian sites,
look in your Notebook.
Unlike commercial oil drilling ships the JOIDES Resolution cannot drill into areas where there might potentially be oil or gas. Ships that drill for oil and gas have a special attachment, called a riser, that connects the ship to the sea floor. The riser makes it possible to control the pressure in the hole by allowing the circulation of drilling mud. The drilling mud not only controls the pressure in the hole, it also carries the rock cutting to the surface.
Oil drilling ships are usually limited to drilling in water depths of less than 500m (although a ship, the Saipem 10,000, that can drill in depths of 3000 m has recently been built in Korea – before this semi submersible platforms were used to drill in water depths to a maximum of 1500m) However nothing comes close to the Resolution, which can drill in depths greater than 8km. In order to drill successfully the ship must hold a constant position directly above the borehole in the ocean floor. And it must be able to do this in waves, wind, and ocean currents. Because of the great depths, anchors are out of the question. This feat, known as dynamic positioning, is accomplished by 12 computer controlled thrusters. Ten of them are mounted on hydraulic pods that retract into the ship when it is underway. The ship uses satellite navigation systems to find the chosen drill site. When it is in position, transponders are dropped to the seafloor and the thrusters are extended beneath the ship. With the thrusters lowered, the bottom of the ship literally bristles with propellers. Computers on the ship use the transponder signals to activate the various thrusters, which can move the ship forward, backward or sideways. The result is that the Resolution literally "sails" in place. The Resolution can also drill relatively unperturbed in seas as high as 4m. Instead of being connected directly to the drill rig, the pipe string is suspended from a massive "heave compensator." This device functions like a huge shock absorber. If the ship rises on a wave, the heave compensator lowers the drill string. Technology developed by the ODP is used on the Saipem and will be used on any future deep water oil drilling ships.
The other notable difference between the Resolution and oil drilling
ships is the addition of 8 floors of laboratories. The "lab stack"
contains eleven laboratories including those for core handling, sampling, physical
properties, paleomagnetics, paleontology, chemistry, thin section preparation,
X-ray, photography, underway geophysics and microbiology. Much of the equipment
found on the JOIDES is state of the art and far more comprehensive than found
here at Sydney University.
You can inspect the laboratories and look at the sort of data collected by scientists
on the ship at the ODP site located at http://www-odp.tamu.edu.
The Ocean Drilling Program is scheduled to finish at the end
of 2003. The program is being replaced by IODP (Integrated Ocean Drilling Program).
This new program is multi-platform and will include deep riser drilling, Arctic
drilling and shallow water drilling (eg PROD - Portable Remotely Operated Drill,
developed at the University of Sydney). The new riser drill ship has been built
by the Japanese and is due to be launched early in 2002. It will initially be
used to drill into the seismegenic zone adjacent to Japan. There are plans to
use the ship to fulfil many a geologists dream of drilling down to the MOHO.
Visit Web sites: Scientific American has ‘Science at sea, a ship like no
other’ under ‘Explorations’, The Discovery Channel has ‘Where
did life begin’.
| www.oceandrilling.org |
| www.odp.usyd.edu www-odp.tamu.edu/ |
| www.sciam.com |
| www.discovery.com |
There are lots of different techniques now available for sampling
the sea floor.
Grab samplers and dredges are used to scoop-up sediments and rocks from the
surface. Different types of corers can be used to take samples of the top few
meters of sediment. Drilling rigs, like that found on the JOIDES Resolution,
can be used to take continuous core of sediment or rock from deep down in the
ocean floor.
Sometimes
scientists are just interested in the surficial sediments, in which case they
can use one of the many types of grab samplers available. Grab samplers usually
have some sort of bucket or jaws that close when the sampler hits the sea bed.
Here at the University of Sydney we often use a SHIPEK grab sampler.
< SHIPEK style grab sampler being retrieved
> On deck - sample in the stainless steal bucket
of the SHIPEK grab sampler
You might want to know what is on the sea bed surface if you are interested, for example, in sediment transport, distribution of contaminants or biological habitat. Chris Jenkins, here at the University of Sydney, has produced a data base of the sea floor properties around Australia. For example, Chris has used information collected from surficial sediments to create the map of bryozoan facies distribution (see below).
Bryozoa
are calcified colonial creatures, sand to gravel sized. They were responsible
for much of the Cenozoic geological buildup of the continental margin of southern
Australia. For more about the auSEABED database see either
computer > Topics > data analysis
or
http://www.es.usyd.edu.au/geology/centres/osi/auseabed/au7_web2.html
Grab samplers
are generally only good for collecting soft sediment, sand or perhaps gravel.
If you want rock samples you need something else. Dredge samplers are low tech
- essentially just a weighted cage that you drag along the sea floor. They are
used to collect basalt samples, bits of black smokers and sometimes coral.
Example of a rock dredge (from http://www.idromar.it/bottom.htm)
You can view a rock dredge being deployed on the Carolina Coast at http://www.ncsu.edu/coast/research/welcome.html.
Corers
are used to collect undisturbed samples of the top meters of the seabed. Gravity
or piston corers are generally used in areas of soft sediment. A gravity corer
is just a weighted pipe that is allowed to free fall into the water. Piston
corers are similar, but have a piston mechanism that is triggered when the corer
hits the bottom. The piston helps to prevent disturbance of the sediment.
> Piston corer being deployed in the Gulf of Papua. Notice the several hundred kg of lead weights attached to the top of the barrel. Another weight is attached to the rope that can be seen hanging down beside the barrel. This weight hits the seabed just before the barrel and triggers the piston. Cores of up to 6m were recovered on this cruise.
In
areas of sandy or gravelly sediment a vibro-corer can be more effective. There
are a number of different types of vibro-corers, from small portable ones to
large ones with submersible towers. What ever the size, they all use a combination
of weight and vibration to penetrate the sediment. However, even using a vibro-corer
it is difficult to get corers longer than about 3 meters in sandy or gravelly
sediment.
< Putting some extra weight on a small vibro-corer!
This corer uses a cement shaker attached to a clamp on the core barrel to produce
the vibrations. We managed to get cores of about 2 m long in these silty sand
banks of the Fly River Delta (PNG).
< Large vibro-corer being deployed in the Gulf
of Papua. The vibro-corer tower is about 6 m high. It is lowered to the sea
floor and supports the corer. The vibrating head can be seen attached to the
top of the core barrel.
> A portable vibro-core being deployed in Iron
Cove. The vibrating head is bolted onto the aluminium core barrel and lowered
over the side. Because the water is shallow here (only about 2 m) a frame or
tower is not necessary. In deeper water a frame of flotation buoys can be attached
to this corer to keep it upright on the sea bed.
In Iron Cove a polycarbonate core liner was used inside the aluminium barrel.
The water is drained from the top of the core then the barrel is cut to the
appropriate length and sealed with a cap. The advantage of the plastic liner
is that you can see the sediment, the barrels are easily cut and are light to
carry. In addition cores collected in plastic tubes can be x-rayed – a
process which reveals internal structures like graded bedding and laminations
In order to take long cores or collect samples from well below
the sea surface, drilling technology is required. Drilling into the sea floor
can be done from a number of different platforms – drill ships (like the
JOIDES Resolution), barges, semi-submersible drill rigs, jackup drill rigs,
PROD (portable remotely operated drill) and drilling platforms.
> PROD – the portable remotely operated
drill developed in partnership with the University of Sydney. PROD is a robotic
seafloor coring system that works in water to depths of 2000 metres and penetrates
100 metres into the seabed. It carries tools for both rotary coring of rock
and hydraulic piston coring of sediments.
The crew on the JOIDES Resolution lowering the core barrel with a new drill
bit attached, back into the hole. The ship sails with a crew of 65, which includes
rig floor personnel, the catering crew and merchant seamen. The rig floor personnel
work around the clock recovering rocks and sediments from the seafloor.
INSERT incorelab.jpg
Scientists on board the JOIDES Resolution examine the core.
The drill ship JOIDES Resolution obtained a core 480 km east of Florida –
which shows the dust and ash fallout from an asteroid impact that scientists
believe was responsible for mass extinctions including the demise of the dinosaurs.
The core was drilled 2,658 m below the ocean surface and 128 m below the ocean
floor.
The asteroid nearly 10 km wide slammed into what is now Mexico's Yucatan Peninsula. The impact blasted a 180 km wide crater in the Earth's surface, sending trillions of tons of debris into the atmosphere. A searing vapor cloud sped northward and, within minutes, set the North American continent aflame. Ash and soot darkened the skies for months and led to the global extinction of many plants and animals, including the dinosaurs. Other organisms, including mammals, somehow survived.
Dust and ash fallout as well as material blasted from the crater are clearly evident in the deep-sea core. By analyzing and dating the contents of each layer in the core, scientists have reconstructed what happened on that day 65 million years ago. Much of the story is told by foraminifera -single-celled organisms that have inhabited the oceans for more than 500 million years. The core contains sediments that range in age from 64.9 to 65.1 million years, which is the interval immediately before, during, and immediately after the asteroid impact.
At the base of the core a 10-centimeter slice is uniformly white
and chalky in appearance. This is the pre-impact, pre-extinction layer of sediments
containing microfossils from the time of the dinosaurs. Visible under a microscope
are large
ornate foraminifera from the Cretaceous Period that accumulated over tens of
thousands of years.
Above this layer an abrupt colour from chalky white to dark green occurs. This
15 cm section is the ejecta layer containing material blasted from the crater
and deposited in just days or months. Grading upward the sediment changes from
coarse and dark green to a thin band of finer orange-brown material that is
the fireball layer.
Fossils are replaced by tektites--glassy material that condensed and rained down from the hot vapour cloud produced by the impact.
The core quickly changes in hue from dark rust to lighter and lighter shades of grey, until the chalky white appearance returns. This area of the core, which extends about 12 cm, accounts for tens of thousand years. It is the post-extinction layer containing microfossils from the era after the dinosaurs. Only tiny, less ornate foraminifera survived, while a few new species evolved (Blast from the Past exhibition at the Smithsonian Institute).
Who? |
People and events which transformed marine studies to marine science |
Why? |
Salinity, global warming, El Nino, just to name a few |
Some of the terms, events, people and equipment associated with Marine Science.
In the three sections of this section, a myriad of instruments have been discussed. Obviously, the best way to become familiar with what can, can't and should be done with each one is best discovered by actual application. This, hopefully, is the next best thing - a hybrid of practical and theoretical application.
A bit of a no-brainer, but any exposure to 'nollige' is good exposure.
Additional information to allow you to test some of the ideas and concepts from this chapter.
- continental jigsaw?
- Challenger Path?
Sampling-type problems?
We realise that not everyone has had experience with the intrinsic concepts of Marine Science. This 'computer' has numerous examples which will help you understand these fundamental facets! Very helpful, very colourful!