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2. Scientific Motivation for Ice Coring Ice is a major component of the global climate system. The cycles of glaciations and interglacials are among the most spectacular and intriguing climatic changes in the history of the Earth. Aside from the age-old scientific quest to understand the causes of ice ages and to predict the next glaciation, the current ice areas are an important part of today's climate. How they were formed, whether they are shrinking or growing, and how they will interact with the coming century's climatic forcings are key questions being asked by those active in the attempt to formulate a quantitative theory of climate. An understanding of present and future climate will come about only with accurate documentation of the natural experiments of the past. The physical, mechanical and geochemical properties of ice cores provide one of the most detailed and quantitative sources of information for the reconstruction of climate history (Dansgaard and others, 1971, 1984; Oeschger and others, 1984; Lorius and others, 1985). Numerous national and international groups have issued statements on the importance of these issues, including many private businesses or foundations (Electric Power Research Institute) agencies of the U.S. government (DOE/EV/10098-5; EPA 230-09-007), and other national governments and international bodies including the United Nations, the International Council of Scientific Unions, International Climate Research Program (ICRP), the World Meteorological Organization, all of which indicate the societal need to understand the ice-covered parts of the Earth.

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10 As snow accumulates on the surface of an ice sheet it preserves information related to atmospheric temperature, which is revealed by measuring oxygen and hydrogen isotopic ratios (Dansgaard and others, 1971). The snowfall also incorporates within its layers solid dust and pollen particles (Thompson and Mosley-Thompson, 1981; Petit and others, 1981), ionic components (Davidson and others, 1981; De Angelis and others, 1984; Herron and Langway, 1985), and trace metals (Wolff and Peel, 1985). The concentrations of these components are related to the wind pattern and conditions on the land and ocean surfaces. For example, these impurities record debris peaks resulting from significant volcanic eruptions (Hammer, 1980V Radioactive isotopes produced by cosmic rays (e.g. 14C, 10Be, 26A1, and 36C1) also become embedded in snow deposits at concentrations that depend on solar activity and geomagnetic variability (Stuiver and Quay, 1980; Oeschger, 1982; Elmore and others, 1982 and 1984). Atmospheric gases are entrapped naturally in glacier ice as air bubbles, providing the only known source of prehistoric samples of atmospheric gases (Stauffer and others, 1985; Rasmussen and Khalil, 1984, Craig and Chou, 1982). The variations in concentration of greenhouse gases such as CC^, methane, and others are of special importance in developing theories of climatic change. All of these many components are deposited and preserved in annual layers and provide a detailed record book of the past. At many locations, some properties vary on an annual cycle, the variation of which identify the annual ice layers (Hammer and others, 1978, 1985; Thompson and others, 1979; Herron 1982a, b). This imprint may last for thousands of years in some locations. It enables the glacial archives to be read with fantastic detail and provides a means for dating akin to tree rings. On longer time scales the information contained in annual layers is smoothed out, but resolution on the order of decade or century time scales may still persist at ages of more than 100,000 years. The high time resolution has revealed startling indications of dramatic climatic changes occurring abruptly in the course of a few decades (Stauffer and others, 1985). This possibility has important implications for human activity. Current theories of climatic change place great importance on the role of anthropogenic pollutants in the atmosphere. Most important are trace greenhouse gases

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11 such as CO2 and methane. It is also important to monitor pollutants such as sulfates and toxic heavy metals (Boutron and Paterson, 1983; Wolff and Peel, 1985). The dispersal of these pollutants through the atmosphere can be studied in the ice sheets and ice caps. Even the very recent ice layers are of interest, because they catalogue the deposition of pollutants in remote places where there are no observing stations. Similarly the ice provides old samples needed to establish natural background levels and variations existing before intervention by major human activity. Carbon dioxide is now considered to be an especially important anthropogenic pollutant that could affect climate. The well-known rise in CO2 concentration caused by industrialization in the last few centuries is recorded in the ice (Delmas and others, 1980; Neftel and others, 1982, 1985; Raynaud and Barnola, 1985). An important discovery is that a major natural increase in COj concentration occurred at or possibly preceding the endof the last glaciation (Stauffer and others, 1985). This observation is important in the quest to predict the climate impact of anthropogenic CC^. Knowledge of the relationship between CC^, sea level, climatic conditions, glacier sizes, and other environmental variables is essential to any comprehensive, credible theory of climate. Methane also has a greenhouse effect. It is produced by biological processes (Rasmussen and Khalil, 1981; Khalil and Rasmussen, 1983a). Analysis of the gas extracted from ice cores has shown that methane concentration started to increase markedly about 200 years ago (Rasmussen and Khalil, 1984). The cause may be related to agricultural practices and population growth. Were there significant natural variations in the past? What were they? These are questions ice coring can answer. Research frontiers exist in the measurement of many other climatically important gases such as the oxides of nitrogen (Khalil and Rasmussen, 1983b) and chlorofluorocarbons. Extremely old ice lies deep within the Greenland and Antarctic ice sheets. Analyses of core from Vostok, East Antarctica, are currently under way by the French (Lorius and others, 1985). The ice only midway through the total ice thickness is about 150,000 years old. Much older ice can be reached in both polar ice sheets to extend the glacial time series of climatic indicators back over more than one glacial cycle, thus opening the opportunity to

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12 make detailed interhemispheric comparisons complementary to those from ocean cores. Climatic changes occur in a globally coupled system that involves feedbacks on various geographical and time scales. An understanding of climate processes requires a broad geographical picture that can be reconstructed for the past only by means of a wide spectrum of paleoclimatic indicators in the terrestrial, marine, and ice environments. The unique spectrum of geochemical indicators found in ice can be exploited in high-altitude ice caps at lower latitude locations. The ice at these locations is probably limited to a few thousand years old (Swithinbank, 1974; Thompson and others, 1984a), but holds opportunity for contributing to a geographically broad definition of climate fluctuations operating over the shorter time scales, which are of most immediate concern to human activity. Analyses of ice cores from the Quelccaya Ice Cap in Peru have shown that El Nnfo-Southern Oscillation events are recorded in the ice and a multicentury history of occurrence can be reconstructed (Thompson and others, 1984b, 1985). Ice cores are needed by glaciologists to understand the dynamics of ice flow based on the physical properties of the ice column and the interface with the bed beneath. Concerns about the stability of ice sheets and the rapidity with which they might change have recently been brought to the forefront in relation to the potential response to CC^-induced climatic warming and sea level change (National Research Council, 1985b). Knowledge of the ice flow also contributes to the dating of ice obtained at different levels in a drill hole (Dansgaard and Johnson, 1969) and to interpretation of layer thicknesses in terms of past accumulation rates (Paterson and Waddington, 1985). A parallel effort to model the dynamic history of ice caps and ice sheets is needed to provide a clear reading of the ice core record book. It is important to note that ice coring activities need to interface with many other disciplines in order to provide the most cost-effective use of research resources across the earth sciences. This is essential to achieve the comprehensive geographic and time coverage that is needed, but also to strengthen interpretation through use of a variety of indicators. For example, in order to prove the tentative identification of a rapid climatic change event in the past (Stauffer and others, 1985), it is important to have evidence for such an event in more

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13 than one location or proxy method. A local match of ice core stratigraphy or chemical records with that of a nearby set of offshore deep sea cores could prove invaluable to the interpretation of both sets of proxy records. Lake sediments, deep-sea sediment cores, prehistoric beaches, and glacier moraines are all examples of other sources of proxy information, which are currently used to study the earth's climatic history. All major efforts to advance the knowledge and predictive capacity of climate-related disciplines have stressed the importance of understanding the active role of ice and of unraveling the extraordinary history of past environments contained in them. Ice coring is the principal means to advance our collective knowledge in these areas. A new carefully preplanned, comprehensive, and integrated ice core drilling and analysis program is essential. The recent successfully completed Greenland Ice Sheet Program (GISP) at Dye 3, Greenland, is a prime example of what can be accomplished when the full force of modern day glaciological technology is unified into a field and laboratory team effort, as was done by the State University of New York (SUNY), Buffalo, the University of Copenhagen, and the University of Bern (Langway and others, 1985b).