Marine Ecosystems and Climate Variations. The North Atlantic – A Comparative Perspective
Nils C. Stenseth, Geir Ottersen, James W. Hurrell & Andrea Belgrano (Eds)
Oxford: Oxford University Press, 2004
266 pp., ISBN 0 19 850748 8
From the beginning of the 1990s, an extensive number of articles on the North Atlantic Oscillation (NAO) and its impacts has been published, and the annual number of articles is still increasing. In 2003, the first monograph book on the issue appeared. The American Geophysical Union issued “The North Atlantic Oscillation. Climate Significance and Environmental Impact” (AGU Geophysical Monograph 134). The book focused on the physics behind the NAO, its causes, and predictability. The book concluded with three chapters on the impacts on marine, terrestrial and freshwater environments. The present book “Marine Ecosystems and Climate Variations” follows up the impact issue with a broad emphasis on marine climate variation effects, in general, and the impacts of the NAO in the North Atlantic, in particular. Forty authors have written 16 chapters divided into six main parts. With such a large number of contributors it is a challenge to keep the content, ranging from phytoplankton to top predators, uniform and focused. However, with the focal point on the impacts of this single climate phenomenon, the NAO, the editors (and the authors) have elegantly managed to present the content in a coherent way. In addition, each of the main parts starts with an introduction to the succeeding chapters and this contributes to highlighting the connections between the topics. Hence, the book as a whole is nicely readable for a wide spectrum of natural scientists beyond ecosystem specialists. An extensive list of references makes it possible for the interested reader to investigate deeper the various topics. The book is a very good contribution to the overall objectives of the IGBP programme Global Ocean Ecosystem Dynamics (GLOBEC).
Part I, “Background to climate variation and its effects on marine ecology”, consists of three chapters. The first chapter is a general introduction to the ecological effects caused by climate fluctuations and gives an interesting discussion about direct and indirect climate effects and linear and non-linear effects on the ecosystem. The second chapter gives a detailed overview of the physics of the NAO, with emphasis on the elements of particular relevance to marine and fisheries biologists. The third and last chapter of Part I describes the development of physical–biological modelling, a science not much older than 20 years. The authors emphasize the multidimensionality of ecosystem dynamics, which needs to be addressed by quantitative modelling. Part II, “Plankton populations”, consists of two chapters, one on phytoplankton and one on zooplankton. Interestingly, the NAO seems to influence variations in zooplankton populations in a more pronounced way than in phytoplankton production. Part III, “Fish and seabird populations”, also consists of two chapters, one on each of the two trophic levels. The chapter on fish reviews the extensive literature on fish and climate, which particularly comprises how cod and herring in the North Atlantic respond to a wide range of physical processes, including the NAO. The chapter on birds emphasizes the lagged responses of bird populations to climate signals due to indirect propagation through trophic transfer and due to high longevity. In this way, the NAO signal seems to be less clear than on the lower trophic levels. Part IV, “Community ecology”, consists of three chapters on phytoplankton, benthos and fish. The chapter on benthos also clearly shows a response to NAO-associated forcing. The other two chapters, on phytoplankton and fish, could have easily been amalgamated into the previous chapters on these issues. Part V, “Climate impacts on North Atlantic marine ecology – views from outside”, is perhaps the most interesting part of the book for North Atlantic marine scientists. Here we obtain important perspectives from colleagues working in other systems, i.e. the Central Pacific, the Northeast Pacific, freshwater ecology systems, the influence of freshwater run-off to the ocean, time lags in terrestrial and marine environments, and a comparison between ENSO and NAO impacts. Part VI, “Conclusions”, and the afterword summarize and synthesize the book in a very good way.
No doubt the focus on the impacts of the NAO on the marine environment during the last 10 years has brought us a step closer in understanding the effects of climate variability on trophodynamics. However, the NAO is an extremely large-scale and integrated climate signal that comprises many variables and processes and, hence, often masks the causal links. This is also taken up in a statement from the concluding chapter: “A weakness of many climate–ecology studies is that although the observed patterns may be clear, the understanding of underlying mechanisms is often weak. There is therefore a pronounced need for proper experiments exploring the underlying causal mechanisms.”