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The Lo-o-o-ng Core

The deeper you can sample the seafloor, the further back in time you can go

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Since the early part of the 20th century, scientists have been going to sea on ships equipped with long, hollow pipes called corers. These corers are used to collect seafloor sediments, plunging into the ocean bottom and capturing long stratified plugs of the seabed. These sediments contain clues to a myriad of past conditions and events in the Earth’s oceans and climate.

Over decades, technology and methods for handling coring systems have become safer, and core samples have become longer, reaching 20 to 25 meters (60 to 80 feet) in length. This longer reach provides access to deeper, older sediments, and thus a look further back into Earth history.

In the 1970s, Charley Hollister at the Woods Hole Oceanographic Institution (WHOI) recovered an historic core from the Northeast Pacific. It contained one of the longest continuous records of ocean basin history: 65 million years—back to times when dinosaurs still roamed the planet. As scientists still do today, Hollister and colleagues studied tiny fossilized shells and fish teeth found in the core. Careful analysis of these remnants can reveal the temperature, water chemistry, and other characteristics of ancient oceans.

The ability to collect these long cores has neither been easy nor routine for U.S. oceanographers. However, in 2007, scientists will have an opportunity to explore Earth’s history with a newly developed coring system that will extract 45-meter (150-foot) cores from the seafloor—some of the world’s longest.

This massive instrument, weighing more than 30,000 pounds when assembled, is so large that the WHOI-operated 85-meter (279-foot) research vessel Knorr had to be specially modified to accommodate the handling of the system’s extreme length and weight (view slideshow). The new device is nearly twice as long and five times as heavy as existing coring systems in the U.S. oceanographic fleet.

Private donations to WHOI, including the Cecil H. and Ida M. Green Technology Innovations Awards Program and the Grayce B. Kerr Fund, provided funds for feasibility studies and conceptual design. The National Science Foundation provided major funding for the construction of the system. To date, more than $5 million has been invested in engineering, ship modification, and equipment construction.

Historically, coring systems have encountered problems recovering samples of the soft sediment on the ocean bottom because the large weight of the equipment stretched the long cables needed to lower it to the seafloor. The elongated cabled recoiled elastically, jerking the corer up after it penetrated the seabed and distorting the stratified layers that provide a chronology of past events in the ocean.
 
But an extremely strong, custom-made synthetic rope was designed for the WHOI long-coring system. Tests showed that even with a 35,000-pound load hanging in 15,000 feet of water, the rope would stretch less than 10 feet. This promises little recoil and high-quality cores with accurate records of past ocean conditions.

By the fall of 2007, the complex array of components of the coring system (view Flash) will be installed onboard Knorr, and sea trials will begin. The first cruise will be purely an engineering evaluation of all aspects of the system. Once in service though, the corer will be deployed all over the world oceans (view animation Quicktime or Media Player) to study climate history, sea-level change, and a variety of other scientific puzzles whose secrets are buried in sediments at the bottom of the sea.

Images

Article images (3)

Multimedia

videoSLIDESHOW

Refitting the Ship (4)

videoVIDEO

Launching and Recovering the Long Corer

Watch and hear how the long corer system works to recover sediments on the seafloor.

slideshowINTERACTIVE

The Sum of Unique Parts

A variety of one-of-a-kind components combines to maintain control of the 150-foot corer.

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