Heard Island global warming test
By Robert C. Spindel
In late January and early February 1991, an international team will conduct an experiment to test the possibility of measuring global warming in the world’s oceans. The goal is to provide early indications of warming caused by the so-called greenhouse effect, the atmospheric buildup of CO, and other gases. The method is based on the principle that acoustic energy travels through water between a source and receiver at a speed determined primarily by the water temperature. Thus acoustic travel time can he used as a temperature gauge. The idea is an outgrowth of suggestions made by Professor Walter Munk of the Scripps Institution of Oceanography and Professor Carl Wunscb of MIT in the early 1980s to use long-range underwater acoustic transmissions to measure changes in the heat content of the oceans. The possible effects on global temperatures and sea levels of a projected twofold increase in CO, and other greenhouse gases by the middle of the next century have been widely discussed in the scientific and popular literatures; they are a major aspect of (possibly dramatic) global climate change. Unforn210 Environ. Sci. Technol.. Vol. 25. NO. 2. 1991
Robert Spindel
nately, the projections are uncertain because they are based on numerical models of atmospheric and oceanic responses to the greenhouse effect that lack consistent and reliable input data. Of particular concern is the dearth of warming rate data. Direct atmospheric measurement of surface warming, estimated to be about 20 millidegrees Celsius per year, is difficult because of contamination (from urban “heat islands,” for example), and wide fluctuations in the ambient background. In addition, greenhouse warm-
ing and inherent variability have similar spatial patterns. By contrast, the expected greenhouse signal in the ocean, estimated to be 3-5 millidegrees Celsius per year at loo0 m depth, is substantially different from the pattern of natural oceanic variability, and furthermore the background temperature fluctuations in the ocean are much smaller than those in the atmosphere. All this suggests that the ocean is a robust environment for detecting small, underlying trends. An increase in water temperature of 1 “C produces a 4 - d s change in the nominal 1500-m/s ocean sound speed. Global ocean warming of 3-5 millidegrees Celsius per year will produce a sound speed increase of up to 0.02 ds.Over global paths (16,000 mi) this results in a travel time reduction of 0.1-0.2 s per year, an easily measured change. This decrease must be detected against travel time fluctuations caused by oceanic variability arising from sources other than greenhouse warming. Such travel time “noise” is largely due to mesoscale, seasonal, and longer tern variability. Estimates are that it will take approximately 10 years of observation to establish an underlying trend associated with greenhouse warming. Thus, the January-February test is exploratory,
0013-936X191/0925-210$02.50/0 @ 1991 American Chemical Society
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Sound path
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the forerunner of a possible decade-long experiment. In the test, acoustic signals will be transmitted for I O days from a location near Heard Island in the southern Indian Ocean to receiver sites scattered around the globe. A variety of signal types at frequencies between 50 and 70 Hz will be transmitted in order to determine optimal wave forms and minimum required signal energy. The Heard Island site is unique (Figure I ) because from there sound can travel through parts of all the major Oceans without being obstructed by land masses or seamounts. The transmissions will be monitored in Australia, New Zealand, and the Fiji Islands in the Pacific; Antarctica, the United States, South America, Ascension Island, and Bermuda in the Atlantic; and South Africa, India, Christmas Island, and the Kerguelen Islands in the Indian Ocean, to determine whether received signal-to-noise levels are sufficiently high to measure travel times with the required precision (Figure 2). An experiment conducted in 1960, in which the echoes of 300-pound explosive underwater charges detonated near Perth, Australia, were received at Bermuda (some 20,000 mi distant and 13,350 s later) provided dramatic evidence of long underwater acoustic paths. Such long paths are possible because of a natural oceanic waveguide that con-
i s around the w
FIGURE 2
Computer siw*’-+b,n oftrayel *im- changes along three path fromHeard Is1 o Btwmudr is Bay (Oregon), and San Francim I
Bermudan
1J Coos Bay. Oregon
San Francisco
fines acoustic energy to a duct, so that it propagates without incurring losses due to bouncing or scattering from the surface or bottom. The so-called deep sound channel arises as a result of refraction in the vertical plane; sound speed is high near the surface where water is warm, decreases with depth as a
result of cooling, and increases again as the growing effect of pressure increases density. At Heard Island the axis of the sound channel, that is, the depth of minimum sound speed, is at -200 m. It deepens to -1500 m near the equator and shoals to -1300 m at the latitude of Bermuda. The acoustic source will be Environ. Sci. Technol., Vol. 25, No. 2,1991
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lowered from a ship to 200 m. Receivers will be placed at depths corresponding to the local sound channel axis depth. The scientific team is led by Walter Munk of Scripps, Andrew Forbes of Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, Theodore Birdsall of the University of Michigan, Arthur Baggeroer of MIT, and myself. Funding for the experiment has been provided in the United States by the National Science Foundation, the Office of Naval Research, the Department of Energy, and the National Oceanic and Atmospheric Administration. In Australia funds have been provided by CSIRO (Heard Island is an Australian territory). Listening sites will be staffed by scientists from MIT, the University of Michigan, NOAA, Scientific Applications Inc., and the Monterey Bay Research Institution. International participants include scientists from Brazil, Canada, France, India, Japan, New Zealand, South Africa, and the Soviet Union.
Spectroscopic Characterhationof ere is an overview of the powerful spectroscopic methods in use today for characterizing crystal structure, chemistry, morphology, and excited states of minerals. With a triple focus, this new summary of the latest techniques emphasizes:
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Additional reading Bryan, K.; Manabe, S.; Spelman, M. J. Journal of Physical Oceanography 1988,18, 851-67. Munk, W. H.; Forbes, A.M.G. Journal of Physical Oceanography 1989, 19, 1765-78. Munk, W. H.; Wunsch, C. Philos. Trans. R . Soc. London 1982, A307, 439-64. Serntner, A. J.; Chemin, R. M. J . Geophys. Res. 1988, 93, 505-22.
Robert C. Spindel is director of the Applied Physics Laboratory, professor of electrical engineering, and adjunct professor of oceanography at the University of Washington. The laboratory conducts basic and applied research programs in ocean and polar science, ocean technology, ocean acoustics, and experimental physical oceanography. He received his B.S. degree in electrical engineering fiom Cooper Union, and an M.S. degree and Ph.D. in electrical engineering from Yale University. He has written or coauthored more than 80 scientific and technical papers, holds several patents, and has served as chief scientist on many research cruises. He is presently developing instrumentation and techniques to apply tomographic methods to large-scale ocean measurements.
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the structural and physical properties of minerals that have been associated with promotion of chemical reactions on their surfaces the fact that most naturally occurring minerals store electronic energy in quantlties sufflcient to significantly alter some of their properties, and the spectroscopic means by which biologically deposited minerals can be distinguished from geologically deposited ones
Twenty-three chapters describe a variety of iew applications of mineral spectroscopy to jetermine composition, purity, interaction Nith energy, characterization of active centers, and adsorbate interactions. A discussion of ionoptical methods includes instruction on low to describe a mineral and its surface before studying it. Other chapters focus on en?rgy storage within minerals. A section on acLive centers uses clays as a model, because in spite of its complexity, it is one of the most mportant classes of natural reactive minerals. If you are a physicist, chemist, geologist, or %el,soil, agricultural, and environmental sci?ntist interested in interfacial chemistry of ~eologicalsurfaces, this book will stimulate {our thinking and inspire you to try these new :haracterization methods. telia M. Coyne, Editor, San Jose State University Stephen W.S. McKeever, Editor, Oklahoma State University David F. Blake, €ditor, NASA-Ames Research Center
Developing a Chemical Hygiene Plan
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his essential “how-to” book tells you what you need to know to comply with the federal regulation known as the “OSHA Laboratory Standard” which requires chemical hygiene plans. Developed by the ACS Committee on Chemical Safety, the guide presents hygiene plans that can be modified according to the particulars of individual laboratories. Among the topics covered in this valuable book you’ll find 0 0
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In addition, several appendices are provided, including employee information and training techniques, exposure assessment procedures, the elements of an emergency procedure plan, the OSHA Laboratory Standard, a list of contacts for states that have OSHA-approved state plans, and a list of acronyms. This reference is critical to all lab supervisors who must have in place by January 31, 1991, a chemical hygiene plan that outlines specific work practices and procedures ensufing employee protection from health hazards associated with hazardous chemicals. by Jay A. Young, Warren K, Kingsley, and George H. Wahl
Developed from a symposium sponsored by the Division of Geochemistry of the American Chemical Society
Developed by the Committee on Chemical Safety of the American Chemical Society
ACS Symposium Serles No. 415 492 pages (1 989) Clothbound ISBN 0-8412-1716-5 LC 89-27755 $94.95
72 pages (1990) Paperbound ISBN 0-8412-1876-5 LC 90-46721
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