Eos, Vol. 79, No. 25, June 23, 1998 plication is that the smaller northward flow of the Outflow mixture allowed more of the warm North Atlantic Drift water to enter and warm the Nordic Seas in the early Holocene. This increase in westward diversion of Drift water from 8,000 B.P. to present might be larger than the likely additional increase in the diversion of Drift water westward in the next 70 years, but some storms even now move into the Baffin area, and the Baffin Is- land climate is quite close to the threshold of ice-sheet accumulation. Consequently, the inevitable increase of several percent in the Mediterranean Outflow in the coming cen- tury may decisively exceed the critical diver- sion threshold, trigger the dominant Reply PAGE 292 It is true that the model resolves only the large-scale circulation, but large-scale ther- mohaline overturning is responsible for over 80% of the heat transport in the North Atlan- tic. Johnson's basic premise that Mediterra- nean Outflow Water (MOW) upwells in high latitudes (near the Wyvilie-Thomson Ridge) to enter the Faroe-Shetland Channel and eventually the Norwegian Sea is neither sup- ported by a recent hydrographic data analy- sis that specifically looked at this question {McCartney and Mauritzen, 1998) nor by high- PAGE 291 W. L. Chameides and E. M. Perdue, Oxford University Press, New York, 224 pp., ISBN 0-19-509279-1, 1997, $49.95. Global biogeochemistry is the discipline that links various aspects of biology, geology, and chemistry to investigate the surface envi- ronment of the Earth. The global biogeo- chemical cycles of the elements lie at the very core of the subject and involve a myriad of processes that transform and transport vari- ous substances throughout the Earth's eco- sphere, which consists of the atmosphere, hydrosphere, shallow crust (soils, sedi- ments, and crustal rocks), biosphere, and cryosphere. As the authors of Biogeochemi- cal Cycles: A Computer-Interactive Study of Earth System Science and Global Change say, "anyone interested in understanding the causes of global environmental change and its implications for life would be well-advised storm-track switch over Labrador, cause ma- jor ice-sheet growth in Canada, and severely cool northern Europe. Unfortunately, pre- sent numerical models cannot adequately describe the details of the North Atlantic cir- culation that may cause this to occur.—R. G. Johnson, Department of Geology and Geo- physics, University of Minnesota, Minneapo- lis, USA References Adkins, J. R., E. A. Boyle, L. Keigwin, and E. Cortijo, Variability of the North Atlantic thermohaline circulation during the last inter- glacial period, Nature, 390, 154-156, 1997. Greatbatch, R. J., and J. Xu, On the trans- port of volume and heat through sections resolution circulation model results (A. Cow- ard, pers. commun., 1998; also see Web site http://www.soc.soton.ac.uk/JRD/OCCAM/ POSTERS/canigo_posterl .pdf). In recent research, M. S. McCartney and C. Mauritzen (pers. commun., 1998) show that there is no rise of water from the depths of the Rockall Trough into the Faroe-Shet- land Channel, and that the water entering the Norwegian Sea through that channel is de- rived from the North Atlantic Current. They find that the northward flow of the eastern boundary undercurrent of MOW fades in in- tensity through the Bay of Biscay and does not penetrate past Porcupine Bank into the Rockall Trough. Particle trajectories from the to begin with an investigation of global bio- geochemistry." This small but illuminating book is an attempt to provide a reasonably in- tegrated and comprehensive text dealing with the study of the life-essential global bio- geochemical cycles of carbon, phosphorus, nitrogen, sulfur, and oxygen. The book's best features are its overview of the biogeochemical cycles of the life-es- sential elements, its explanation of the princi- pal mechanisms and processes that determine their cycling behavior, their reser- voirs, and their fluxes, and its utilization of mathematical and numerical modeling as a means of transforming qualitative descrip- tions of the biogeochemical cycles into a quantitative analysis of the dynamics of the cycles. As a tool to aid in understanding the modeling, the authors have developed and included with the book a computer program which enables the reader to construct a nu- merical model of a biogeochemical cycle across the North Atlantic: Climatology and the pentads 1955-1959, 1970-1974, J. Geo- phys. Res., 98, 10125-10143, 1993. Kor, N., and E. Jansen, Response of the high- latitude Northern Hemisphere to orbital cli- mate forcing: Evidence from the Nordic Seas, Geology, 22, 523-526, 1994. Pollard, R. T., and S. Pu, Structure and circu- lation of the upper Atlantic Ocean north- east of the Azores, Prog. Oceanog., 14, 443-462, 1985. Reid, J. L., On the contribution of the Medi- terranean Sea outflow to the Norwegian- Greenland Sea, Deep Sea Res., 26, 1199-1223, 1979. Zahn, R., M. Sarnthein, and H. Erlenkeuser, Benthic isotope evidence for changes of the Mediterranean Outflow during the Late Quaternary, Paleoceanography, 2543-2559, 1987. OCCAM model (1/4 degree resolution in lati- tude and longitude) are consistent with this analysis. Only one of the more than 100 MOW particles tracked in the model moved north and upwelled into the Faroe-Shetland Chan- nel along the path advocated by Johnson. Johnson's claim that small changes in the Mediterranean outflow could trigger a new Ice Age is speculative at best. At a time when humanity is facing a real threat of climatic change and needs to decide on appropriate counter-measures, it is important that public scientific statements are sound and can be taken seriously.—Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Potsdam, Germany and its dynamics with minimal knowledge of differential equations and numerical tech- niques. As might be expected, there are several in- troductory chapters dealing with such topics as a rationale for studying the biogeochemi- cal cycles discussed in the book, some princi- ples of chemical thermodynamics, and a review of the Earth system, its hydrosphere, atmosphere, lithosphere, and biosphere. Un- fortunately, I find the thermodynamics and Earth system segments to be the weakest parts of the book. They are not developed ex- tensively enough to be of much use except to the totally uninformed reader for whom I do not think this book was written. As the authors say, this material can be skipped and the reader can move on to the heart of the text. However, one wonders, since the bio- geochemical cycles in this text are to a large extent governed by kinetic processes, why a chapter on kinetics would not have been as germane to the book as one on classical chemical thermodynamics. From Chapter 4 on, the text deals with global biogeochemical cycles—the heart of the book. In order to understand how a pertur- bation of a biogeochemical cycle will manifest itself in the cycle, it is necessary to develop a mathematical description of the cycle and the various processes that cause flow from one part of the cycle to another. The authors pro- BOOK REVIEW Biogeochemical Cycles: A Computer-Interactive Study of Earth System Science and Global Change This page may be freely copied.