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'New window' on earth's climatic record.

'New window' on earth's climatic record

Nuclear magnetic resonance imaging, the technology that allows physicians to look at cancer cells and brain lesions, has for the first time been used to examine core samples taken from the ocean floor. The images produced so far show new details in the sedimentary record -- details that may help scientists assemble a 200,000-year record of changes in the earth's climate, according to Madeleine Briskin, who pioneered the application of the technique.

"This is opening a whole new window for us," says Briskin, a geologist at the University of Cincinnati, who used the technique on sediments from the Gulf of California. Her report is to appear in the August GEOPHYSICAL RESEARCH LETTERS.

The primary advantage of nuclear magnetic resonance imaging, or MRI (until recently called NMR), is that it reveals differences between layers that are rich in organic material and those that contain few organic remains, Briskin says. The richly organic layers show up as light bands, and the layers lacking in organic material appear dark. X-rays, the usual technique for studying core samples, do not make this differentiation.

The ability to distinguish the two kinds of layers makes it possible, for the first time, to tell where one year's worth of sediment ends and the next begins, because each year's deposit contains one richly organic layer (laid down in summer) and one layer with relatively little organic material (deposited in winter), Briskin explains.

Each annual layer, known as a varve, contains organic evidence of the earth's climate and ocean temperatures for the year it was deposited, Briskin says. A long sequence of varves, in turn, records cycles in the earth's climate. "It is a measure of what has gone on at the surface of the planet," Briskin says.

Scientists customarily look at tree rings for evidence of climatic cycles, but the record in ocean sediments stretches back much farther -- to about 200,000 years ago, Briskin says.

This sedimentary record, in turn, can be correlated with cycles that are believed to influence climate -- such as sunspot activity, changes in the earth's orbit, El Ninos and cycles of the moon. Briskin told SCIENCE NEWS. "The implications for this are remarkable," she says.

George Kukla of the Lamont-Doherty Geological Observatory in Palisades, N.Y., says he intends to follow Briskin's example by using MRI on lake sediments. "It's a really great new prospective method," Kukla says. "We are pretty excited by [Briskin's] results."

To make her images, Briskin borrowed MRI equipment used by physicians at the Magnetic Resonance Center of San Diego. It uses both radio waves and magnetic fields to make images. The radio waves excite the hydrogen atoms in the substance to be imaged. When the beam is turned off, the magngetic fields pull the atoms into alignment. The equipment reads the various movement rates of the hydrogen atoms of different materials and, with that information, creates an image of the internal structure.

Because the equipment uses a number of nonuniform magnetic fields superimposed over a background static field, it is able to create a very detailed image. By making a series of such images, MRI also makes it possible to put together a three-dimensional picture of the core sample, Briskin says, which would give researchers more information about the annual constituents of a particular sediments sample. An additional advantage is that researchers can make the images without cutting into the core sample.

X-rays, which are fuzzier, come in only two dimensions and require that the core sample be cut into pieces, Briskin says.

But Briskin does not suggest that MRI should replace X-rays altogether. X-rays can delineate some very fine layers that do not show up as well with MRI. These layers may represent seasonal deposits within varves. By relating the seasonal layers on X-rays to the varves on MRI images, scientists can get a very detailed picture, Briskin says.

One major drawback of MRI is its expense, however. One set of MRI equipment runs about $2 million. Briskin spent $960 an hour, for a total of about 15 hours, to use the equipment in San Diego.
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Title Annotation:magnetic resonance imaging used to examine core samples from ocean floor
Author:Murray, Mary
Publication:Science News
Date:Jul 26, 1986
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