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What Fish Can Hear About Changing Climate
| Article
# : |
10945 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
5 / 1993 |
2,762 Words |
| Author
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William P. Paterson
William P. Patterson is currently a doctoral fellow in
geochemistry at the University of Michigan at Ann Arbor. |
Not long ago the word climate referred to the stable temperature patterns that, though they changed from season to season, were predictable from year to year. That may be changing. The word climate is today often accompanied by the word change. Scientists are trying to determine whether man is changing his climate and, if so, to what degree.
History, as always, is a valuable teacher. Knowing how climatic changes in the past influenced life on earth would help us determine whether we have cause for concern because of the climatic changes that are taking place today.
Various ingenious strategies are used to study past climate, and recently a team at the University of Michigan devised a technique no less clever. They discovered that the chemical composition of the otoliths, the innerear bones of fish, changes with the temperature of the water in which they live. By studying this phenomenon in fish fossils yet another clue to past climate can be had that in turn can help us better understand our own changing climate. Techniques for analyzing ancient climate
The following is a summary of the techniques that are commonly used to estimate the climate of the past.
Ice cores. In areas of the world with net snow accumulation, a detailed climatic record can be obtained by examining ice cores. Every year a thin layer of snow is added to an ice sheet. Dust accumulating between seasonal snowfalls appears as a dark band from which scientists can determine the number of years represented by the ice core, which may represent a period of time in excess of 100,000 years. Cores are generally taken from higher elevations upon the ice surface, where little snowmelt or sublimation occurs. Because the isotopic composition of ice (as described below) varies with temperature, the information that can be obtained includes precipitation amounts, air temperature, atmospheric composition, and volcanic activity (ash). Ice cores do have their weakness in that they represent relative changes in climate (i.e., trends), and they are also subject to stress and strain that may disrupt the record so that cores taken as close as 30 meters apart may show different records.
Ocean sediment cores. Marine sediments provide many ways to evaluate paleoclimate. Isotopic analyses of well-preserved marine organisms reveal the long-ago changes that took place in ocean composition and temperature. Unfortunately, physical missing of sediment (and therefore the organisms) by
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